RFC 2625
IP and ARP over Fibre Channel
RFC 2625: IP and ARP over Fibre Channel ✨
okay bestie, let's talk about this one 🦋 It's RFC 2625, written by M. Rajagopal, R. Bhagwat, and W. Rickard from Gadzoox Networks. It's a Standards Track doc, dated June 1999. The header doesn't list anything it obsoletes or updates, so it's standing on its own 💅 Network Working Group is the group behind it.
Status of This Memo
okay so this part says the doc is an Internet standards track protocol for the Internet community 🌸 It's asking for discussion and suggestions for improvements. If you want to know where it stands, check the current edition of "Internet Official Protocol Standards" (STD 1). Distribution is unlimited, so share it with everyone 💜
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved. Standard legal stuff, but it's there 🎀
Abstract
Fibre Channel (FC) is a high speed serial interface technology 🔥 It supports a few higher layer protocols, including Small Computer System Interface (SCSI) and Internet Protocol (IP). Until now, SCSI has been the only widely used protocol over FC 🫶 The existing FC standards [3] don't properly spell out how IP packets get carried over FC, or how IP addresses get resolved to FC addresses 😭 So this doc specifies how to encapsulate IP and Address Resolution Protocol (ARP) over Fibre Channel, and it describes a mechanism (or mechanisms) for IP address resolution. Main character energy ✨
Table of Contents
1. Introduction ............................................... 3
2. Problem Statement .......................................... 5
3. IP and ARP Encapsulation ................................... 5
3.1 FC Frame Format ........................................ 5
3.2 MTU .................................................... 7
3.2.1 IP MTU ........................................... 7
3.2.2 Maximally Minimum IPv4 packet .................... 8
3.2.3 ARP MTU .......................................... 8
3.2.4 FC Data Field containing FARP Packet ............. 9
3.3 FC Port and Node Network Addresses ..................... 9
3.4 FC Sequence Payload Format ............................. 10
3.5 Bit and Byte Ordering .................................. 12
4. ARP ........................................................ 12
4.1 Address Resolution .................................... 12
4.2 ARP Packet Format ...................................... 13
4.3 ARP Layer Mapping and Operation ........................ 15
4.4 ARP Broadcast in a Point-to-Point Topology ............. 16
4.5 ARP Broadcast in a Private Loop Topology ............... 16
4.6 ARP Broadcast in a Public Loop Topology ................ 16
4.7 ARP Operation in a Fabric Topology ..................... 17
5. FARP ....................................................... 18
5.1 Scope .................................................. 18
5.2 FARP Overview .......................................... 18
5.3 FARP Command Format .................................... 20
5.4 Match Address Code Points .............................. 22
5.5 Responder Flags ........................................ 23
5.6 FARP Support Requirements .............................. 24
6. Exchange Management ........................................ 25
6.1 Exchange Origination ................................... 25
6.2 Exchange Termination ................................... 25
7. Summary of Supported Features .............................. 25
7.1 FC-4 Header ............................................ 25
7.2 R_CTL .................................................. 26
7.3 F_CTL .................................................. 27
7.4 Sequences .............................................. 28
7.5 Exchanges .............................................. 29
7.6 ARP and InARP ......................................... 30
7.7 Extended Link Services (ELS) ........................... 31
7.8 Login Parameters ....................................... 31
7.8.1 Common Service Parameters - FLOGI ............... 32
7.8.2 Common Services Parameters - PLOGI ............... 32
7.8.3 Class Service Parameters - PLOGI ................. 32
8. Security Considerations .................................... 32
8.1 IP and ARP Related ..................................... 32
8.2 FC Related ............................................. 32
9. Acknowledgements ........................................... 33
10. References ................................................ 33
11. Authors' Addresses ........................................ 35
Appendix A: Additional Matching Mechanisms in FARP ............ 36
Appendix B: InARP ............................................. 40
B.1 General Discussion ..................................... 40
B.2 InARP Protocol Operation ............................... 40
B.3 InARP Packet Format .................................... 40
B.4 InARP Support Requirements ............................. 41
Appendix C: Some Informal Mechanisms for FC Layer Mappings .... 42
C.1 Login on cached Mapping Information .................... 42
C.2 Login on ARP parsing ................................... 42
C.3 Login to Everyone ...................................... 43
C.4 Static Table ........................................... 43
Appendix D: FC Layer Address Validation........................ 44
D.1 General Discussion ..................................... 44
D.2 FC Layer Address Validation in a Point-to-Point Topology 45
D.3 FC Layer Address Validation in a Private Loop Topology . 45
D.4 FC Layer Address Validation in a Public Loop Topology .. 45
D.5 FC layer Address Validation in a Fabric Topology ....... 46
Appendix E: Fibre channel Overview ............................ 47
E.1 Brief Tutorial ......................................... 47
E.2 Exchange, Information Unit, Sequence, and Frame ........ 48
E.3 Fibre Channel Header Fields ............................ 49
E.4 Code Points for FC Frame ............................... 52
E.4.1 Code Points with IP and ARP Packet .............. 52
E.4.2 Code Points with FARP Command ................... 54
Appendix F: Fibre Channel Protocol Considerations.............. 58
F.1 Reliability in Class 3 ................................. 58
F.2 Continuously Increasing SEQ_CNT ........................ 58
Appendix G: Acronyms and Glossary of FC Terms ................. 60
Full Copyright Statement ...................................... 631. Introduction 🧚
Need
okay so Fibre Channel is a gigabit speed networking tech, and it's mostly used for Storage Area Networking (SAN) 🔥 It's standardized under the American National Standard for Information Systems of the National Committee for Information Technology Standards (NCITS), and it has a bunch of documents covering its protocols, operations, and services.
Right now FC is mostly used for storage devices and servers talking via SCSI 💀 Most servers still talk to each other over LANs. There is an FC Standard [3] that architecturally supports IP encapsulation and address resolution, but it isn't specified well enough 😭 [3] prohibits broadcasts, so loops aren't covered, and [10] has no support for Class 3.
So people have been doing their own nonstandard thing with IP over FC. Once there's a fully specified standard method, servers can talk to each other directly over IP on FC, which could boost performance for server host-to-host communication 🚀 This is going to be especially useful for Clustering Applications, iykyk 🫶
Objective and Scope
The main goal here is to promote interoperable implementations of IPv4 over FC ✨ This spec describes how to encapsulate IPv4 and Address Resolution Protocol (ARP) packets over FC. It works with any FC topology (loop, fabric, or point-to-point) and any FC class of service (1, 2, or 3) 👑 It also describes a FC Address Resolution Protocol (FARP) for associating World Wide Port Names (MAC addresses) and FC Port identifiers.
There's also a secondary goal: describing other optional address resolution mechanisms 💖
- Other FARP mechanisms that directly build IPv4 address and FC Port Identifier (Port_ID) associations.
- Inverse ARP (InARP) that allows learning the IP address of a remote node given its World Wide Port Name (WW_PN) and Port_ID.
Multicasting in Fibre Channel is defined as an optional service [11] for FC Classes 3 and 6 only, with no definition for Classes 1 and 2 🙈 Right now there are no vendor implementations of this service for either class. Broadcast service in FC can be used to do multicasting, just less efficiently. As far as anyone can tell, there aren't any IP applications over FC that need IP multicasting, so this spec does not support IP Multicasting 🦋
Organization
the vibe of the rest of the doc, bestie: Section 2 states the problem this spec solves 💅 Section 3 covers how IP and ARP packets get encapsulated in an FC sequence. Section 4 is about the ARP protocol (IP address to WW_PN). Section 5 covers the FARP protocol used for FC Layer mappings (WW_PN to Port_ID) 🌈 Section 6 is about "Exchange" Management in FC. Section 7 is the summary section, your quick reference for FC header settings, FC Link Service Commands, supported features in ARP, FARP, InARP, FC Sequences, FC Exchanges, and FC Login Parameters ✨ Section 8 discusses security 🔥 Section 9 thanks the technical contributors, and Section 10 lists the references. Section 11 has the authors' addresses 🎀
The appendices are just as iconic 🧚 Appendix A covers other optional FARP mechanisms. Appendix B covers Inverse ARP (WW_PN to IP address) as an alternate, optional way to build MAC and IP address associations. Appendix C lists some informal mechanisms for FC Layer Mappings. Appendix D talks about validating FC-layer mappings across the different FC topologies. Appendix E is a brief overview of FC Protocols and Networks. Appendix F covers reliability in Class 3 and Sequence Count FC Protocol issues. Appendix G has the acronyms and a glossary of the FC Terms used in this spec 💜
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [19]. Those words are doing real work in this spec, so read them carefully, periodt 💅
part 1 of 13 done, bestie 💖 more parts coming, so stay tuned 🌸
2. Problem Statement 🎀
okay so this spec is here to tackle two problems 💅:
- a format definition and encapsulation mechanism for IPv4 and ARP packets over FC
- mechanisms for Address Resolution
like I said earlier, the existing FC Standard [3] ([10]) is NOT enough to solve these 😭. the Fibre Channel Association (FCA)[1] came up with a solution to both problems first. quick tea: FCA is an industry consortium of FC vendor companies, not a Standards Body 🫶. this spec is based on the proposed solution in [1] and builds on it ✨.
Address Resolution is all about turning IP addresses into WW_PN (MAC address) and turning WW_PN into FC Port Identifiers (Port_ID) 🦋. ARP handles the first one and FARP handles the second one 💖.
an optional FARP mechanism can go straight from an IP address to FC Port_IDs. this is so useful for some upper layer applications 🧚.
InARP is another optional mechanism 💜. it resolves WW_PN and Port_ID to an IP address. it's helpful when a node has done a PLOGI with another node, so it knows its WW_PN and Port_ID, but it doesn't know its IP address yet 🥺.
3. IP and ARP Encapsulation 🌸
3.1 FC Frame Format
all FC frames have a standard format that's kinda like LAN 802.x protocols 🍓 (see Appendix E and F). the exact size of each frame changes depending on how big the variable fields are. the variable field goes from 0 to 2112-bytes, as you can see in the FC Frame Format in Fig. 1 👑.
+------+--------+-----------+----//-------+------+------+
| SOF |Frame |Optional | Frame | CRC | EOF |
| (4B) |Header |Header | Payload | (4B) | (4B) |
| |(24B) |<----------------------->| | |
| | | Data Field = (0-2112B) | | |
+------+--------+-----------+----//-------+------+------+
Fig. 1 FC Frame Formatthe Start of Frame (SOF) and End of Frame (EOF) are both 4-bytes long, and they act as frame delimiters 🦋.
the CRC is 4-bytes long. it uses the same 32-bit polynomial that FDDI uses, and it's specified in ANSI X3.139 Fiber Distributed Data Interface 🔥.
the Frame Header is 24-bytes long and has a bunch of fields for identifying and controlling the payload 🎀. some of the values and options for this field that matter for IP and ARP payloads are covered in Section 7 💅.
current FC Standards let you have up to 3 Optional Header fields [11]:
Network_Header(16-bytes)Association_Header(32-bytes)Device_Header(up to 64-bytes)
the IP and ARP FC Sequences SHALL carry only the Network_Header field, which is 16-bytes long. other types of optional headers SHALL NOT be used 🙈. the Network_Header is REQUIRED in all ARP packets, and in the first frame of a logical sequence carrying an IP payload, as described below 💖.
an application level payload like IP is called an Information Unit at the FC-4 Level 🌈. lower FC levels map this to a FC Sequence (see Appendix E.2 for a description of Sequences and Information Units) ✨. usually a Sequence has more than one frame. bigger user data gets segmented and reassembled using two methods: Sequence Count and Relative Offset [18] 🧚. with Sequence Count, data blocks are sent in frames with increasing sequence counts (modulo 65536), so it's pretty straightforward to find the first frame that has the Network_Header 🫶. with Relative Offset, some computation is required as frames arrive to find that first frame 🤓. the Sequence Count and Relative Offset field control information is carried in the FC Header 💅.
in FC, the physical order the frames show up in at a destination can be different from the order they were sent in, because they travel through an FC Network 😭.
when IP forms the FC Payload, only the first frame of the logical Sequence SHALL include the FC Network_Header 👑. Fig. 2 shows the logical First Frame and the logical subsequent frames 🦋. since frames can arrive out of order, detecting the first frame of the logical FC Sequence is necessary 💜.
ARP packets map to a single frame FC Sequence, and they SHALL always carry the FC Network_Header 🎀.
okay peep the definitions of FC Data Field and FC Frame Payload in Fig. 1 👀. the FC Data Field includes the FC Frame Payload and the FC Optional Header. the Frame Payload definition does NOT include the FC Optional Header 💅. one or more Frame Payloads together make the FC Sequence Payload, as shown in Fig 2 and discussed more in Sections 3.2 and 3.4 🌸. the FC Sequence Payload includes the mapped IP or ARP packet along with the LLC/SNAP headers 🍓.
First Frame of a Logical FC Sequence
---+------------+---------------------------+----------//----------+---
| FC Header | FC Network_Header | FC Sequence Payload |
---+------------+---------------------------+---------//-----------+---
Subsequent Frames of a Logical FC Sequence
--+-----------+--------------//----------------+--
| FC Header | Additional FC Sequence Payload |
--+-----------+-------------//-----------------+--
Fig. 2 FC Network_Header in a Frame Sequencethe SOF, CRC, EOF control fields and other optional headers were left out of the figure, just to keep it clean for us 🙈.
3.2 MTU
3.2.1 IP MTU
an FC Information Unit that's specific to each protocol, like IP, is defined in FC-4 ✨. this sets the upper bound on how much information can be transported 🦋.
each IP or ARP Packet gets mapped to a single FC Information Unit, which then gets mapped to a single FC Sequence. it's a one-to-one mapping between an IP or ARP packet and a FC Sequence 💖.
Fibre Channel limits a single Information Unit to 2^32-1, which is HUGE [2] 🔥. but since the Maximum Transmission Unit (MTU) size of an IPv4 packet never goes past 65,536-bytes, the mapped IPv4 size is WAY below that 2^32-1 limit 💅.
an IPv4 Packet includes the IP Payload and the IP Headers, both fixed and optional 🌈. the matching FC Sequence Payload includes the LLC/SNAP Header and the IPv4 packet 🧚.
as we said above, the biggest length allowed for an IPv4 Packet, including any optional headers and no matter what this standard says, is 65,536-bytes 👑. however, capping the IP MTU size at 65,280-bytes helps with buffer resource allocation at N_Ports, and it leaves room for up to 256-bytes of overhead 🎀. the FC Network_Header needs 16-bytes and the IEEE 802.2 LLC/SNAP header needs 8 bytes, so that leaves 232 bytes for future use 🫶.
All implementations SHALL restrict the IP MTU size to 65,280 bytes, and the matching FC Sequence Payload size to 65536-bytes 💜.
3.2.2 Maximally Minimum IPv4 Packet
for IP fragmentation and reassembly to work properly, every implementation of IP has to be able to carry a maximally minimum size IP packet without fragmentation 🥺. a maximally minimum size IP Packet is an IP Packet with an 8-byte payload (the smallest possible non-zero payload size for a fragment) and a 60-byte header (the biggest possible header, made of a 20-byte fixed part and a maximum size option field of 40-bytes) [17] 🤓.
All implementations SHALL support a FC Data Field of 92-bytes 💅. that covers 68-bytes of the maximally minimum sized IP Packet, 16-bytes of the FC Network_Header, and 8-bytes of the LLC/SNAP Header, which is required to support all of that 🌸.
3.2.3 ARP MTU
the ARP packet has a fixed size of 28-bytes 🍓. All implementations SHALL support a FC Data Field size of 52-bytes ✨. that's 28-bytes of an ARP Packet, 16-bytes of the FC Network_Header, and 8-bytes of the LLC/SNAP Header, which is required to support it 🧚. the minimum MTU requirement for ARP is already covered by the minimum MTU requirement for IP, but it's mentioned here for completeness 🫶.
the InARP packet is identical in size to the ARP, so the same MTU requirements apply 💖.
3.2.4 FC Data Field containing FARP Packet
the FARP Command is a FC Extended Link Service (ELS) command 🦋. it maps directly to the FC Data Field, without the LLC/SNAP or the FC Network_Header 💜. the FARP Command has a fixed size of 76-bytes 🎀. since FARP operates purely in the FC space, it doesn't put any special MTU requirements on this specification 👑.
3.3 FC Port and Node Network Addresses
FC devices are identified by Nodes and their Ports 🌈. a Node is a collection of one or more Ports, identified by a unique nonvolatile 64-bit World Wide Node name (WW_NN) 💅. each Port in a node is identified by a unique nonvolatile 64-bit World Wide Port name (WW_PN) and a volatile Port Identifier (Port_ID) 🔥.
Port_IDs are 24-bits long 🧚. an FC frame header carries a Source Port_ID (S_ID) and a Destination Port_ID (D_ID) 🫶. the Port_ID of a given port is volatile 🥺. (the mechanism(s) that let a Port_ID change in an FC topology are outside the scope of this document, so check Appendix D if you're curious 🤓.)
the FC Network_Header is normally optional in FC Standards, but it's REQUIRED in this specification 💖. an FC Network_Header carries the source and destination WW_PNs 💜. a WW_PN is made of a 60-bit Network Address and an upper 4-bit Network Address Authority (NAA) field, as shown in Fig. 3 ✨. the 4-bit NAA field is used to tell apart the various name registration authorities used to define the Network Address [2] 🦋.
in this specification, both the Source and Destination 4-bit NAA identifiers SHALL be set to binary '0001'. that means an IEEE 48-bit MAC address is in the lower 48 bits of the network address fields 🎀. the high order 12 bits in the network address fields SHALL be set to 0x0000 💅. the NAA field value of binary '0001' lets FC networks get bridged with other FC networks or traditional LANs 🌸.
+--------+---------------------------------------+
| D_NAA |Network_Dest_Address (High-order bits) |
|(4 bits)| (28 bits) |
+--------+---------------------------------------+
| Network_Dest_Address (Low-order bits) |
| (32 bits) |
+--------+---------------------------------------+
| S_NAA |Network_Source_Address(High-order bits)|
|(4 bits)| (28 bits) |
+--------+---------------------------------------+
| Network_Source_Address (Low-order bit) |
| (32 bits) |
+--------+---------------------------------------+
Fig. 3 Format of the Network_Header Field3.4. FC Sequence Payload Format 🎀
FC Payload with IP: okay so an FC Sequence Payload carrying an IP and ARP packet SHALL use the formats in Figs. 4 and 5 respectively. Both formats start with the 8-byte LLC/SNAP header, which is giving very organized energy 💅
+-----------------+-----------+------------+-------------//----------+
| LLC/SNAP Header | IP Header | Opt.IP Hdr.| IP Data |
| (8 bytes) | (20 bytes)| (40 bytes | (65280 -IP Header |
| | | Max) | - Opt. IP Hdr.) bytes |
+-----------------+-----------+------------+-------------//----------+
Fig. 4 Format of FC Sequence Payload carrying IPFC Sequence Payload with ARP: as we said earlier, FC frames in the same Sequence can arrive out of order over a Fabric 🌀 So if the Relative Offset method is used to identify FC Sequence Payload fragments, then the IP Header MUST appear in the frame that has a relative offset of 0. No skipping that part, bestie 🫶
+-----------------+-------------------+
| LLC/SNAP Header | ARP Packet |
| (8 bytes) | (28 bytes) |
+-----------------+-------------------+
Fig. 5 Format of FC Sequence Payload carrying ARPFC Sequence Payload with FARP: FARP Protocol commands map straight onto the Frame Sequence Payload, and they're 76 bytes long 🧚 There's no LLC/SNAP Header and no FC Network_Header here, so the FC Data Field size is literally just the FC Sequence Payload. Simple and iconic ✨
LLC:
A Logical Link Control (LLC) field plus a Sub Network Access Protocol (SNAP) field is how you identify routed and bridged non-OSI protocol PDUs. It's defined by IEEE 802.2 and applied to IP in [8]. In LLC Type 1 operation (aka unacknowledged connectionless mode), the LLC header is 3 bytes long. It has a 1-byte Destination Service Access Point (DSAP) field, a 1-byte Source Service Access Point (SSAP) field, and a 1-byte Control field, as shown in Fig. 6 💜
+----------+----------+----------+
| DSAP | SSAP | CTRL |
| (1 byte) | (1 byte) | (1 byte) |
+----------+----------+----------+
Fig. 6 LLC FormatThe LLC's DSAP and SSAP values of 0xAA mean an IEEE 802.2 SNAP header follows. A CTRL value of 0x03 specifies an Unnumbered Information Command PDU. In this specification the LLC Header value SHALL be set to 0xAA-AA-03. Other DSAP/SSAP values indicate support for other protocols and SHALL NOT be used in this specification 🚫
SNAP:
The SNAP Header is 5 bytes long. It has a 3-byte Organizationally Unique Identifier (OUI) field and a 2-byte Protocol Identifier (PID), as shown in Fig. 7 🌸
+------+------+-------+------+------+
| OUI | PID |
| ( 3 bytes) | (2 bytes) |
+------+------+-------+------+------+
Fig. 7 SNAP FormatSNAP was invented to "encapsulate" LAN frames within the payload 🍓 A SNAP OUI value of 0x00-00-00 says the PID is an EtherType (i.e., a routed non-OSI protocol). A SNAP OUI value of 0x00-80-C2 indicates Bridged Protocols.
With the OUI set to 0x00-00-00, a SNAP PID value of 0x08-00 indicates IP, and a PID value of 0x08-06 indicates ARP (or InARP). The complete LLC/SNAP Header is shown in Fig. 8 🦋
+-----------+----------+----------+-------+-------+-------+-------+------+
| DSAP | SSAP | CTRL | OUI | PID |
| (1 byte) | (1 byte) | (1 byte) | ( 3 bytes) | (2 bytes |
+-----------+----------+----------+-------+-------+-------+-------+------+
Fig. 8 LLC/SNAP Header3.5. Bit and Byte Ordering 🌈
IP or ARP Packets are mapped to the FC-4 Level using big endian byte ordering, which matches the standard network byte order or canonical form [20]. The FC-4 Payload maps to the FC-2 Level with no change in order.
FC-1 Level defines how data gets encoded before transmission and decoded on reception. It encodes 8-bit bytes into 10-bit transmission characters, which helps the serial data stream transmit well ⭐ In Fibre Channel, data fields are aligned on word boundaries (see Appendix E). A word in FC is 4 bytes, or 32 bits. After the 8-bit to 10-bit encoding, the transmission word is 40 bits.
Data words, or Ordered Sets (special FC-2 Level control words), go from the FC-2 Level to the FC-1 Level with no change in order. Bytes within a word are sent Most Significant Byte first, down to Least Significant Byte. Bits within each byte are sent Least Significant Bit first, up to Most Significant Bit 🔥
4. ARP ✨
4.1. Address Resolution 💖
Address Resolution in this specification is mainly about linking IP addresses with FC Port addresses. As we covered earlier, FC device ports have two kinds of addresses:
- a non-volatile unique 64-bit address called World Wide Port_Name (WW_PN)
- a volatile 24-bit address called a Port_ID
So the Address Resolution mechanism needs two levels of mapping:
- A mapping from the IP address to the WW_PN (i.e., IEEE 48-bit MAC address)
- A mapping from the WW_PN to the Port_ID (see Appendix G for a definition of Port_ID)
The address resolution problem gets extra spicy because the Port_ID is volatile, and the second mapping MUST be valid before use. The validation process can also differ depending on the network topology in use. Appendix D covers validation for the different FC topologies 🧩
Architecturally, the first level of mapping and control operation is handled by the Address Resolution Protocol (ARP), and the second level is handled by the FC Address Resolution Protocol (FARP). FARP is described in Section 5 🌷
Other optional FARP mechanisms that map an IP address straight to a Port_ID, or a WW_NN to a Port_ID, are described in Appendix A. The Inverse Address Resolution Protocol (InARP) is another optional mechanism, and it resolves WW_PN and Port_IDs to IP addresses. InARP is described in Appendix B 💜
4.2. ARP Packet Format 🎀
The Address Resolution Protocol (ARP) given in [9] was designed as a general purpose protocol. It works with many network technologies and many upper layer protocols. Fig 9 shows the ARP packet format based on [9], where the upper layer protocol uses a 4-octet protocol (IP) address and the network technology uses a 6-octet hardware (MAC) address 🫶
The ARP uses two packet types, Request and Reply, and each packet is 28 bytes long in this specification. The ARP Packet fields are common to both ARP Requests and ARP Replys.
The LLC/SNAP encapsulated ARP Request Packet is mapped to an FC Broadcast Sequence. How the broadcast actually happens depends on the FC topology, and that's discussed later in this section. Compliant ARP Request Broadcasts SHALL include Network_Headers.
The LLC/SNAP encapsulated ARP Reply Packet is mapped to an FC Sequence. Compliant ARP Replys SHALL include Network_Headers.
Note that in all the discussions to follow, the WW_PN and the 48-bit MAC address conceptually mean the same thing 👑
The 'HW Type' field SHALL be set to 0x00-01.
Technically, the correct HW Type value should be 0x00-06 according to RFC 1700, which indicates IEEE 802 networks. As a practical matter, though, a HW Type value of 0x00-06 is known to cause rejections from some Ethernet end stations when FC is bridged to Ethernet. Translational bridges are normally expected to change this field from Type 6 to 1 and vice versa under these configurations, but many don't. That's why the Type Code is set to 1 rather than 6. However, both HW Type values of 0x00-01 and 0x00-06 SHALL be accepted 🙈
The 'Protocol' field SHALL be set to 0x08-00, indicating IP protocol.
The 'HW Addr Length' field SHALL be set to 0x06, indicating 6 bytes of HW address.
The 'Protocol Addr Length' field SHALL be set to 0x04, indicating 4 bytes of IPv4 address.
The 'Operation' Code field SHALL be set as follows:
0x00-01 for ARP Request
0x00-02 for ARP ReplyThe 'HW Addr of Sender' field SHALL be the 6-byte IEEE MAC address of the sender. It's either the Requester (ARP Request) or the Responder (ARP Reply) address 🦋
The 'Protocol Addr of Sender' field SHALL be the 4-byte IP address of the Requester (ARP Request) or of the Responder (ARP Reply).
The 'HW Addr of Target' field SHALL be set to zero during an ARP Request, and to the 6-byte MAC address of the Requester (ARP Request) in an ARP Reply.
The 'Protocol Addr of Target' field SHALL be set to the 4-byte IP address of the Responder (ARP Reply) in an ARP Request, and to the 4-byte IP address of the Requester (ARP Request) in an ARP Reply.
+-------------------------+
| HW Type | 2 bytes
+-------------------------+
| Protocol | 2 bytes
+-------------------------+
| HW Addr Length | 1 byte
+-------------------------+
| Protocol Addr Length | 1 byte
+-------------------------+
| Op Code | 2 bytes
+-------------------------+
| HW Addr of Sender | 6 bytes
+-------------------------+
| Protocol Addr of Sender | 4 bytes
+-------------------------+
| HW Addr of Target | 6 bytes
+-------------------------+
| Protocol Addr of Target | 4 bytes
+-------------------------+
Total 28 bytes
Fig. 9 ARP Packet Format4.3. ARP Layer Mapping and Operation 🧚
Whenever an FC port wants to send IP data to another FC port, these steps happen:
- The source port should first check its local mapping tables to find the <destination IP address, destination WW_PN>.
- If such a mapping is found, the source sends the IP data to the port whose WW_PN address was found in the table.
- If no such mapping is found, the source sends an ARP Request broadcast to its connected FC network, hoping for a reply from the correct destination along with its WW_PN.
- When an ARP Request Broadcast frame reaches a node with the matching IP address, that node generates an ARP Reply. Since the ARP Reply must be addressed to a specific destination Port_ID, the FC layer mapping between the WW_PN and the Port_ID (of the ARP Request originator) MUST be valid before the reply is sent 💅
- If no node has the matching IP address, the result is silent behavior 🤫
4.4. ARP Broadcast in a Point-to-Point Topology 🌸
The ARP Request (Broadcast) and Reply mechanism described above still applies, even though only one node receives the ARP Request 🦋
4.5 ARP Broadcast in a Private Loop Topology
okay so in a private loop, the ARP Request Broadcast frame gets sent using the broadcast method from the FC-AL [7]standard 🔁✨
- First up, the source port sends an Open Broadcast Replicate primitive
OPN(fr)signal 📡. This tells all the ports in the loop (except itself) to replicate the frames they receive while they check the frame header'sDestination_IDfield 🫶 - Then the source port removes this
OPN(fr)signal once it comes back around to itself 🔄 - Now the loop is ready for the ARP broadcast 🎀 The source sends the ARP Request as a single-frame Broadcast Sequence in a Class 3 frame, with these FC Header
D_IDfield andF_CTLbit settings:Destination ID <Word 0, bit 0:23>: D_ID = 0xFF-FF-FFSequence Initiative <Word 2, bit23>: SI=0Last Sequence <Word 2, bit 20>: LS=1End Sequence <Word 2, bit 19>: ES=1
- A compliant ARP Broadcast Sequence frame SHALL include the
Network_Headerwith destination MAC address set to0xFF-FF-FF-FF-FF-FFand withNAA = b'0001'💅 - The destination port that recognizes its IP address in the ARP Request packet SHALL respond with an ARP Reply 💖
4.6 ARP Broadcast in a Public Loop Topology
here's the flow when a port is set up in a public loop 🌈
- A public loop device attached to a fabric through a FL_Port MUST NOT use the
OPN(fr)signal primitive 🙅♀️ Instead, it sends the broadcast sequence to the FL_Port atAL_PA = 0x00 - The FC Fabric propagates the broadcast to all other ports, including the FL_Port the broadcast arrived on. That covers all F_Ports and other FL_Ports 🌸
- On each FL_Port, the fabric propagates the broadcast by first using the primitive signal
OPNfr, so the loop is prepped to receive the broadcast sequence 🧚 - A Broadcast Sequence is now sent on all ports (all FL_Ports and F_Ports) in a Class 3 frame, with:
Destination ID <Word 0, bit 23:0>: D_ID = 0xFF-FF-FFSequence Initiative <Word 2, bit23>: SI=0Last Sequence <Word 2, bit 20>: LS=1End Sequence <Word 2, bit 19>: ES=1
- A compliant ARP Broadcast Sequence frame SHALL include the
Network_Headerwith destination MAC address set to0xFF-FF-FF-FF-FF-FFand withNAA = b'0001'✨ - The destination port that recognizes its IP address in the ARP Request packet SHALL respond with an ARP Reply 🦋
4.7 ARP Operation in a Fabric Topology
fabric topology is giving easy mode, ngl 💁♀️
- Nodes directly attached to the fabric do not require the
OPN(fr)primitive signal 🫧 - A Broadcast Sequence is now sent on all ports (all FL_Ports and F_Ports) in a Class 3 frame, with:
Destination ID <Word 0, bit 23:0>: D_ID = 0xFF-FF-FFSequence Initiative <Word 2, bit23>: SI=0Last Sequence <Word 2, bit 20>: LS=1End Sequence <Word 2, bit 19>: ES=1
- A compliant ARP Broadcast Sequence frame SHALL include the
Network_Headerwith destination MAC address set to0xFF-FF-FF-FF-FF-FFand withNAA = b'0001'💜 - The destination port that recognizes its IP address in the ARP packet SHALL respond with an ARP Reply 👑
5. FARP 🧚
5.1 Scope
okay bestie, the WW_PN to Port_ID mapping is its own thing. It doesn't depend on ARP, and it's way more tied to the details of the FC protocols 🫶 Two formal mechanisms can build and keep WW_PN to Port_ID tables: the Name Server and the FC Address Resolution Protocol (FARP) 🎀
FARP is a method that uses Extended Link Service (ELS) commands to resolve <WW_PN, Port_ID> mappings. It's especially handy when the Login table entries at a node expire and there's no Name Server around 🥺 Describing the Name Server is outside the scope of this document (see [14]) 📚
FARP also picked up extra address matching mechanisms that resolve <WW_NN, Port_ID> and <IP addr., Port_ID> mappings. These extras are optional and described in Appendix A. Direct IP address to Port_ID mapping is super useful when you can't see the MAC address 🌈
Other, less formal FC Layer Mapping mechanisms are described in Appendix C 💅
Port_IDs are volatile, so every mapped Port_ID MUST be valid before use, no exceptions 🚨 Plenty of events can invalidate a mapping, and Appendix D covers the conditions where that validation is required ✨
5.2 FARP Overview
FARP runs on two ELS commands, FARP-REQ and FARP-REPLY 🦋
Note: In the following discussion, 'Requester' means the node issuing the FARP-REQ ELS message, and 'Responder' means the node replying to the request by sending the FARP-REPLY command. 🫶
The FARP-REQ ELS Broadcast Request command is used to retrieve a specific node's current Port_ID, given its unique WW_PN. That Port_ID comes back in a FARP-REPLY unicast command 💖
The FARP-REQ may tell the Responder to:
- Perform only a Login with it (Requester) or,
- Send only a
FARP-REPLYor, - Perform a Login and send a
FARP-REPLY.
No sequence initiative is transferred with the FARP-REQ, so no Reply (ACCEPT or REJECT) follows this command 🙈
Since a Sequence Initiative is transferred with the FARP-REPLY, either an ACCEPT or a REJECT follows this command as a response 💜
Receiving a FARP-REQ means a higher level entity at the responding node has to send a FARP-REPLY or perform a Port Login 👑
You do not have to be logged in to issue a FARP Request. You also don't have to be logged in to the FARP Requester to issue a FARP-REPLY 🌸
The FARP Protocol Steps:
FARP-REQ (ELS broadcast) Request Sequence
(No Reply Sequence)
FARP-REPLY (ELS command) Sequence
Accept/Reject Reply SequenceThe FARP Protocol Format [2] and Size: FT_1, 76-bytes fixed size 🍓
The FARP Protocol Addressing:
- In a
FARP-REQ, theS_IDin the FC Header designates the Requester's Port ID. TheD_IDin the FC Header is the broadcast identifier0xFF-FF-FF📣 - In a
FARP-REPLY, theS_IDin the FC Header designates the Responder's Port_ID. TheD_IDin the FC Header is the Requester's Port_ID 🎀
5.3. FARP Command Format 💅
okay so FARP-REQ and FARP-REPLY are literal twins 👯♀️ same format, same 76-bytes fixed size, same fields. the only difference is the command code they use. tables below, bestie 🎀
+---------------------------------------------------------------------+
| FARP-REQ Command |
+-------------------------------------+---------+---------------------+
| Field | Size | Remarks |
| | (Bytes) | |
+-------------------------------------+---------+---------------------+
| 0x54-00-00-00 | 4 | Request Command Code|
+-------------------------------------+---------+---------------------+
| Match Address Code Points | 1 | Indicates Address |
| | | Matching Mechanism |
+-------------------------------------+---------+---------------------+
| Port_ID of Requester | 3 | Supplied by |
| | | Requester = |
| | | S_ID in FC Header |
+-------------------------------------+---------+---------------------+
| Responder Flags | 1 | Response Action to |
| | | be taken |
+-------------------------------------+---------+---------------------+
| Port_ID of Responder | 3 | Set to 0x00-00-00 |
+-------------------------------------+---------+---------------------+
| WW_PN of Requester | 8 |Supplied by Requester|
+-------------------------------------+---------+---------------------+
+ WW_NN of Requester | 8 |OPTIONAL; |
| | |See Appendix A |
+-------------------------------------+---------+---------------------+
| WW_PN of Responder | 8 |Supplied by Requester|
+-------------------------------------+---------+---------------------+
| WW_NN of Responder | 8 |OPTIONAL; see App. A |
+-------------------------------------+---------+---------------------+
| IP Address of Requester | 16 |OPTIONAL; see App. A |
+-------------------------------------+---------+---------------------+
| IP Address of Responder | 16 |OPTIONAL; see App. A |
+-------------------------------------+---------+---------------------+
+---------------------------------------------------------------------+
| FARP-REPLY Command |
+-------------------------------------+---------+---------------------+
| Field | Size | Remarks |
| | (Bytes) | |
+-------------------------------------+---------+---------------------+
| 0x55-00-00-00 | 4 | Reply Command Code |
+-------------------------------------+---------+---------------------+
| Match Address Code Points | 1 | Not Used and |
| | | Unchanged from the |
| | | FARP-REQ |
+-------------------------------------+---------+---------------------+
| Port_ID of Requester | 3 | Extracted from |
| | | FARP-REQ |
+-------------------------------------+---------+---------------------+
| Responder Flags | 1 | Not Used and |
| | | Unchanged from the |
| | | FARP-REQ |
+-------------------------------------+---------+---------------------+
| Port_ID of Responder | 3 | Supplied by |
| | | Responder = |
| | | S_ID in FC Header |
+-------------------------------------+---------+---------------------+
|WW_PN of Requester | 8 |Supplied by Requester|
+-------------------------------------+---------+---------------------+
|WW_NN of Requester | 8 |OPTIONAL; see App. A |
+-------------------------------------+---------+---------------------+
|WW_PN of Responder | 8 |Supplied by Requester|
+-------------------------------------+---------+---------------------+
|WW_NN of Responder | 8 |OPTIONAL; see App. A |
+-------------------------------------+---------+---------------------+
|IP Add. of Requester | 16 |OPTIONAL; see App. A |
+-------------------------------------+---------+---------------------+
|IP Address of Responder | 16 |OPTIONAL; see App. A |
+-------------------------------------+---------+---------------------+here's the tea on each address field 🫖
Port_ID of Requester: this is the 24-bit Port_ID sitting in the S_ID field of the FC Header of a FARP-REQ 🦋 the Requester supplies it in the FARP-REQ, and it gets kept (retained) in the FARP-REPLY.
Port_ID of Responder: this is the 24-bit Port_ID sitting in the S_ID field of the FC Header of a FARP-REPLY. it SHALL be set to 0x00-00-00 in a FARP-REQ, and the Responder supplies it in a FARP-REPLY.
WW_PN: this one gets used with the Match Address Code Points b'001', b'011', b'101, and b'111' (see the Match Address Code Point Table in the next section). the Requester supplies the unique 8-byte WW_PN of the Requester and of the Responder. it gets retained in the FARP-REPLY.
WW_NN: this one is used with Match Address Code Points b'010', b'011', b'110', and b'111', which are all optional. the full scoop on how it works lives in Appendix A. when the WW_NN field isn't used, it SHALL be either set to '0' or a valid non-zero address.
IPv4: this one is used with Match Address Code Points b'100', b'101', b'110', and b'111', which are all optional. Appendix A has the whole story. when the IP Address field isn't used, it SHALL be either set to '0' or a valid IP address. a valid IP address is the 32-bit IPv4 Address with the upper 96 bits set to '0' 💖
5.4. Match Address Code Points 🎯
so every time a FARP-REQ Broadcast ELS comes in, the recipients match one or more addresses based on the encoded bits of the "FARP Match Address Code Points" field in the table below. this section covers how FARP works when the Match Address Code Point is b'001'. the other code points are OPTIONAL and get discussed in Appendix A. also, the upper 5 bits of the Match Address Code Point byte are unused, and nobody has defined what they're for yet 🙈
+------------------------------------------------------------------+
| Match Address Code Points |
+------------------------------------------------------------------+
| LSBits | Bit name | Action |
+-----------+--------------------+---------------------------------+
| 000 | Reserved | |
+-----------+--------------------+---------------------------------+
| 001 | MATCH_WW_PN | If 'WW_PN of Responder' = |
| | | Node's WW_PN then respond |
+-----------+--------------------+---------------------------------+
| 010 | MATCH_WW_NN | OPTIONAL; see Appendix A |
+-----------+--------------------+---------------------------------+
| 011 | MATCH_WW_PN_NN | OPTIONAL; see Appendix A |
+-----------+--------------------+---------------------------------+
| 100 | MATCH_IPv4 | OPTIONAL; see Appendix A |
+-----------+--------------------+---------------------------------+
| 101 | MATCH_WW_PN_IPv4 | OPTIONAL; see Appendix A |
+-----------+--------------------+---------------------------------+
| 110 | MATCH_WW_NN_IPv4 | OPTIONAL; see Appendix A |
+-----------+--------------------+---------------------------------+
| 111 | MATCH_WW_PN_NN_IPv4| OPTIONAL; see Appendix A |
+-----------+--------------------+---------------------------------+okay so when a node gets a FARP-REQ with Code Point b'001', it checks its WW_PN against the one in the 'WW_PN of Responder' field of the FARP-REQ command. if they match, the node sends a response based on what the FARP Responder Flag says (see the table below) 🔥
the WW_NN and IPv4 address fields aren't used with the b'001' Code Point. they SHALL be set to '0' or a valid address, either by the Requester, or by the Requester and the Responder 🫶
and one last thing: there can be utmost one FARP-REPLY per FARP-REQ. that's the rule, no exceptions 💅
5.5. Responder Flags 🚩
the Responder Flags tell the Responder what to do if the Match Address Code Points check comes back successful. it's an 8-bit field (bits 0-7), and it's defined in the table below. only a FARP-REQ uses this field, and it stays unchanged in the FARP-REPLY. if no bits are set, the Responder takes no action 😌
+----------+-------------------------------------------------------+
| | FARP Responder Flag |
+----------+----------------+--------------------------------------+
| Bit | Bit Name | Action |
| Position | | |
+----------+----------------+--------------------------------------+
| 0 | INIT_P_LOGI | Initiate a P_LOGI to the Requester |
+----------+----------------+--------------------------------------+
| 1 | INIT_REPLY | Send FARP_REPLY to Requester |
+----------+----------------+--------------------------------------+
| 2 to 7 | Reserved | |
+----------+----------------+--------------------------------------+if INIT_P_LOGI is set, a Login gets performed with the port identified by the "Port_ID of Requester" field 🔑
if INIT_REPLY is set, a FARP-REPLY gets sent to the Port identified by the "Port_ID of Requester" field 📨
if both bits are set at the same time, then both Actions happen. double the action, bestie 👯
all other bit patterns are undefined right now and are reserved for possible future use 🌸
5.6. FARP Support Requirements 📋
the Responder action (FARP-REPLY and/or Port Login) for a successful MATCH_WW_PN is always REQUIRED. if there's no address match, then silent behavior is the move 🤫
support for all the other Match Address Code Points is OPTIONAL, and it's totally valid for the Responder to stay silent when it doesn't support them. recipients of the FARP-REQ ELS SHALL NOT issue a Service Reject (LS_RJT) just because FARP OPTIONAL mechanisms aren't supported. no drama allowed 🙅♀️
in every case, if there are no matches, silent behavior is specified 🤐
now here's the sneaky part 👀 if an implementation sends a FARP-REQ with a Match Address Code Point that is OPTIONAL, doesn't get a response, and hasn't found the Responder's Port_ID by other means (for example, a prior FARP-REQ with other Code Points), then it SHALL reattempt the FARP-REQ with the MATCH_WW_PN Code Point. second chances, iykyk 🔁
and finally, getting multiple FARP Replies for a single FARP-REQ should normally never happen. it's beyond the scope of this document to spell out the conditions where this error might pop up or what the fix ought to be 💀
6. Exchange Management ✨
6.1 Exchange Origination 💖
Okay bestie, so FC Exchanges SHALL be established to move data between ports ✨ Frames on IP exchanges SHALL NOT carry Sequence Initiative 🙅♀️ If you want the deep dive on FC Exchanges, go read Appendix E 📖
6.2 Exchange Termination 🌸
Okay so, the recommendations in Appendix F, Section F.1, "Reliability in Class 3", are the one exception here 🫶 Apart from that, how exchanges get aged out or expired (by activity, timeout, or some other method) is outside the scope of this document 🙈
Either port can terminate an Exchange 💅 The Exchange Originator can end one by setting the LS bit, following the normal FC standard FC-PH [2] rules. This specification prohibits the use of the NOP ELS with LS set for Exchange termination 🚫 no shortcuts, periodt.
Exchanges can also be torn down by the Exchange Originator or the Exchange Responder using the ABTS_LS protocol ✨ Using ABTS_LS for terminating aged Exchanges or for error recovery is outside the scope of this document, so don't look for it here 🦋
Logging out to terminate IP Exchanges is discouraged 😬 because it can end active Exchanges on other FC-4s too.
7. Summary of Supported Features 👑
Note: "Settable" means support is as specified in the relevant standard. All other key words are as defined earlier in this document 🧚
7.1 FC-4 Header 🎀
+--------------------------------------------------------------------+
| Feature | Support | Notes |
+--------------------------------------------------------------------+
| Type Code ( = 5) ISO8802-2 LLC/SNAP | REQUIRED | 2 |
| Network_Headers | REQUIRED | 3 |
| Other Optional Headers | MUST NOT | |
+--------------------------------------------------------------------+Notes:
- This table only covers FC-4 related data, like IP and ARP packets 💕 It does not cover link services and other non-FC-4 sequences (PLOGI, for example) that have to happen for normal operation.
- The TYPE field in the FC Header (Word 2 bits 31-24) MUST indicate ISO 8802-2 LLC/SNAP Encapsulation (Type 5) 🫧 This revision focuses only on the stuff needed to run IP and ARP over FC. Everything else is outside the scope of this document, including full support for IEEE 802.2 LLC.
- The DF_CTL field (Word 3, bits 23-16 of FC-Header) MUST indicate the presence of a Network_Header (0010 0000) on the First logical Frame of FC-4 Sequences ✨ It should not indicate a Network_Header on any later frames of the Sequence.
7.2 R_CTL 🦋
R_CTL in FC-Header: Word 0, bits 31-24
+--------------------------------------------------------------------+
| Feature | Support | Notes |
+--------------------------------------------------------------------+
| Information Category (R_CTL Routing): | | |
| | | |
| FC-4 Device Data | REQUIRED | 1 |
| Extended Link Data | REQUIRED | |
| FC-4 Link Data | MUST NOT | |
| Video Data | MUST NOT | |
| Basic Link Data | REQUIRED | |
| Link Control | REQUIRED | |
| | | |
| R_CTL information : | | |
| | | |
| Uncategorized | MUST NOT | |
| Solicited Data | MUST NOT | |
| Unsolicited Control | REQUIRED | |
| Solicited Control | REQUIRED | |
| Unsolicited Data | REQUIRED | 1 |
| Data Descriptor | MUST NOT | |
| Unsolicited Command | MUST NOT | |
| Command Status | MUST NOT | |
+--------------------------------------------------------------------+Notes:
- This is REQUIRED for FC-4 (IP and ARP) packets 🌈
- The routing bits of the R_CTL field MUST indicate Device Data frames (0000)
- The Information Category of the R_CTL field MUST indicate Unsolicited Data (0100)
7.3 F_CTL 💜
F_CTL in FC-Header: Word 2, bits 23-0
+--------------------------------------------------------------------+
| Feature | Support | Notes |
+--------------------------------------------------------------------+
| Exchange Context | Settable | |
| Sequence Context | Settable | |
| First / Last / End Sequence (FS/LS/ES) | Settable | |
| Chained Sequence | MUST NOT | |
| Sequence Initiative (SI) | Settable | 1 |
| X_ID Reassigned / Invalidate | MUST NOT | |
| Unidirectional Transmit | Settable | |
| Continue Sequence Condition | REQUIRED | 2 |
| Abort Seq. Condition -continue and single Seq.| REQUIRED | 3 |
| Relative Offset - Unsolicited Data | Settable | 4 |
| Fill Bytes | Settable | |
+--------------------------------------------------------------------+Notes
- For FC-4 frames, each N_Port SHALL have a dedicated OX_ID for sending data to each N_Port in the network, and a dedicated RX_ID for receiving data from each N_Port as well 🫶 Exchanges are used in a unidirectional mode, so setting Sequence Initiative isn't valid for FC-4 frames. It is valid when using Extended Link Services ✨
- This field is required to be 00, meaning no information 🙈
- The sequence error policy is requested by an exchange originator in the F_CTL Abort Sequence Condition bits of the first data frame of the exchange. For Classes 1 and 2, the ACK frame is required to be "continuous sequence" 💅
- Relative offset is prohibited on all other types (Information Category) of frames 🚫
7.4 Sequences 🍓
+---------------------------------------------------------------------+
| Feature | Support |Notes |
+---------------------------------------------------------------------+
| Class 2 open Sequences / Exchange | 1 | 1 |
| Length of Seq. not limited by end-to-end credit | REQUIRED | 2 |
| IP and ARP Packet and FC Data Field sizes | REQUIRED | 3 |
| Capability to receive Sequence of maximum size | OPTIONAL | 4 |
| Sequence Streaming | MUST NOT | 5 |
| Stop Sequence Protocol | MUST NOT | |
| ACK_0 support | OPTIONAL | 6 |
| ACK_1 support | REQUIRED | 6 |
| ACK_N support | MUST NOT | |
| Class of Service for transmitted Sequences | Class | 7 |
| | 1, 2, or 3 | |
| Continuously Increasing Sequence Count | OPTIONAL | 8, 9 |
+---------------------------------------------------------------------+Notes:
- Only one active sequence per exchange is optional 🌷
- A Sequence Initiator SHALL be capable of transmitting Sequences with more frames than the available credit that a Sequence recipient indicated at Login 💫 FC-PH [2] end-to-end flow control rules will be followed when transmitting such Sequences.
- Sizes, the fun part 📏
- a) The IP MTU size is 65280-bytes, and the resulting FC Sequence Payload size is 65536-bytes.
- b) The Maximally Minimum IP Packet size is 68-bytes, and the resulting FC Data Field size is 92-bytes.
- c) The ARP (and InARP) Packet size is 28-bytes, and the resulting FC Data Field size is 52-bytes.
- Some OS environments may not handle the max Sequence Payload size of 65536 😅 It is up to the administrator to configure the Max size for all systems.
- All class 3 sequences are assumed to be non-streamed.
- This only applies to Class 1 and 2. ACK_1 is the default, and ACK_0 is used if the Sequence recipient indicates it at Login ✨
- The administrator configured class of service is used, except where otherwise specified (e.g. Broadcasts are always sent in Class 3) 🦋
- Review Appendix F, "Reliability in Class 3" 👀
- The first frame of the first sequence of a new Exchange MUST have SEQ_CNT = 0 [2] 🎯
7.5 Exchanges 🧚♀️
+--------------------------------------------------------------------+
| Feature | Support | Notes |
+--------------------------------------------------------------------+
| X_ID interlock support | OPTIONAL | 1 |
| OX_ID=FFFF | MUST NOT | |
| RX_ID=FFFF | OPTIONAL | 2 |
| Action if no exchange resources available | P_RJT | 3 |
| Long Lived Exchanges | OPTIONAL | 4 |
| Reallocation of Idle Exchanges | OPTIONAL | |
+--------------------------------------------------------------------+Notes:
- This only applies to Classes 1 and 2, and it's supported by the Exchange Originator 🤝 A Port SHALL be capable of interoperating with another Port that requires X_ID interlock. In those cases, the Exchange Originator facility within the Port SHALL use the X_ID Interlock protocol.
- An Exchange Responder is not required to assign RX_IDs. If an RX_ID of FFFF is assigned, it identifies Exchanges based only on S_ID / D_ID / OX_ID 🌈
- In Classes 1 and 2, a Port SHALL reject a frame that would create a new Exchange with a P_RJT containing the reason code "Unable to establish Exchange" 🙅♀️ In Class 3, the frame would be dropped.
- When an Exchange is created between 2 Ports for IP/ARP data, it stays active while the ports are logged in with each other 💖 An Exchange SHALL NOT transfer Sequence Initiative (SI). Broadcasts and ELS commands may use short-lived Exchanges.
7.6 ARP and InARP ✨
Okay bestie, time for the ARP and InARP table 💅 Here's how the features and their support levels line up:
+--------------------------------------------------------------------+
| Feature | Support | Notes |
+--------------------------------------------------------------------+
| ARP Server Support | MUST NOT | 1 |
| Response to ARP requests | REQUIRED | 2 |
| Class of Service for ARP requests | Class 3 | 3 |
| Class of Service for ARP replies | Class | 4 |
| | 1, 2, or 3 | |
| Response to InARP requests | OPTIONAL | |
| Class of Service for InARP requests/replies | Class | |
| | 1, 2 or 3 | 5 |
+--------------------------------------------------------------------+Notes, because the details matter 🫶
- Well-known Address
FFFFFCis not used for ARP requests, and frames from it are not considered to be ARP frames. Broadcast support is REQUIRED for ARP. Non-negotiable, no cap 🔥 - The IP Address is mapped to a specific MAC address with ARP. That's the whole vibe 🦋
- An ARP request is a Broadcast Sequence, so Class 3 is always used. It's giving consistency 💜
- An ARP reply is a normal Sequence, so the administrator configured class of service is used. Bestie, the admin gets the final say here 🎀
- An InARP Request or Reply is a normal Sequence, so an administrator configured class of service is used. Same energy as note 4 🌸
7.7 Extended Link Services (ELS) 💖
Next up is the ELS table, and honestly it's the main character of this section 👑
+--------------------------------------------------------------------+
| Feature | Support | Notes |
+--------------------------------------------------------------------+
| Class of service for ELS commands / responses | Class | |
| | 1,2 or 3 | 1 |
| Explicit N-Port Login | REQUIRED | |
| Explicit F-Port Login | REQUIRED | |
| FLOGI ELS command | REQUIRED | |
| PLOGI ELS command | REQUIRED | |
| ADISC ELS command | REQUIRED | |
| PDISC ELS command | OPTIONAL | 2 |
| FAN ELS command | REQUIRED | 5 |
| LOGO ELS command | REQUIRED | |
| FARP-REQ/FARP-REPLY ELS commands | REQUIRED | 3 |
| Other ELS command support | OPTIONAL | 4 |
+-----------------------------------------------+------------+-------+Notes 🧚
- The administrator configured class of service is used. Hi admin again 🙈
- PDISC shall not be used as a Requester; ADISC shall be used instead. As a Responder, an implementation may need to respond to both ADISC and PDISC for compatibility with other specifications. So be the ADISC girlie, but be ready to answer PDISC too for compatibility 💅
- Responder Action, meaning FARP-REPLY and/or Port Login, for a successful MATCH_WW_PN is always REQUIRED. Support for all other match Address Codes Points is a silent behavior from the Responder is valid when it is not supported. Recipients of the FARP-REQ ELS shall not issue a Service Reject (LS_RJT) if FARP is not supported. Quiet is valid, no drama needed 🤫
- If other ELS commands are received, an LS_RJT may be sent. NOP is not required by this specification, and shall not be used as a mechanism to terminate exchanges. Not NOP, bestie, that's not its job 🙅♀️
- Required for FL_Ports 🌈
7.8 Login Parameters 🍓
Unless explicitly noted here, a compliant implementation shall use the login parameters as described in [4]. So if it isn't called out below, you just follow [4] ✨
7.8.1 Common Service Parameters - FLOGI
- FC-PH Version, lowest version may be
0x09to indicate 'minimum 4.3'. - You can't use
BB_Credit=0for N_Port on a switched Fabric (F_Port). Zero credits on a switch? Absolutely not 💀
7.8.2 Common Service Parameters - PLOGI
- FC-PH Version, lowest version may be
0x09to indicate 'minimum 4.3'. Same iconic move as FLOGI 💜 - You can't use
BB_Credit=0for N_Port in a Point-to-Point configuration. - Random Relative Offset is optional. Totally your call 🦋
- Note that the 'Receive Data Field Size' fields specified in the PLOGI represent both optional headers and payload. Both count, so don't forget either one 🎀
- The MAC Address can therefore be extracted from the 6 lower bytes of the WW_PN field (when the IEEE 48-bit Identifier format is chosen as the NAA) during PLOGI or ACC payload exchanged during Fibre Channel Login [2]. Such a clever trick, honestly obsessed 😭
- The MAC Address can also be extracted from the WW_PN field in the Network_Header during ADISC (and ADISC ACC), or PDISC (and PDISC ACC). Two places to find it, iconic 👑
7.8.3 Class Service Parameters - PLOGI
- Discard error policy only. Simple and clean, slay 🧼
8. Security Considerations 🔐
8.1 IP and ARP Related
IP and ARP do not introduce any new security concerns beyond what already exists within the Fibre Channel Protocols and Technology. Therefore IP and ARP related Security does not require special consideration in this document. Honestly a relief, but don't get too comfy 🙈
8.2 FC Related
FC Standards [11] specify a Security Key Server (independent of IP and ARP) as an optional service. However, there are no known implementations of this server yet. Also, the previously defined [2] use of a Security Header has been discontinued [11]. Okay so the key server is a maybe, nobody's built it yet, and the Security Header is retired. Serious stuff, bestie 💀
9. Acknowledgement 🫶
This specification is based on FCA IP Profile, Version 3.3. The FCA IP Profile was a joint work of the Fibre Channel Association (FCA) vendor community. The following organizations or individuals have contributed to the creation of the FCA IP Profile: Adaptec, Ancor, Brocade, Clariion, Crossroads, emf Associates, Emulex, Finisar, Gadzoox, Hewlett Packard, Interphase, Jaycor, McData, Migration Associates, Orca Systems, Prisa, Q-Logic, Symbios, Systran, Tektronix, Univ. of Minnesota, Univ. of New Hamshire. Jon Infante from Emulex deserves special mention for his contributions to the FARP Protocol. The authors extend their thanks to all who provided comments and especially to Lansing Sloan from LLNL for his detailed comments. So many legends in one list, I'm screaming 🌟
10. References 📚
- [1] FCA IP Profile, Revision 3.3, May 15, 1997
- [2] Fibre Channel Physical and Signaling Interface (FC-PH) , ANSI X3.230-1994
- [3] Fibre Channel Link Encapsulation (FC-LE), Revision 1.1, June 26, 1996
- [4] Fibre Channel Fabric Loop Attachment (FC-FLA), Rev. 2.7, August 12, 1997
- [5] Fibre Channel Private Loop SCSI Direct Attach (FC-PLDA), Rev. 2.1, September 22, 1997
- [6] Fibre Channel Physical and Signaling Interface-2 (FC-PH-2), Rev. 7.4, ANSI X3.297-1996
- [7] Fibre Channel Arbitrated Loop (FC-AL), ANSI X3.272-1996
- [8] Postel, J. and J. Reynolds, "A standard for the Transmission of IP Datagrams over IEEE 802 Networks", STD 43, RFC 1042, February 1988.
- [9] Plummer, D. "An Ethernet Address Resolution Protocol -or- Converting Network Addresses to 48-bit Ethernet Address for Transmission on Ethernet Hardware", STD 37, RFC 826, November 1982.
- [10] FCSI IP Profile, FCSI-202, Revision 2.1, September 8, 1995
- [11] Fibre Channel Physical and Signaling Interface -3 (FC-PH-3), Rev. 9.3, ANSI X3.303-199x
- [12] Fibre Channel-The Basics, "Gary R. Stephens and Jan V. Dedek", Ancot Corporation
- [13] Fibre Channel -Gigabit Communications and I/O for Computers Networks "Alan Benner", McGraw-Hill, 1996, ISBN 0-07-005669-2
- [14] Fibre Channel Generic Services -2 (FC-GS-2), Rev. 5.2 X3.288-199x
- [15] Bradley, T. and C. Brown, "Inverse Address Resolution Protocol", RFC 1293, January 1992.
- [16] Bradley, T., Brown, C. and A. Malis, "Inverse Address Resolution Protocol", RFC 2390, August 1992.
- [17] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
- [18] The Fibre Channel Consultant: A Comprehensive Introduction, "Robert W. Kembel", Northwest Learning Associates, 1998
- [19] Bradner, S., "Key Words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
- [20] Narten, T. and C. Burton, "A Caution on The Canonical Ordering of Link-Layer Addresses", RFC 2469, December 1998.
11. Authors' Addresses 💌
Murali Rajagopal Gadzoox Networks, Inc. 711 Kimberly Avenue, Suite 100 Placentia, CA 92870
Phone: +1 714 577 6805 Fax: +1 714 524 8508 EMail: murali@gadzoox.com
Raj Bhagwat Gadzoox Networks, Inc. 711 Kimberly Avenue, Suite 100 Placentia, CA 92870
Phone: +1 714 577 6806 Fax: +1 714 524 8508 EMail: raj@gadzoox.com
Wayne Rickard Gadzoox Networks, Inc. 711 Kimberly Avenue, Suite 100 Placentia, CA 92870
Phone: +1 714 577 6803 Fax: +1 714 524 8508 EMail: wayne@gadzoox.com
Appendix A: Additional Matching Mechanisms in FARP 💖
Okay so, Section 5 already covered how the FC Layer maps the WW_PN to the Port_ID using FARP 🎀 This appendix is about the other optional criteria for address matching, which are:
- WW_NN
- WW_PN & WW_NN at the same time
- IPv4
- IPv4 & WW_PN at the same time
- IPv4 & WW_NN at the same time
- IPv4 & WW_PN & WW_NN at the same time
Depending on the Match Address Code Points, FARP basically resolves three main types of addresses to Port_IDs, and the table below breaks it down 💅
- Match Address Code Point
b'001': the WW_PN Names fields are used to resolve the WW_PN names to Port_IDs. The WW_NN and IP address fields aren't used with these Code Points, so they SHALL be set to either'0'or valid addresses by Requester or Requester and Responder. - Match Address Code Point
b'010': the WW_NN Names fields are used to resolve the WW_NN names to Port_IDs. The WW_PN and IP address fields aren't used with these Code Points, so they SHALL be set to either'0'or valid addresses by Requester or Requester and Responder. - Match Address Code Point
b'100': the IPv4 fields are used to resolve the IPv4 addresses to Port_IDs. The WW_PN and WW_NN fields aren't used with these Code Points, so they SHALL be set to either'0'or valid addresses by Requester or Requester and Responder. - All other Match Address Code Points
b'011',b'101',b'110',b'111': depending on which bits are set, one or more addresses are jointly resolved to a Port_ID. See the table below. If fields are not used, then they are set either to'0'or valid addresses.
The Responder Flags stay the same as before. Also, there can be utmost one FARP-REPLY per FARP-REQ 🦋
Here are the tables showing the FARP-REQ and FARP-REPLY and how the address fields get set 🌸
+--------------------------------------------------------------------+
| Match Address Code Points |
+--------------------------------------------------------------------+
| LSBits| Bit name | Action |
+-------+--------------------+---------------------------------------+
| 000 | Reserved | |
+-------+--------------------+---------------------------------------+
| 001 | MATCH_WW_PN | If 'WW_PN of Responder' = |
| | | Node's WW_PN then respond |
+-------+--------------------+---------------------------------------+
| 010 | MATCH_WW_NN | If 'WW_NN of Responder' = |
| | | Node's WW_NN then respond |
+-------+--------------------+---------------------------------------+
| 011 | MATCH_WW_PN_NN | If both 'WW_PN of Responder' & |
| | | 'WW_NN of Responder' = |
| | | Node's WW_PN & WW_NN then respond |
+-------+--------------------+---------------------------------------+
| 100 | MATCH_IPv4 | If 'IPv4 Address of Responder' = |
| | | Node's IPv4 Address then respond |
+-------+--------------------+---------------------------------------+
| 101 | MATCH_WW_PN_IPv4 | If 'WW_PN & IPv4 of Responder' = |
| | | Node's WW_PN and IPv4 then respond |
+-------+--------------------+---------------------------------------+
| 110 | MATCH_WW_NN_IPv4 | If both 'WW_NN of Responder' & |
| | | 'IPv4 Address of Responder' = |
| | | Node's WW_NN & IPv4 then respond |
+-------+--------------------+---------------------------------------+
| 111 |MATCH_WW_PN_NN_IPv4 | If 'WW_PN of Responder' & |
| | | 'WW_NN of Responder' & |
| | | 'IPv4 Address of Responder' = |
| | | Nodes' WW_PN & WW_NN & IPv4 |
| | | then respond |
+-------+--------------------+---------------------------------------+
+---------------------------------------------------------------------+
| FARP-REQ Command |
+-------------------------------+---------+---------------------------+
| Field | Size | Remarks |
| | (Bytes) | |
+-------------------------------+---------+---------------------------+
| 0x54-00-00-00 | 4 | Request Command Code |
+-------------------------------+---------+---------------------------+
| Match Address Code Points | 1 | Indicates Address |
| | | Matching Mechanism |
+-------------------------------+---------+---------------------------+
| Port_ID of Requester | 3 |Supplied by Requester |
+-------------------------------+---------+---------------------------+
| Responder Flags | 1 |Response Action to be taken|
+-------------------------------+---------+---------------------------+
| Port_ID of Responder | 3 | Set to 0x00-00-00 |
+-------------------------------+---------+---------------------------+
|WW_PN of Requester | 8 | Supplied by Requester |
+-------------------------------+---------+---------------------------+
|WW_NN of Requester | 8 |OPTIONAL; |
| | |Supplied by Requester |
+-------------------------------+---------+---------------------------+
|WW_PN of Responder | 8 |Supplied by Requester |
+-------------------------------+---------+---------------------------+
|WW_NN of Responder | 8 |OPTIONAL ;Supplied by |
| | |Requester or Responder |
+-------------------------------+---------+---------------------------+
|IP Add. of Requester | 16 |OPTIONAL; Supplied by |
| | |Requester |
| | |IPv4 Add.=low 32 bits |
+-------------------------------+---------+---------------------------+
|IP Address of Responder | 16 |OPTIONAL; Supplied by |
| | |Requester or Responder |
| | |IPv4 Add.=low 32 bits |
+-------------------------------+---------+---------------------------+
+---------------------------------------------------------------------+
| FARP-REPLY Command |
+-------------------------------+---------+---------------------------+
| Field | Size | Remarks |
| | (Bytes) | |
+-------------------------------+---------+---------------------------+
| 0x55-00-00-00 | 4 |Reply Command Code |
+-------------------------------+---------+---------------------------+
| Match Address Code Points | 1 | Not Used and unchanged |
| | |from the FARP-REQ |
+-------------------------------+---------+---------------------------+
| Port_ID of Requester | 3 |Supplied by Requester |
+-------------------------------+---------+---------------------------+
| Responder Flags | 1 | Not Used and unchanged |
| | |from the FARP-REQ |
+-------------------------------+---------+---------------------------+
| Port_ID of Responder | 3 |Supplied by Responder |
+-------------------------------+---------+---------------------------+
|WW_PN of Requester | 8 |Supplied by Requester |
+-------------------------------+---------+---------------------------+
|WW_NN of Requester | 8 |OPTIONAL; Supplied by |
| | |Requester |
+-------------------------------+---------+---------------------------+
|WW_PN of Responder | 8 |Supplied by Requester |
+-------------------------------+---------+---------------------------+
|WW_NN of Responder | 8 |OPTIONAL; Supplied by |
| | |Requester or Responder |
+-------------------------------+---------+---------------------------+
|IP Add. of Requester | 16 |OPTIONAL; Supplied by |
| | |Requester |
| | |IPv4 Add.=low 32 bits |
+-------------------------------+---------+---------------------------+
|IP Address of Responder | 16 |OPTIONAL; Supplied by |
| | |Requester or Responder |
| | |IPv4 Add.=low 32 bits |
+-------------------------------+---------+---------------------------+Appendix B: InARP 🧚
B.1 General Discussion 💜
Inverse ARP (InARP) is a mechanism described in RFC 1293/2390 [15, 16]. It's useful when a node wants to know the protocol address of a target node whose hardware address it already knows. The situations where this could happen are described in [15, 16] ✨
The reason FC cares about InARP is so a node can learn the IP address of another node it has done a Port Login (PLOGI) with. PLOGI is a normal FC process that happens between nodes, totally independent of this standard. PLOGI lets a node discover the WW_PN and the Port_ID of the other node, but not its IP address. So a node can potentially get the IP addresses of all the nodes it can PLOGI with 🌈
Note that using InARP can end up resolving all WW_PN to IP addresses, which means ARP may no longer be required. This is super useful in cases where a particular FC topology makes it inefficient to send out an ARP broadcast 🙈
B.2 InARP Protocol Operation 🎀
InARP uses the same ARP Packet format, just with different 'Op Codes': one for InARP Request and another for InARP Reply 💖
The InARP protocol operation is very simple. The requesting node fills in the hardware address (WW_PN) of the target device and sets the protocol address to 0x00-00-00-00. Because the request goes to a node whose WW_PN and Port_ID are already known, there's no need for a broadcast 🫶 The target node fills in its protocol address (an IP address in this case) and sends an InARP Reply back to the sender. A node can collect all of these WW_PN and IP address pairs in a similar way 🦋
B.3 InARP Packet Format 🎀
Okay so InARP uses the same packet format as ARP, which means a lot of what we already covered in Section 4 applies here too 💅 no need to reinvent the wheel!
InARP is 28-bytes long in this application and comes in two packet types: Request and Reply. Just like ARP, the InARP Packet fields are shared by both InARP Requests and InARP Replies ✨
InARP Request and Reply Packets get encapsulated in a single frame FC Sequence, very similar to ARP. Compliant InARP Request and Reply FC Sequences SHALL include Network_Headers 🦋
Now the field rules, bestie 🫶
- The
'HW Type'field SHALL be set to0x00-01. - The
'Protocol'field SHALL be set to0x08-00, indicating IP protocol. - The
'HW Addr Length'field SHALL be set to0x06, indicating 6-bytes of HW address. - The
'Protocol Addr Length'field SHALL be set to0x04, indicating 4-bytes of IP address. - The
'Operation'Code field SHALL be set as follows:
0x00-08 for InARP Request
0x00-09 for InARP Reply- The
'HW Addr of Sender'field SHALL be the 6-byte IEEE MAC address of the Requester (InARP Request) or Responder (InARP Reply). - The
'Protocol Addr of Sender'field SHALL be the 4-byte IP address of the Requester (InARP Request) or Responder (InARP Reply). - The
'HW Addr of Target'field SHALL be set to the 6-byte MAC address of the Responder in an InARP Request, and to the 6-byte MAC address of the Requester in an InARP Reply. - The
'Protocol Addr of Target'field SHALL be set to0x00-00-00-00in an InARP Request, and to the 4-byte IP address of the Requester in an InARP Reply.
B.4 InARP Support Requirements 🌸
Support for InARP is OPTIONAL 🍓 If a node doesn't support InARP and it receives an InARP Request message, then a silent behavior is specified 🙈
APPENDIX C: Some Informal Mechanisms for FC Layer Mappings 🧚
Each method SHALL have some check to make sure PLOGI has completed successfully before any data gets sent. A related concern in large networks is limiting concurrent logins to only those ports with active IP traffic 💜
C.1 Login on Cached Mapping Information 🌈
This one insulates the level doing Login from the level interpreting ARP. It's more accommodating of non-ARP mechanisms for building the FC-layer mapping table, so it's giving flexibility ✨
- Broadcast messages that carry a Network_Header contain the S_ID on the FC-header and WW_PN in the Network-Header. Caching this information gives you a correlation of Port_ID to WW_PN. If the received Broadcast message is compliant with this specification, the WW_PN will contain the MAC Address.
- The WW_PN is "available" if Login has been performed to the Port_ID and flagged. If Login has not been performed, the WW_PN is "unavailable".
- If an outbound packet is destined for a port that is "unavailable", the cached information (from broadcast) is used to look up the Port_ID.
- After sending an ELS PLOGI command (Port Login) to the Port (from a higher level entity at the host), waiting for an outbound packet before sending this Port Login conserves resources for only those ports which wish to establish communication 🫶
- After Port Login completes (ACC received), the outbound packet can be forwarded. At this point, both ends have the necessary information to complete their
<IP address, MAC Address, Port_ID>association 🎀
C.2 Login on ARP Parsing 💅
This method performs Login sooner, by parsing ARP before passing it up to higher levels for IP/MAC Address correlation. It needs a low-level awareness of the IP address, so it's protocol-specific 🔥
- When an ARP Broadcast Message is received, the S_ID is extracted from the FC-header and the corresponding Network_Source_Address from the Network_Header.
- The ARP payload is parsed to determine if
- (a) this host is the target of the ARP request (Target IP Address match), and
- (b) if this host is currently logged in with the port (Port_ID = S_ID) originating the ARP broadcast.
- The ARP is passed to a higher level for ARP Response generation.
- If a Port Login is required, an ELS PLOGI command (Port Login) is sent immediately to the Port originating the ARP Broadcast.
- After Port Login completes, an ARP response can be forwarded. Note that there are two possible scenarios:
- The ACC to PLOGI returns before the ARP reply is processed, and the ARP Reply is immediately forwarded.
- The ARP reply is delayed, waiting for ACC (successful Login).
- At this point, both ends have the necessary information to complete their
<IP address, MAC Address, Port_ID>association 🦋
C.3 Login to Everyone 👑
In Fibre Channel topologies with a limited number of ports, it may be efficient to unconditionally Login to each port. This method is discouraged in fabric and public loop environments 🙈
After Port Login completes, the MAC Address to Port_ID Address tables can be constructed ✨
C.4 Static Table 🧸
In some loop environments with a limited number of ports, a static mapping from a MAC Address to Port_ID (D_ID or AL_PA) may be maintained. The FC layer will always know the destination Port_ID based on the table. The table is typically downloaded into the driver at configuration time. This method scales poorly, and is therefore not recommended 💀
Appendix D: FC Layer Address Validation 🔐
D.1 General Discussion 💖
At all times, the <WW_PN, Port_ID> mapping MUST be valid before use. Lowkey the most important rule in this whole appendix 😭
There are a bunch of events that can invalidate this mapping. The following discussion covers the conditions where validation is required 🌸
After a FC link interruption occurs, the Port_ID of a port may change. After the interruption, the Port_IDs of all other ports that have previously performed PLOGI (N_Port Login) with this port may have changed, and its own Port_ID may have changed too 🌪️
Because of this, address validation is required after a LIP in a loop topology [7], or after NOS/OLS in a point-to-point topology [6] 🫶
Port_IDs will not change as a result of Link Reset (LR), so address validation is not required 💅
In addition to actively validating devices after a link interruption, if a port receives any FC-4 data frames (other than broadcast frames) from a port that is not currently logged in, then it shall send an explicit Extended Link Service (ELS) Request logout (LOGO) command to that port 🚫
ELS commands (Requests and Replies) are used by an N_Port to solicit a destination port (F_Port or N_Port) to perform some link-level function or service.) The LOGO Request is used to request invalidation of the service parameters and Port_ID of the recipient N_Port 🧚
The level of initialization and the subsequent validation and recovery reported to the upper (FC-4) layers is implementation-specific 🎀
In general, an explicit Logout (LOGO) SHALL be sent whenever the FC-Layer mapping between the Port_ID and WW_PN of a remote port is removed 🔥
The effect of power-up or re-boot on the mapping tables is outside the scope of this specification 🙈
D.2 FC Layer Address Validation in a Point-to-Point Topology 🦋
No validation is required after LR. In a point-to-point topology, NOS/OLS causes implicit Logout of each port, and after a NOS/OLS, each port must perform a PLOGI [2] 🌈
D.3 FC Layer Address Validation in a Private Loop Topology 🌀
After a LIP, a port SHALL not transmit any link data to another port until the address of the other port has been validated. The validation consists of completing either ADISC or PDISC. (See Appendix G.) 🛑
ADISC (Address Discovery) is an ELS command for discovering the hard addresses (the 24-bit identifier) of NL_Ports [5], [6] 🔍
PDISC (Discover Port) is an ELS command for exchanging service parameters without affecting Login state [5], [6] 🤝
As a requester, this specification prohibits PDISC and requires ADISC 🙅♀️
As a responder, an implementation may need to respond to both ADISC and PDISC for compatibility with other FC specifications 💖
If the three addresses, Port_ID, WW_PN, and WW_NN, exactly match the values prior to the LIP, then any active exchanges may continue ✨
If any of the three addresses have changed, then the node must be explicitly Logged out [4], [5] 😬
If a port's N_Port ID changes after a LIP, then all active Port-ID to WW_PN mappings at this port must be explicitly Logged out 💜
D.4 FC Layer Address Validation in a Public Loop Topology 🌊
A FAN (Fabric Address Notification) ELS command is sent by the fabric to all known, previously logged in ports following an initialization event. So after a LIP, hosts may wait for this notification to arrive, or they may perform a FLOGI 📬
If the WW_PN and WW_NN of the fabric FL_Port, contained in the FAN ELS or FLOGI response, exactly match the values before the LIP, and if the AL_PA obtained by the port is the same as the one before the LIP, then the port may resume all exchanges. If not, then FLOGI (Fabric Login) must be performed with the fabric, and all nodes must be explicitly Logged out 🌸
A public loop device will have to perform the private loop authentication to any nodes on the local loop which have an Area + Domain Address == 0x00-00-XX 🫶
D.5 FC Layer Address Validation in a Fabric Topology 🏰
No validation is required after LR (link reset) ✨
After NOS/OLS, a port must perform FLOGI. If, after FLOGI, the S_ID of the port, the WW_PN of the fabric, and the WW_NN of the fabric are the same as before the NOS/OLS, then the port may resume all exchanges. If not, all nodes must be explicitly, Logged out [2] 💅
APPENDIX E: Fibre Channel Overview 🧚♀️
E.1. Brief Tutorial 🎀
okay so the FC Standard [2] defines 5 "levels" (not layers, bestie, this matters 💅) for its protocol description: FC-0, FC-1, FC-2, FC-3, and FC-4. The first three levels (FC-0, FC-1, FC-2) are mostly about the physical formatting and control stuff 🔧
FC-3 is kind of a placeholder 🧚. It's built for functions that might need to run after an upper layer protocol asks for an information unit to be sent, but before FC-2 is asked to deliver that piece of information as a sequence of frames [18]. Right now, no FC-3 functions have been defined, so it's giving empty room 🫧
FC-4 is for supporting profiles of Upper Layer Protocols (ULP) like IP and Small Computer System Interface (SCSI) 🌸 It supports a relatively small set compared to LAN protocols like IEEE 802.3, so it's a more focused menu 🍓
FC devices are called "Nodes" 👑 Each Node has at least one "Port" to connect to other ports. A Node can be a workstation, a disk drive or disk array, a camera, a display unit, and more. A "Link" is two unidirectional paths flowing in opposite directions, connecting two Ports within adjacent Nodes 🔗
FC Nodes talk to each other using higher layer protocols like SCSI and IP. They can be set up to operate in a Point-to-Point, Private Loop, Public Loop (attached to a Fabric), or Fabric network topology ✨
Point-to-point is the simplest of the four topologies, where only two nodes talk to each other 🦋 A private loop can connect a number of devices (max 126) in a logical ring, kind of like Token Ring 💜 It's different from a public loop because there's no Fabric Node taking part in the loop. The Fabric topology is a switched network, so any attached node can communicate with any other 🌈 For a detailed description of FC topologies, check [18].
The table below sums up how port types are used depending on their location [12]. E-Port isn't relevant to anything in this specification, but it's here for completeness 🙈
+-----------+-------------+-----------------------------------------+
| Port Type | Location | Topology Associated with |
+-----------+-------------+-----------------------------------------+
| N_Port | Node | Point-to-Point or Fabric |
+-----------+-------------+-----------------------------------------+
| NL_Port | Node |In N_Port mode -Point-to-Point or Fabric |
| | |In NL_Port mode - Arbitrated Loop |
+-----------+-------------+-----------------------------------------+
| F_Port | Fabric | Fabric |
+-----------+-------------+-----------------------------------------+
| FL_Port | Fabric | In F_Port mode - Fabric |
| | | In FL_Port mode - Arbitrated Loop |
+-----------+-------------+-----------------------------------------+
| E_Port | Fabric | Internal Fabric Expansion |
+-----------+-------------+-----------------------------------------+E.2. Exchange, Information Unit, Sequence, and Frame 💖
The FC 'Exchange' is a mechanism that two FC ports use to identify and manage an operation between them [18]. An Exchange opens whenever an operation starts between two ports, and it closes when that operation ends 🔐
The FC-4 Level specifies data units for each type of application level payload, called 'Information Unit' (IU) 📦 Each protocol carried by FC has a defined size for its IU. Every operation must have at least one IU. Lower FC levels map this to an FC Sequence 🧩
A Sequence usually has more than one frame. Larger user data gets segmented and reassembled using two methods: Sequence Count and Relative Offset [18]. With Sequence Count, data blocks are sent in frames with increasing sequence counts (modulo 65536), and it's pretty straightforward to detect the first frame that contains the Network_Header 🎯 With Relative Offset, some computation is needed, as frames arrive, to detect that same first frame 🧮 Both the Sequence Count and Relative Offset field control information are carried in the FC Header 🫶
The FC-4 Level makes a request to the FC-3 Level when it wants something delivered 📬 Right now there are no defined FC-3 level functions, so this level just turns the Information Unit delivery request into a 'Sequence' delivery request and passes it on to the FC-2 Level 🌷 That means each FC-4 Information Unit corresponds to one FC-2 Level Sequence ✨
The maximum data carried by an FC frame cannot exceed 2112-bytes [2]. If the Information Unit goes over that, FC-2 breaks it into multiple frames and sends them as a sequence 💅
There can be multiple Sequences within an Exchange. They're processed sequentially, and only one Sequence is active at a time 🚦 Within an Exchange, information may flow in one direction only, or in both. If it's bi-directional, one of the ports has the initiative to send the next Sequence for that Exchange. Sequence Initiative can get passed between the ports on the last frame of a Sequence, when control is transferred. This amounts to half-duplex behavior 🦋
Ports can have more than one Exchange open at a time, and they can multiplex between Exchanges 🌈 Exchanges are uniquely identified by Exchange IDs (X_ID). An Originator OX_ID and a Responder RX_ID together uniquely identify an Exchange 🔑
E.3. Fibre Channel Header Fields 🧚♀️
The FC header, as shown in the diagrams below, carries routing and other control information for managing Frames, Sequences, and Exchanges 📋 The Frame-header is sent as 6 transmission words immediately after an SOF delimiter and before the Data Field 🎀
D_ID and S_ID
FC uses destination address routing [12], [13] 🗺️ Frame routing in a point-to-point topology is trivial 😌
For the Arbitrated Loop topology, when the destination NL_Port is on the same AL, the source port has to pick the destination port, figure out its AL Physical Address, and "Open" the destination port 🔓 The frames pass through other NL_Ports or the FL_Port on the loop between source and destination, but those ports don't capture the frames. They just repeat and transmit the frame along 🔁 Either communicating port can "Close" the circuit 🔒
When the destination port is not on the same AL, the source NL_Port must open the FL_Port attached to a Fabric 🚪 Once in the Fabric, the Fabric routes the frames again until they reach the destination 🛣️
In a Fabric topology, the Fabric looks into the Frame-header, pulls out the destination address (D_ID), searches its own routing tables, and sends the frame to the destination port along the path it chose 🛤️ Choosing a path may happen at each fabric element or switch, until the F_Port attached to the destination N_Port is reached 💜
Fibre Channel Frame Header, Network_Header, and Payload carrying IP
Packet
+---+----------------+----------------+----------------+--------------+
|Wrd| <31:24> | <23:16> | <15:08> | <07:00> |
+---+----------------+----------------+----------------+--------------+
|0 | R_CTL | D_ID |
+---+----------------+----------------+----------------+--------------+
|1 | CS_CTL | S_ID |
+---+----------------+----------------+----------------+--------------+
|2 | TYPE | F_CTL |
+---+----------------+----------------+----------------+--------------+
|3 | SEQ_ID | DF_CTL | SEQ_CNT |
+---+----------------+----------------+----------------+--------------+
|4 | OX_ID | RX_ID |
+---+--------+-------+----------------+----------------+--------------+
|5 | Parameter (Control or Relative Offset for Data ) |
+---+-----------------------------------------------------------------+
|6 | NAA | Network_Dest_Address (Hi order bits) |
+---+--------+-------+----------------+----------------+--------------+
|7 | Network_Dest_Address (Lo order bits) |
+---+--------+-------+----------------+----------------+--------------+
|8 | NAA | Network_Src_Address (Hi order bits) |
+---+--------+-------+----------------+----------------+--------------+
|9 | Network_Src_Address (Lo order bits) |
+---+----------------+----------------+----------------+--------------+
|10 | DSAP | SSAP | CTRL | OUI |
+---+----------------+----------------+----------------+--------------+
|11 | OUI | PID |
+---+----------------+----------------+----------------+--------------+
|12 | IP Packet Data ... |
+---+----------------+----------------+----------------+--------------+R_CTL (Routing Control) and TYPE(data structure) ✨
Okay so frames for each FC-4 can be told apart at the receiving port super easily, thanks to the R_CTL (Routing Control) and TYPE (data structure) fields in the Frame-header. 💖
R_CTL has two sub-fields: Routing bits and Information category. The Routing bits sub-field has specific values that mean FC-4 data follows, and the Information Category tells the receiver the "Type" of data in the frame. The R_CTL and TYPE code points are shown in the diagrams. 🎀
Other Header fields 🦋
F_CTL (Frame Control), SEQ_ID (Sequence Identification), SEQ_CNT (Sequence Count), OX_ID (Originator exchange Identifier), RX_ID (Responder exchange Identifier), and the Parameter fields are all used to manage the contents of a frame and mark information exchange boundaries for the destination port. They're the behind-the-scenes girlies keeping everything organised. 💅
F_CTL(Frame Control) 🌸
The FC_CTL field is a 3-byte field that holds information about the frame content. Most of the other Frame-header fields are for frame identification, but this one is the drama queen. 👑 Among other things, bits in this field indicate the First Sequence, Last Sequence, or End Sequence. The Sequence Initiative bit is used to pass control of the next Sequence in the Exchange over to the recipient. 🫶
SEQ_ID (Sequence Identifier) and SEQ_CNT (Sequence Count) 🧚
This is used to uniquely identify sequences within an Exchange. The <S_ID, D_ID, SEQ_ID> combo uniquely identifies any active Sequence. 🔥 SEQ_CNT uniquely identifies frames within a Sequence, which keeps frame reception in order and lets link control frames get matched up with their related data frames. Iconic. 💜
Originator Exchange Identifier (OX_ID) and Responder Exchange Identifier (RX_ID) 🌈
The OX_ID value ties frames to specific Exchanges that start at a particular N_Port. The RX_ID field does the same job for the Exchange Originator, but from the other side. The OX_ID is meaningful on the Exchange Originator, and the RX_ID is meaningful on the Responder. Two girls, two IDs, one vibe. 🦋
DF_CTL (Data Field Control) 🍓
The DF_CTL field specifies whether optional headers are present or absent between the Frame-header and the Frame Payload. Little but mighty. ✨
PARAMETER 💜
The Parameter field has two meanings, depending on the frame type. For Link Control Frames, it indicates the specific type of Link Control frame. For Data frames, it contains the Relative Offset value, which specifies an offset from an Upper Layer Protocol buffer relative to a base address. Literally two personalities in one field. 🙈
E.4. Code Points for FC Frame 💖
E.4.1. Code Points with IP and ARP Packets 🫧
The code points for FC frames carrying IP and ARP packets are very similar, with one big exception: the PID value in Word 11 is set to 0x08-00 for IP and 0x08-06 for ARP. 🔥 Also, the Network_Header only appears in the first logical frame of an FC Sequence carrying IP. When FC frames carry ARP packets, it's always present, because those are single frame Sequences. Tiny difference, big energy. 💅
Code Points for FC Frame with IP packet Data
+---+----------------+----------------+----------------+------------+
|Wrd| <31:24> | <23:16> | <15:08> | <07:00> |
+---+----------------+----------------+----------------+------------+
| 0 | 0x04 | D_ID |
+---+----------------+----------------+----------------+------------+
| 1 | 0x00 | S_ID |
+---+----------------+----------------+----------------+------------+
| 2 | 0x05 | F_CTL |
+---+----------------+----------------+----------------+------------+
| 3 | SEQ_ID | 0x20 | SEQ_CNT |
+---+----------------+----------------+----------------+------------+
| 4 | OX_ID | RX_ID |
+---+----------------+----------------+----------------+------------+
| 5 | 0xXX-XX-XX-XX Parameter Relative Offset |
+---+------+--------------------------------------------------------+
| 6 | 0001 | 0x000 | Dest. MAC (Hi order bits) |
+---+------+---------+----------------+----------------+------------+
| 7 | Dest. MAC (Lo order bits) |
+---+------+----------+----------------+----------------------------+
| 8 | 0001 | 0x000 | Src. MAC (Hi order bits) |
+---+------+---------+----------------+----------------+------------+
| 9 | Src. MAC (Lo order bits) |
+---+----------------+----------------+----------------+------------+
|10 | 0xAA | 0xAA | 0x03 | 0x00 |
+---+----------------+----------------+----------------+------------+
|11 | 0x00-00 | 0x08-00 |
+---+----------------+----------------+----------------+------------+
|12 | IP Packet Data |
+---+----------------+----------------+----------------+------------+
|13 | ... |
+---+----------------+----------------+----------------+------------+ Code Points for FC Frame with ARP packet Data
+---+----------------+----------------+----------------+------------+
|Wrd| <31:24> | <23:16> | <15:08> | <07:00> |
+---+----------------+----------------+----------------+------------+
| 0 | 0x04 | D_ID |
+---+----------------+----------------+----------------+------------+
| 1 | 0x00 | S_ID |
+---+----------------+----------------+----------------+------------+
| 2 | 0x05 | F_CTL |
+---+----------------+----------------+----------------+------------+
| 3 | SEQ_ID | 0x20 | SEQ_CNT |
+---+----------------+----------------+----------------+------------+
| 4 | OX_ID | RX_ID |
+---+----------------+----------------+----------------+------------+
| 5 | 0xXX-XX-XX-XX Parameter Relative Offset |
+---+------+--------------------------------------------------------+
| 6 | 0001 | 0x000 | Dest. MAC (Hi order bits) |
+---+------+---------+----------------+----------------+------------+
| 7 | Dest. MAC (Lo order bits) |
+---+------+----------+----------------+----------------------------+
| 8 | 0001 | 0x000 | Src. MAC (Hi order bits) |
+---+------+---------+----------------+----------------+------------+
| 9 | Src. MAC (Lo order bits) |
+---+----------------+----------------+----------------+------------+
|10 | 0xAA | 0xAA | 0x03 | 0x00 |
+---+----------------+----------------+----------------+------------+
|11 | 0x00-00 | 0x08-06 |
+---+----------------+----------------+----------------+------------+
|12 | ARP Packet Data |
+---+----------------+----------------+----------------+------------+
|13| ... |
+---+----------------+----------------+----------------+------------+The code points for a FARP-REQ for a specific Match Address Code Point MATCH_WW_PN_NN ( b'011') are shown below. ✨ The important bits here: the IP addresses field of the Requester is set to a valid address, and the responder's is set to '0'. Also keep an eye on the D_ID address and the Port_ID of the Responder. 🧚
The corresponding code point for a FARP-REPLY is also shown below. The thing to watch is the Port_ID of the Responder and the IP address setting of the Responder. 🦋
E.4.2 Code Points with FARP Command
okay so this one is where the FARP frames get their codepoints, and it's giving diagram energy 🦋✨ there are two layouts: one for FARP-REQ (matching on WW_PN and WW_NN) and one for FARP-REPLY. 💅
FARP-REQ layout (MATCH_WW_PN_NN):
Code Points for FC Frame with FARP-REQ Command for MATCH_WW_PN_NN
+---+----------------+----------------+----------------+------------+
|Wrd| <31:24> | <23:16> | <15:08> | <07:00> |
+---+----------------+----------------+----------------+------------+
| 0 | 0x04 | D_ID = |
| | | 0xFF 0xFF 0xFF |
+---+----------------+----------------+----------------+------------+
| 1 | 0x00 | S_ID |
+---+----------------+----------------+----------------+------------+
| 2 | 0x05 | F_CTL |
+---+----------------+----------------+----------------+------------+
| 3 | SEQ_ID | 0x20 | SEQ_CNT |
+---+----------------+----------------+----------------+------------+
| 4 | OX_ID | RX_ID |
+---+----------------+----------------+----------------+------------+
| 5 | 0xXX-XX-XX-XX Parameter Relative Offset |
+---+----------------+----------------+----------------+------------+
| 6 | 0x54 | 0x00 | 0x00 | 0x00 |
+---+----------------+----------------+----------------+------------+
| 7 | Port_ID of Requester = S_ID |Match Addr. |
| | |Code Points |
| | | xxxxx011 |
+---+----------------+----------------+----------------+------------+
| 8 | Port_ID of Responder = |Responder |
| | 0x00 0x00 0x00 |Flags |
+---+----------------+----------------+----------------+------------+
| 9 | 0001 | 0x000 |WW_PN Src. MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|10 | WW_PN Src. MAC (Lo order bits) |
+---+------+----------+---------------+-----------------------------+
|11 | 0001 | 0x000 |WW_NN Src. MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|12 | WW_NN Src. MAC (Lo order bits) |
+---+----------------+----------------+----------------+------------+
|13 | 0001 | 0x000 |WW_PN Src. MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|14 | WW_PN Dest. MAC (Lo order bits) |
+---+------+----------+---------------+-----------------------------+
|15 | 0001 | 0x000 |WW_NN Dest.MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|16 | WW_NN Dest. MAC (Lo order bits) |
+---+----------------+----------------+----------------+------------+
|17 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|18 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|19 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|20 | set to a valid IPv4 Address by Requester if Available |
+--------------------+----------------+---------+-------------------+
|21 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|22 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|23 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
| | 0x00-00-00-00 |
|24 | set to a valid IPv4 Address of Responder if available |
+--------------------+----------------+---------+-------------------+FARP-REPLY layout:
Code Points for FC Frame with FARP-REPLY Command
+---+----------------+----------------+----------------+------------+
|Wrd| <31:24> | <23:16> | <15:08> | <07:00> |
+---+----------------+----------------+----------------+------------+
| 0 | 0x04 | D_ID |
+---+----------------+----------------+----------------+------------+
| 1 | 0x00 | S_ID |
+---+----------------+----------------+----------------+------------+
| 2 | 0x05 | F_CTL |
+---+----------------+----------------+----------------+------------+
| 3 | SEQ_ID | 0x20 | SEQ_CNT |
+---+----------------+----------------+----------------+------------+
| 4 | OX_ID | RX_ID |
+---+----------------+----------------+----------------+------------+
| 5 | 0xXX-XX-XX-XX Parameter Relative Offset |
+---+----------------+----------------+----------------+------------+
| 6 | 0x55 | 0x00 | 0x00 | 0x00 |
+---+----------------+----------------+----------------+------------+
| 7 | Port_ID of Requester = D_ID | xxxxx011 |
+---+----------------+----------------+----------------+------------+
| 8 | Port_ID of Responder = S_ID |Resp. Flag |
+---+----------------+----------------+----------------+------------+
| 9 | 0001 | 0x000 |WW_PN Src. MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|10 | WW_PN Src. MAC (Lo order bits) |
+---+------+----------+---------------+-----------------------------+
|11 | 0001 | 0x000 |WW_NN Src. MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|12 | WW_NN Src. MAC (Lo order bits) |
+---+----------------+----------------+----------------+------------+
|13 | 0001 | 0x000 |WW_PN Src. MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|14 | WW_PN Dest. MAC (Lo order bits) |
+---+------+----------+---------------+-----------------------------+
|15 | 0001 | 0x000 |WW_NN Dest.MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|16 | WW_NN Dest. MAC (Lo order bits) |
+---+----------------+----------------+----------------+------------+
|17 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|18 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|19 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|20 | set to a valid IPv4 Address by Requester |
+--------------------+----------------+---------+-------------------+
|21 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|22 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|23 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|24 | set to a valid IPv4 Address by Responder |
+--------------------+----------------+---------+-------------------+APPENDIX F: Fibre Channel Protocol Considerations 🌸
F.1 Reliability In Class 3
Problem: okay this is the scary part 😭 Sequence ID reuse in Class 3 can conceivably cause missing frame aliasing, which could lead to delivery of corrupted (incorrectly-assembled) data, and the FC level wouldn't detect it. 💀
Prevention: this spec says you need one of the following methods if Class 3 is used. 🛡️
- Continuously increasing Sequence Count (new Login Bit) - both sides must set. When an N_Port sets the PLOGI login bit for continuously increasing SEQ_CNT, it's guaranteeing that it will transmit all frames within an Exchange using a continuously increasing SEQ_CNT (see description in Section B.1 below). 🎀
- After using all SEQ_IDs (0-255) once, must start a new Exchange. It is recommended that a minimum of 4 Exchanges be used before an OX_ID can be reused. 🦋
- Note: If an implementation is not checking the OX_ID when reassembling Sequences, the problem can still occur. Cycling through some number of SEQ_IDs, then jumping to a new Exchange does not solve the problem. SEQ_IDs must still be unique between two N_Ports, even across Exchanges. 👀
- Use only single-frame Sequences. 🍓
F.2 Continuously Increasing SEQ_CNT
this method lets the recipient check incoming frames, knowing exactly which SEQ_CNT value to expect next 🧚 since SEQ_CNT won't repeat for 65,536 frames, the aliasing problem is way less of a thing. ✨
a Login bit (PLOGI) tells everyone that a device always uses a continuously increasing SEQ_CNT, even across transfers of Sequence Initiative. this bit is necessary for interoperability with some devices, and it has other perks too 💜
in the FC-PH-3 [11], the following is supported:
Word 1, bit 17 - SEQ_CNT (S)
0 = Normal FC-PH rules apply
1 = Continuously increasing SEQ_CNT⚠️ bestie, this part is serious: any N_Port that sets Word 1, Bit 17 = 1 is guaranteeing that it will transmit all frames within an Exchange using a continuously increasing SEQ_CNT. Each Exchange SHALL start with SEQ_CNT = 0 in the first frame, and every frame transmitted after that SHALL increment the previous SEQ_CNT by one, even across transfers of Sequence Initiative. Any frames received from the other N_Port in the Exchange shall have no effect on the transmitted SEQ_CNT. 🔥
APPENDIX G: Acronyms and Glossary of FC Terms ✨
okay so this bit is your quick-reference cheat sheet 📚 it's assumed you already know the FC protocol terms and acronyms from the spec [2], but just in case, here's a little glossary so nobody gets lost 🫶
First Frame: the frame that carries the SOFi field 🎀 it means a logical first, and it might not be the first frame that actually shows up in a sequence, so don't get tricked!
Code Point: the coded bit pattern that goes with control fields in frames or packets 🔢
PDU: Protocol Data Unit 💌
ABTS_LS: Abort Sequence Protocol - Last Sequence 🧹 it's a protocol for aborting an exchange, and it works when the ABTS recipient sets the Last_Sequence bit in the BA_ACC ELS to the ABTS 🙈
ADISC: Discover Address 🔍 it's an ELS for finding the Hard Addresses (the 24 bit NL_Port Identifier) of N_Ports 🌸
D_ID: Destination ID 🎯
ES: End sequence 🏁 this FCTL bit in the FC header tells you the frame is the last frame of the sequence 💅
FAN: Fabric Address Notification 📣 an ELS the fabric sends to all the ports that were already logged in, after an initialization event 🌈
FLOGI: Fabric Login 🔑
LIP: Loop Initialization ♻️ a primitive Sequence a port uses to check whether it's part of a loop, or to recover from certain loop errors 🦋
Link: two unidirectional paths flowing in opposite directions, connecting two Ports within adjacent Nodes 🔗
LOGO: Logout 👋
LR: Link reset 🔄 a primitive sequence a port transmits to start the link reset protocol or to recover from a link timeout ✨
LS: Last Sequence of Exchange 🏆 this FCTL bit in the FC header shows the Sequence is the Last Sequence of the Exchange 💖
Network Address Authority: a 4-bit field in Network_Headers that tells apart the different name registration authorities that can be used to identify the WW_PN and the WW_NN 🪪 NAA=b'0001' means IEEE-48-bit MAC addresses 💜
Node: a collection of one or more Ports, identified by a unique World Wide Node Name (WW_NN) 🏠
NOS: Not Operational 🚫 a primitive Sequence sent to show that the port sending it has spotted a link failure or is offline, and is waiting for OLS to be received 😭
OLS: Off line 📴 a primitive Sequence sent to show that the port sending it is either starting the link initialization protocol, receiving and recognizing NOS, or entering the offline state 🌙
PDISC: Discover Port 🧾 an ELS for swapping Service Parameters without messing with Login state 🫧
Primitive Sequence: an Ordered Set that gets sent over and over, continuously, nonstop 🔁
Private Loop Device: a device that does not try Fabric Login (FLOGI) and usually follows PLDA 🙅♀️ the Area and Domain parts of its NL_Port ID must be 0x0000. These devices can't talk to any port that isn't on their local loop 🥺
Public Loop Device: a device whose Area and Domain parts of the NL_Port ID cannot be 0x0000 🌍 to be FLA compliant, it also must try to open AL_PA 0x00 and try FLOGI 🛫 these devices talk to devices on the local loop AND devices on the other side of a Fabric 👑
Port: the transmitter, receiver and their related logic at either end of a link within a Node 🎀 there can be multiple Ports per Node. Each Port has a unique Port_ID, which is volatile, and a unique World Wide Port Name (WW_PN), which is unchangeable 🔒 in this document, "port" may be used interchangeably with NL_Port or N_Port 🫶
Port_ID: Fibre Channel ports are addressed by unique 24-bit Port_IDs 🔢 in a Fibre Channel frame header, the Port_ID shows up as S_ID (Source ID), which identifies the port that started the frame, and as D_ID, which identifies the destination port 🎯 a given port's Port_ID is volatile (changeable), so it can shift 🌊
PLOGI: Port Login 🪄
SI: Sequence Initiative 🤝
World Wide Port_Name (WW_PN): Fibre Channel requires each Port to have an unchangeable WW_PN 💎 Fibre Channel specifies a Network Address Authority (NAA) to tell apart the various name registration authorities that can be used to identify the WW_PN 🪪 a 4-bit NAA identifier, a 12-bit field set to 0x0, and an IEEE 48-bit MAC address together make this a 64-bit field 🧩
World Wide Node_Name (WW_NN): Fibre Channel identifies each Node with an unchangeable WW_NN 🏷️ in a single port Node, the WW_NN and the WW_PN may be identical 🥰
Full Copyright Statement
okay the legal bit, and yes it stays word for word because it's the real deal 📜⚖️
Copyright (C) The Internet Society (1999). All Rights Reserved.
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Acknowledgement
Funding for the RFC Editor function is currently provided by the Internet Society. 🫶✨
📦 where this page comes from
- ietf: rfc2625 1999-06
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms