RFC 7023

MPLS and Ethernet Operations, Administration, and Maintenance (OAM) Interworking

📅 published October 2013, from ietf

RFC 7023: MPLS and Ethernet Operations, Administration, and Maintenance (OAM) Interworking 🎀

Okay bestie, here's the vibe check on the paperwork 📋✨

  • Authors: D. Mohan, Ed. (Nortel Networks), N. Bitar, Ed. (Verizon), A. Sajassi, Ed. (Cisco), S. Delord (Alcatel-Lucent), P. Niger (France Telecom), and R. Qiu (Juniper) 💖
  • Category: Standards Track 🔥
  • ISSN: 2070-1721
  • Date: October 2013 📅
  • Obsoletes / Updates: the title block doesn't list either one 🙈

Abstract 🦋

This document specifies the mapping of defect states between Ethernet Attachment Circuits (ACs) and associated Ethernet pseudowires (PWs) connected in accordance with the Pseudowire Emulation Edge-to-Edge (PWE3) architecture to realize an end-to-end emulated Ethernet service. It standardizes the behavior of Provider Edges (PEs) with respect to Ethernet PW and AC defects. ✨

Status of This Memo 🌸

This is an Internet Standards Track document. 🔥

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. 📚

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7023. 💅

Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. 🎀

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 🧚

Table of Contents 🗂️

   1. Introduction ....................................................4
      1.1. Specification of Requirements ..............................4
   2. Overview ........................................................4
      2.1. Reference Model and Defect Locations .......................6
      2.2. Abstract Defect States .....................................6
   3. Abbreviations and Terminology ...................................7
      3.1. Abbreviations ..............................................7
      3.2. Terminology ................................................8
   4. PW Status and Defects ...........................................9
      4.1. Use of Native Service (NS) Notification ....................9
      4.2. Use of PW Status Notification for MPLS PSNs ...............10
      4.3. Use of BFD Diagnostic Codes ...............................10
      4.4. PW Defect States Entry and Exit Criteria ..................11
           4.4.1. PW Receive Defect State Entry and Exit .............11
           4.4.2. PW Transmit Defect State Entry and Exit ............11
   5. Ethernet AC Defect States Entry and Exit Criteria ..............12
      5.1. AC Receive Defect State Entry and Exit ....................12
      5.2. AC Transmit Defect State Entry and Exit ...................13
   6. Ethernet AC and PW Defect States Interworking ..................14
      6.1. PW Receive Defect State Entry Procedures ..................14
      6.2. PW Receive Defect State Exit Procedures ...................15
      6.3. PW Transmit Defect State Entry Procedures .................16
      6.4. PW Transmit Defect State Exit Procedures ..................16
      6.5. AC Receive Defect State Entry Procedures ..................16
      6.6. AC Receive Defect State Exit Procedures ...................17
      6.7. AC Transmit Defect State Entry Procedures .................17
      6.8. AC Transmit Defect State Exit Procedures ..................18
   7. Security Considerations ........................................18
   8. Acknowledgments ................................................19
   9. References .....................................................19
      9.1. Normative References ......................................19
      9.2. Informative References ....................................20
   Appendix A. Ethernet Native Service Management ....................21

1. Introduction 💖

RFC 6310 [RFC6310] specifies the mapping and notification of defect states between a pseudowire (PW) and the Attachment Circuit (AC) of the end-to-end emulated service. It standardizes the behavior of Provider Edges (PEs) with respect to PW and AC defects for a number of technologies (e.g., Asynchronous Transfer Mode (ATM) and Frame Relay (FR)) emulated over PWs in MPLS and MPLS/IP Packet Switched Networks (PSNs). However, [RFC6310] does not describe this function for the Ethernet PW service owing to its unique characteristics. 🙈

This document specifies the mapping of defect states between ACs and associated Ethernet PWs connected in accordance with the PWE3 architecture [RFC3985] to realize an end-to-end emulated Ethernet service. This document augments the mapping of defect states between a PW and associated AC of the end-to-end emulated service in [RFC6310]. Similar to [RFC6310], the intent of this document is to standardize the behavior of PEs with respect to failures on Ethernet ACs and PWs, so that there is no ambiguity about the alarms generated and consequent actions undertaken by PEs in response to specific failure conditions. 🔥

1.1. Specification of Requirements 📜

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 [RFC2119]. 🫶

2. Overview 🌟

Okay so there are a bunch of Operations, Administration, and Maintenance (OAM) technologies for Ethernet, and they all do different things. This document covers the following Ethernet OAM mechanisms and their interworking with PW OAM mechanisms: 👑

  • Ethernet Link OAM [802.3]
  • Ethernet Local Management Interface (E-LMI) [MEF16]
  • Ethernet Continuity Check (CC) [CFM] [Y.1731]
  • Ethernet Alarm Indication Signaling (AIS) and Remote Defect Indication (RDI) [Y.1731]

Ethernet Link OAM [802.3] allows some link defect states to be detected and communicated across an Ethernet link. When an Ethernet AC is an Ethernet physical port, there may be some application of Ethernet Link OAM [802.3]. Further, E-LMI [MEF16] also allows for some Ethernet Virtual Circuit (EVC) defect states to be communicated across an Ethernet User Network Interface (UNI) where Ethernet UNI constitutes a single-hop Ethernet link (i.e., without any bridges compliant with IEEE 802.1Q/.1ad in between). 🦋

There may be some application of E-LMI [MEF16] for failure notification across single-hop Ethernet ACs in certain deployments that specifically do not support IEEE Connectivity Fault Management [CFM] and/or ITU-T Y.1731 [Y.1731], simply referred to as CFM and Y.1731, respectively, in this document. Mechanisms based on Y.1731 and CFM are applicable in all types of Ethernet ACs. Ethernet Link OAM and E-LMI are optional, and their applicability is called out, where applicable. 💜

Native service (NS) OAM may be transported transparently over the corresponding PW as user data. This is referred to as the "single emulated OAM loop mode" per [RFC6310]. For Ethernet, as an example, CFM continuity check messages (CCMs) between two Maintenance Entity Group End Points (MEPs) can be transported transparently as user data over the corresponding PW. At MEP locations, service failure is detected when CCMs are not received over an interval that is 3.5 times the local CCM transmission interval. This is one of the failure conditions detected via continuity check. 🌈

MEP peers can exist between customer edge (CE) endpoints (MEPs of a given Maintenance Entity Group (MEG) reside on the CEs), between PE pairs (the MEPs of a given MEG reside on the PEs), or between the CE and PE (the MEPs of a given MEG reside on the PE and CE), as long as the MEG level nesting rules are maintained. It should be noted that Ethernet allows the definition of up to 8 MEG levels, each comprised of MEPs (Down MEPs and Up MEPs) and Maintenance Entity Group Intermediate Points (MIPs). These levels can be nested or touching. MEPs and MIPs generate and process messages in the same MEG level. Thus, in this document, when we refer to messages sent by a MEP or a MIP to a peer MEP or MIP, these MEPs and MIPs are in the same MEG level. 🧚

Main character energy: the MEG level nesting rules are the vibe check for all of this. Keep them intact. 💅

When interworking two networking domains, such as native Ethernet and PWs to provide an end-to-end emulated service, there is a need to identify the failure domain and location even when a PE supports both the NS OAM mechanisms and the PW OAM mechanisms. In addition, scalability constraints may not allow running proactive monitoring, such as CCMs with transmission enabled, at a PE to detect the failure of an EVC across the PW domain. Thus, network-driven alarms generated upon failure detection in the NS or PW domain and their mappings to the other domain are needed. There are also cases where a PE MAY not be able to process NS OAM messages received on the PW even when such messages are defined, as in the case of Ethernet, necessitating the need for fault notification message mapping between the PW domain and the NS domain. 😭

For Multi-Segment PWs (MS-PWs) [RFC5659], Switching PEs (S-PEs) are not aware of the NS. Thus, failure detection and notification at S-PEs will be based on PW OAM mechanisms. Mapping between PW OAM and NS OAM will be required at the Terminating PEs (T-PEs) to propagate the failure notification to the EVC end points. 🫶

2.1. Reference Model and Defect Locations 🗺️

Figure 1 was used in [RFC6310]; it is reproduced in this document as a reference to highlight defect locations. 🦋

                 ACs             PSN tunnel               ACs
                        +----+                  +----+
        +----+          | PE1|==================| PE2|          +----+
        |    |---(a)---(b)..(c)......PW1..(d)..(e)..(f)---(g)---|    |
        | CE1|   (N1)   |    |                  |    |    (N2)  |CE2 |
        |    |----------|............PW2.............|----------|    |
        +----+          |    |==================|    |          +----+
             ^          +----+                  +----+          ^
             |      Provider Edge 1         Provider Edge 2     |
             |                                                  |
             |<-------------- Emulated Service ---------------->|

        Customer                                              Customer
        Edge 1                                                Edge 2

                  Figure 1: PWE3 Network Defect Locations

Part 2 picks up right after Figure 1, with Section 2.2 💖

2.2. Abstract Defect States ✨

Okay so bestie, abstract defect states are also introduced in [RFC6310] 🦋 and this document uses the same conventions as [RFC6310], as you can see in Figure 2 💅. Quick note though: the CE devices in Figure 2 do not necessarily have to be end customer devices 🙈. They're basically devices in client network segments that connect to the Packet Switched Network (PSN) for the emulated services 🌸.

                                   +-----+
              ----AC receive ----->|     |-----PW transmit---->
          CE1                      | PE1 |                    PE2/CE2
              <---AC transmit------|     |<----PW receive-----
                                   +-----+
     (arrows indicate direction of user traffic impacted by a defect)

      Figure 2: Transmit and Receive Defect States and Notifications

The procedures in this document define the entry and exit criteria for each of the four defect states with respect to Ethernet ACs and corresponding PWs 💖. This document also defines the consequent actions that PE1 MUST support to properly interwork these defect states and corresponding notification messages between the PW domain and the native service (NS) domain 🔥. Receive defect state SHOULD have precedence over transmit defect state in terms of handling, when both transmit and receive defect states are identified simultaneously ✨.

Here's the summary from PE1's point of view in Figure 2, no cap 👑:

  • A PW receive defect at PE1 impacts PE1's ability to receive traffic on the PW 😭. Entry and exit criteria for the PW receive defect state are in Section 4.4.1 🫶.
  • A PW transmit defect at PE1 impacts PE1's ability to send user traffic toward CE2 💀. PE1 MAY be notified of a PW transmit defect via a Reverse Defect Indication from PE2, which could point to problems with PE2's inability to receive traffic on the PW or PE2's inability to transmit traffic on its local AC 🧚. Entry and exit criteria for the PW transmit defect state are in Section 4.4.2 🎀.
  • An AC receive defect at PE1 impacts PE1's ability to receive user traffic from the client domain attached to PE1 via that AC 🌈. Entry and exit criteria for the AC receive defect state are in Section 5.1 💜.
  • An AC transmit defect at PE1 impacts PE1's ability to send user traffic on the local AC 🍓. Entry and exit criteria for the AC transmit defect state are in Section 5.2 ⭐.

3. Abbreviations and Terminology 🎀

3.1. Abbreviations 💅

AC    Attachment Circuit
AIS   Alarm Indication Signal
BFD   Bidirectional Forwarding Detection
CC    Continuity Check
CCM   Continuity Check Message
CE    Customer Edge
CV    Connectivity Verification
E-LMI Ethernet Local Management Interface
EVC   Ethernet Virtual Circuit
LDP   Label Distribution Protocol
LoS   Loss of Signal
MA    Maintenance Association
MD    Maintenance Domain
ME    Maintenance Entity
MEG   Maintenance Entity Group
MEP   MEG End Point
MIP   MEG Intermediate Point
MPLS  Multiprotocol Label Switching
MS-PW Multi-Segment Pseudowire
NS    Native Service
OAM   Operations, Administration, and Maintenance
PE    Provider Edge
PSN   Packet Switched Network
PW    Pseudowire
RDI   Remote Defect Indication when used in the context of CCM
RDI   Reverse Defect Indication when used to semantically refer to
      defect indication in the reverse direction
S-PE  Switching Provider Edge
T-PE  Terminating Provider Edge
TLV   Type-Length Value
VCCV  Virtual Circuit Connectivity Verification

3.2. Terminology 🦋

This document uses the following terms with corresponding definitions, bestie 🫶:

  • MEG Level: identifies a value in the range of 0-7 associated with an Ethernet OAM frame 🌸. MEG level identifies the span of the Ethernet OAM frame ✨.
  • MEG End Point (MEP): is responsible for origination and termination of OAM frames for a given MEG 💖.
  • MEG Intermediate Point (MIP): is located between peer MEPs and can process OAM frames but does not initiate them 🧚.
  • MPLS PSN: a PSN that makes use of MPLS Label-Switched Paths [RFC3031] as the tunneling technology to forward PW packets 🌈.
  • MPLS/IP PSN: a PSN that makes use of MPLS-in-IP tunneling [RFC4023] to tunnel MPLS-labeled PW packets over IP tunnels 🔥.

Further, this document also uses the terminology and conventions used in [RFC6310] 💜.

4. PW Status and Defects 🌸

[RFC6310] introduces a range of defects that impact PW status 👑. All these defect conditions are applicable for Ethernet PWs 💅.

Similarly, there are different mechanisms described in [RFC6310] to detect PW defects, depending on the PSN type (e.g., MPLS PSN or MPLS/IP PSN) 🦋. Any of these mechanisms can be used when monitoring the state of Ethernet PWs ✨. [RFC6310] also discusses the applicability of these failure detection mechanisms 🫶.

4.1. Use of Native Service (NS) Notification 💖

When two PEs terminate an Ethernet PW with associated MEPs, each PE can use native service (NS) OAM capabilities for failure notifications by transmitting appropriate NS OAM messages over the corresponding PW to the remote PE 🧚. Options include:

  • Sending of AIS frames from the local MEP to the MEP on the remote PE when the MEP needs to convey PE receive defects and when CCM transmission is disabled 🎀.
  • Suspending transmission of CCM frames from the local MEP to the peer MEP on the remote PE to convey PE receive defects when CCM transmission is enabled 🌈.
  • Setting the RDI bit in transmitted CCM frames when loss of CCMs from the peer MEP is detected or when the PE needs to convey PW reverse defects 🔥.

Similarly, when the defect conditions are cleared, a PE can take one of the following actions, depending on the mechanism that was used for failure notification, to clear the defect state on the peer PE 💜:

  • Stopping AIS frame transmission from the local MEP to the MEP on the remote PE to clear PW receive defects 🍓.
  • Resuming transmission of CCM frames from the local MEP to the peer MEP on the remote PE to clear PW forward defect notification when CCM transmission is enabled ⭐.
  • Clearing the RDI bit in transmitted CCM frames to clear PW transmit defect notification when CCM transmission is enabled 👑.

4.2. Use of PW Status Notification for MPLS PSNs 😭

RFC 4447 [RFC4447] specifies that for PWs that have been set up using the Label Distribution Protocol (LDP), the default mechanism to signal status and defects for ACs and PWs is the LDP status notification message 💅. For PWs established over an MPLS or MPLS/IP PSN using other mechanisms (e.g., static configuration), in-band signaling using VCCV-BFD [RFC5885] SHOULD be used to convey AC and PW status and defects 🫶. Alternatively, the mechanisms defined in [RFC6478] MAY be used 💀.

[RFC6310] identifies the following PW defect status code points 🧚:

  • Forward defect: corresponds to a logical OR of Local Attachment Circuit (ingress) Receive Fault, Local PSN-facing PW (egress) Transmit Fault, and Pseudowire Not Forwarding fault 🎀.
  • Reverse defect: corresponds to a logical OR of Local Attachment Circuit (egress) Transmit Fault and Local PSN-facing PW (ingress) Receive Fault 🌈.

There are also scenarios where a PE carries out PW label withdrawal instead of PW status notification 🔥. These include administrative disablement of the PW or loss of the Target LDP session with the peer PE 💜.

4.3. Use of BFD Diagnostic Codes 🍓

When using VCCV, the control channel type and Connectivity Verification (CV) type are agreed on between the peer PEs using the VCCV parameter field signaled as a sub-TLV of the interface parameters TLV when using FEC 129 and the interface parameter sub-TLV when using FEC 128 [RFC5085] ⭐.

As defined in [RFC6310], when a CV type of 0x04 or 0x10 is used to indicate that BFD is used for PW fault detection only, PW defect is detected via the BFD session while other defects, such as AC defect or PE internal defects preventing it from forwarding traffic, are communicated via an LDP status notification message in MPLS and MPLS/IP PSNs or other mechanisms in L2TP/IP PSNs 👑.

Similarly, when a CV type of 0x08 or 0x20 is used to indicate that BFD is used for both PW fault detection and AC/PW fault notification, all defects are signaled via BFD 😭.

4.4. PW Defect States Entry and Exit Criteria 💅

4.4.1. PW Receive Defect State Entry and Exit 🫶

As described in Section 6.2.1 of [RFC6310], PE1 will enter the PW receive defect state if one or more of the following occur 💀:

  • It receives a Forward Defect Indication (FDI) from PE2 either indicating a receive defect on the remote AC or indicating that PE2 detected or was notified of a downstream PW fault 🧚.
  • It detects loss of connectivity on the PSN tunnel upstream of PE1, which affects the traffic it receives from PE2 🎀.
  • It detects a loss of PW connectivity through VCCV-BFD, VCCV-Ping, or NS OAM mechanisms (i.e., CC) when enabled, which affects the traffic it receives from PE2 🌈.

Note that if the PW LDP control session between the PEs fails, the PW is torn down and needs to be re-established 🔥. However, the consequent actions towards the ACs are the same as if the PW entered the receive defect state 💜.

PE1 will exit the PW receive defect state when the following conditions are met 🍓. Note that this may result in a transition to the PW operational state or the PW transmit defect state ⭐.

  • All previously detected defects have disappeared 👑.
  • PE2 cleared the FDI, if applicable 😭.

4.4.2. PW Transmit Defect State Entry and Exit 💅

PE1 will enter the PW transmit defect state if the following conditions occur 🫶:

  • It receives a Reverse Defect Indication (RDI) from PE2 either indicating a transmit fault on the remote AC or indicating that PE2 detected or was notified of an upstream PW fault 💀.
  • It is not already in the PW receive defect state 🧚.

PE1 will exit the transmit defect state if it receives an OAM message from PE2 clearing the RDI or if it has entered the PW receive defect state 🎀.

5. Ethernet AC Defect States Entry and Exit Criteria 🌈

5.1. AC Receive Defect State Entry and Exit 💖

okay so PE1 enters the AC receive defect state if ANY of these happen 🚨

  • it detects or gets told about a physical-layer fault on the Ethernet interface. Link failure can show up as loss of signal (LoS), or as Ethernet Link OAM [802.3] critical link event notifications from an upstream node CE1 with a "Dying Gasp" or "Critical Event" indication, or as a client Signal Fail message [Y.1731]
  • a MEP tied to the local AC gets an Ethernet AIS frame from CE1
  • a MEP tied to the local AC doesn't hear CCM frames from its peer MEP in the client domain (like CE1) within 3.5 times the CCM transmission period configured for that MEP. this only applies when CCM transmission is enabled
  • a CCM shows up with an Interface Status TLV saying the interface is down. other CCM Interface Status TLV values are NOT used to flag failure or recovery 🙅‍♀️

ngl this next part is my fave 🤓 when a MEP at a PE or a CE gets a CCM with the wrong MEG ID, MEP ID, or MEP level, the receiving PE or CE SHOULD treat that as an AC receive defect. and if those wrong CCMs keep coming for 3.5 times the local MEP CCM transmission time, loss of continuity gets declared at the receiving end. literally a whole vibe check 💀

PE1 exits the AC receive defect state only when ALL the conditions that got it in there are cleared. that means all of these:

  • any physical-layer fault on the Ethernet interface is gone. that covers faults PE1 detected itself or was notified about earlier, so LoS is cleared, or the Ethernet Link OAM [802.3] critical link event notifications with "Dying Gasp" or "Critical Event" are cleared at upstream node CE1
  • the local-AC MEP stops getting Ethernet AIS frames for a period set by the AIS it received earlier, IF that AIS is what got PE1 into the defect state
  • the local-AC MEP (with CCM enabled) gets a configured number (like 3 or more) of consecutive CCM frames from the peer MEP on CE1, all within a multiple (3.5) of the CCM transmission period configured for the MEP 🎀
  • CCM says the interface status is up 🌸

5.2. AC Transmit Defect State Entry and Exit ✨

PE1 enters the AC transmit defect state if either of these is true:

  • it detects or gets notified of a physical-layer fault on the Ethernet interface where the AC is configured (for example, through loss of signal (LoS), or Ethernet Link OAM [802.3] critical link event notifications from an upstream node CE1 with a "Link Fault" indication)
  • a MEP configured with CCM transmission enabled and tied to the local AC gets a CCM frame from the peer MEP in the client domain (like CE1) with its RDI (Remote Defect Indication) bit set 🦋

PE1 exits the AC transmit defect state when ALL the conditions that put it there are cleared. that includes both of these:

  • any physical-layer fault on the Ethernet interface is gone, whether PE1 detected it or was told about it before. so LoS is cleared, or the Ethernet Link OAM [802.3] critical link event notifications with a "Link Fault" indication are cleared at upstream node CE1
  • a MEP configured with CCM transmission enabled and tied to the local AC stops getting CCM frames with the RDI bit set, after it had previously received a CCM frame with the RDI bit set from the peer MEP in the client domain (like CE1) 🫶

6. Ethernet AC and PW Defect States Interworking ✨

6.1. PW Receive Defect State Entry Procedures 🧚

okay this is where it gets juicy 👑 when the PW status on PE1 goes from working to the PW receive defect state, PE1's ability to receive user traffic from CE2 takes a hit. so PE1 has to tell CE1 about the problem 💅

when PE1 enters the PW receive defect state, the following MUST be done:

  • if PE1 has a Down MEP tied to the local AC and CCM transmission is NOT enabled, the MEP tied to the AC MUST transmit AIS frames to the peer MEP in the client domain (like on CE1) on the configured AIS transmission period 🚨
  • if PE1 has a Down MEP tied to the local AC, CCM transmission is enabled, and that MEP is set up to support the Interface Status TLV in CCMs, the MEP tied to the AC MUST transmit CCM frames with the Interface Status TLV marked as Down to the peer MEP in the client domain (like on CE1) 🌈
  • if PE1 has a Down MEP tied to the local AC, CCM transmission is enabled, and that MEP is set up to NOT support the Interface Status TLV in CCMs, the MEP tied to the AC MUST stop transmitting CCM frames to the peer MEP in the client domain (like on CE1) 🙈
  • if PE1 is set up to run E-LMI [MEF16] with CE1 and E-LMI is used for failure notification, PE1 MUST transmit an E-LMI asynchronous STATUS message with report type Single EVC Asynchronous Status saying the PW is Not Active 💜

and then there's this bit 😭 when PE1 enters the receive defect state, it MUST assume PE2 has no idea about the defect, and it MUST send a reverse defect failure notification to PE2. for an MPLS PSN or MPLS/IP PSN, that happens either through a PW status notification message showing a reverse defect, or through a VCCV-BFD diagnostic code of reverse defect, as long as a VCCV CV type of 0x08 or 0x20 was negotiated. and if PE1 supports a native service OAM mechanism, it can also use the NS OAM notification from Section 4.1 🍓

if the PW receive defect state was entered because of a forward defect notification from PE2, or because the control adjacency was lost, no extra action is needed. PE2 is already expected to know about the defect 🦋

6.2. PW Receive Defect State Exit Procedures 🌸

when the PW status goes from the PW receive defect state back to working, PE1's ability to receive user traffic from CE2 comes back. so PE1 needs to stop the defect notifications to CE1, by doing the following:

  • if PE1 has a Down MEP tied to the local AC and CCM transmission is NOT enabled, the MEP tied to the AC MUST stop transmitting AIS frames towards the peer MEP in the client domain (like on CE1) ✨
  • if PE1 has a Down MEP tied to the local AC, CCM transmission is enabled, and that MEP is set up to support the Interface Status TLV in CCMs, the MEP tied to the AC MUST transmit CCM frames with the Interface Status TLV marked as Up to the peer MEP in the client domain (like on CE1) 🎀
  • if PE1 has a Down MEP tied to the local AC, CCM transmission is enabled, and that MEP is set up to NOT support the Interface Status TLV in CCMs, the MEP tied to the AC MUST resume transmitting CCM frames to the peer MEP in the client domain (like on CE1) 💖
  • if PE1 is set up to run E-LMI [MEF16] with CE1 and E-LMI is used for fault notification, PE1 MUST transmit an E-LMI asynchronous STATUS message with report type Single EVC Asynchronous Status saying the PW is Active 👑

also, if PE1 explicitly detected the PW receive defect itself, it MUST now tell PE2 that the receive defect is cleared, by clearing the reverse defect notification. for a PW over an MPLS PSN or MPLS/IP PSN, that's either a PW status message showing a working state, or a VCCV-BFD diagnostic code, as long as a VCCV CV type of 0x08 or 0x20 was negotiated. and if a native service OAM mechanism is supported on PE, it can also clear the NS OAM notification from Section 4.1 🌈

if the PW receive defect was set up through a notification from PE2, or through a lost control adjacency, no extra action is needed. PE2 is already expected to know the defect has cleared 🫶

6.3. PW Transmit Defect State Entry Procedures 🔥

when the PW status goes from working to the PW transmit defect state, PE1's ability to send user traffic to CE2 gets impacted. so PE1 has to let CE1 know about the problem 🚨

when PE1 enters the PW transmit defect state, the following MUST be done:

  • if PE1 has a Down MEP tied to the local AC and CCM transmission is enabled, the MEP tied to the AC MUST set the RDI bit in transmitted CCM frames OR send a status TLV with interface down to the peer MEP in the client domain (like on CE1) 💜
  • if PE1 is set up to run E-LMI [MEF16] with CE1 and E-LMI is used for fault notification, PE1 MUST transmit an E-LMI asynchronous STATUS message with report type Single EVC Asynchronous Status saying the PW is Not Active 🦋
  • if PE1 detected the PW failure WITHOUT getting a reverse defect notification from PE2, PE1 MUST assume PE2 has no idea about the defect, and it MUST notify PE2 by sending an FDI 🙈

6.4. PW Transmit Defect State Exit Procedures 🧚‍♀️

when the PW status goes from the PW transmit defect state back to working, PE1's ability to send user traffic to CE2 is restored. so PE1 needs to stop the defect notifications to CE1 and do the following:

  • if PE1 has a Down MEP tied to the local AC and CCM transmission is enabled, the MEP tied to the AC MUST clear the RDI bit in the transmitted CCM frames to the peer MEP, OR send a status TLV with interface up to the peer MEP in the client domain (like on CE1) 🌸
  • if PE1 is set up to run E-LMI [MEF16] with CE1, PE1 MUST transmit an E-LMI asynchronous STATUS message with report type Single EVC Asynchronous Status saying the PW is Active ✨
  • PE1 MUST clear the FDI to PE2, if that applies 🎀

6.5. AC Receive Defect State Entry Procedures 👑

when the AC status goes from working to the AC receive defect state, PE1's ability to receive user traffic from CE1 gets impacted. so PE1 has to tell both PE2 and CE1 about the problem 😭

if PE1 detects the AC receive defect, it MUST notify PE2 using a forward defect notification 💖

when NS OAM is NOT supported on PE1, for a PW over an MPLS PSN or MPLS/IP PSN, the forward defect notification happens either through a PW status message showing a forward defect, or through a VCCV-BFD diagnostic code of forward defect, as long as a VCCV CV type of 0x08 or 0x20 was negotiated 🌈

if a native service OAM mechanism is supported on PE1, it can also use the NS OAM notification from Section 4.1 🦋

on top of all that, PE1 MUST perform the following:

  • if PE1 has a Down MEP tied to the local AC and CCM transmission is enabled, the MEP tied to the AC MUST set the RDI bit in transmitted CCM frames 🫶

6.6. AC Receive Defect State Exit Procedures ✨

okay so when the AC status goes from AC receive defect state back to working, PE1 can receive user traffic from CE1 again 🥹💖 that means PE1 has to stop sending defect notifications to PE2 and CE1, and it does that in a few ways:

  • When NS OAM isn't supported on PE1, over a PW over MPLS PSN or MPLS/IP PSN, the forward defect notification gets cleared with a PW status message showing a working state, or with a VCCV-BFD diagnostic code if a VCCV CV type of 0x08 or 0x20 was negotiated 🦋
  • When a native service OAM mechanism is supported on PE1, PE1 clears the NS OAM notification as specified in Section 4.1 💅
  • If PE1 is configured with a Down MEP tied to the local AC and CCM transmission is enabled, the MEP associated with the AC MUST clear the RDI bit in transmitted CCM frames to the peer MEP in the client domain (e.g., on CE1). this one is a must-do, bestie 🫶

6.7. AC Transmit Defect State Entry Procedures 🌸

when the AC status goes from working to AC transmit defect state, PE1 can't send user traffic to CE1 anymore 😭 so PE1 has to let PE2 know about the problem, no cap.

if PE1 detects the AC transmit defect, it MUST notify PE2 with a reverse defect notification 🚨

  • When NS OAM isn't supported on PE1, over a PW over MPLS PSN or MPLS/IP PSN, that reverse defect notification is sent either with a PW status message indicating a reverse defect, or with a VCCV-BFD diagnostic code of reverse defect if a VCCV CV type of 0x08 or 0x20 was negotiated 🍓
  • When a native service OAM mechanism is supported on PE1, it can also use the NS OAM notification as specified in Section 4.1 🧚

6.8. AC Transmit Defect State Exit Procedures 💜

when the AC status goes from AC transmit defect state back to working, PE1 can transmit user traffic to CE1 again ✨ so PE1 MUST clear the reverse defect notification to PE2. slay 👑

  • When NS OAM isn't supported on PE1, over a PW over MPLS PSN or MPLS/IP PSN, the reverse defect notification gets cleared with a PW status message showing a working state, or with a VCCV-BFD diagnostic code if a VCCV CV type of 0x08 or 0x20 was negotiated 🎀
  • When a native service OAM mechanism is supported on PE1, PE1 can clear the NS OAM notification as specified in Section 4.1 💖

7. Security Considerations 🔐

okay this part is SO important, so pay attention 🙈 the OAM interworking mechanisms in this document don't change the security functions that already live inside the actual messages. all the generic security considerations for PW traffic in Section 10 of [RFC3985] apply to NS OAM messages carried inside the PW 🛡️

the security considerations in Section 10 of [RFC5085] for VCCV apply to the OAM messages carried this way too. and the security considerations for the PWE3 control protocol, described in Section 8.2 of [RFC4447], apply to OAM indications sent using the LDP status message 💜

here's the big one: because the mechanisms in this document let OAM messages and fault conditions get passed between native service networks and PSNs, the continuity of the end-to-end service depends on a trust relationship between the operators of those networks 😱 for more on that kind of scenario, check Section 7 of [RFC5254] 🥺

8. Acknowledgments 🫶

the authors are so thankful to Samer Salam, Matthew Bocci, Yaakov Stein, David Black, Lizhong Jin, Greg Mirsky, Huub van Helvoort, and Adrian Farrel for their valuable input and comments 💕 iconic group project energy 🌈

9. References 📚

9.1. Normative References

[802.3]    IEEE, "Part 3: Carrier Sense Multiple Access with
           Collision Detection (CSMA/CD) Access Method and Physical
           Layer Specifications (Clause 57 for Operations,
           Administration, and Maintenance)", IEEE Std 802.3-2005,
           December 2005.

[CFM]      IEEE, "Connectivity Fault Management clause of IEEE
           802.1Q", IEEE 802.1Q, 2013.

[MEF16]    Metro Ethernet Forum, "Ethernet Local Management Interface
           (E-LMI)", Technical Specification MEF16, January 2006.

[RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC4447]  Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
           G. Heron, "Pseudowire Setup and Maintenance Using the
           Label Distribution Protocol (LDP)", RFC 4447, April 2006.

[RFC5085]  Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire
           Virtual Circuit Connectivity Verification (VCCV): A
           Control Channel for Pseudowires", RFC 5085, December 2007.

[RFC5885]  Nadeau, T., Ed., and C. Pignataro, Ed., "Bidirectional
           Forwarding Detection (BFD) for the Pseudowire Virtual
           Circuit Connectivity Verification (VCCV)", RFC 5885, June
           2010.

[RFC6310]  Aissaoui, M., Busschbach, P., Martini, L., Morrow, M.,
           Nadeau, T., and Y(J). Stein, "Pseudowire (PW) Operations,
           Administration, and Maintenance (OAM) Message Mapping",
           RFC 6310, July 2011.

[RFC6478]  Martini, L., Swallow, G., Heron, G., and M. Bocci,
           "Pseudowire Status for Static Pseudowires", RFC 6478, May
           2012.

[Y.1731]   ITU-T, "OAM functions and mechanisms for Ethernet based
           networks", ITU-T Y.1731, July 2011.

9.2. Informative References

[RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
           Label Switching Architecture", RFC 3031, January 2001.

[RFC3985]  Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation
           Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.

[RFC4023]  Worster, T., Rekhter, Y., and E. Rosen, Ed.,
           "Encapsulating MPLS in IP or Generic Routing Encapsulation
           (GRE)", RFC 4023, March 2005.

[RFC5254]  Bitar, N., Ed., Bocci, M., Ed., and L. Martini, Ed.,
           "Requirements for Multi-Segment Pseudowire Emulation Edge-
           to-Edge (PWE3)", RFC 5254, October 2008.

[RFC5659]  Bocci, M. and S. Bryant, "An Architecture for Multi-
           Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
           October 2009.

Appendix A. Ethernet Native Service Management 🌷

this appendix is informative 🤍

okay so Ethernet OAM mechanisms fall into two big categories: Fault Management (FM) and Performance Monitoring (PM) 📊 ITU-T Y.1731 [Y.1731] covers both FM and PM, while IEEE CFM [CFM] covers a subset of the FM functions 💅

Ethernet OAM also brings in the idea of a Maintenance Entity (ME), which identifies the entity that needs managing. an ME is inherently point-to-point 🔗 but for multipoint associations you use a Maintenance Entity Group (MEG), made up of different MEs. IEEE 802.1 uses the concept of a Maintenance Association (MA), which covers both point-to-point and multipoint associations ✨ each MEG/MA has MEG End Points (MEPs), which are responsible for originating OAM frames 🧚 and in between the MEPs there can also be MEG Intermediate Points (MIPs). MIPs don't originate OAM frames, but they do respond to OAM frames from MEPs 🦋

Ethernet OAM also allows hierarchical Maintenance Entities, so you can do end-to-end and segment monitoring at the same time 🌈 this works because you can have up to 8 MEG levels (MD levels), and each MEP or MIP is associated with one specific MEG level 👑

it's important to note that the FM mechanisms common to both IEEE CFM [CFM] and ITU-T Y.1731 [Y.1731] are completely compatible 🫶 the common FM mechanisms are:

  1. Continuity Check Message (CCM)
  2. Loopback Message (LBM) and Loopback Reply (LBR)
  3. Link Trace Message (LTM) and Link Trace Reply (LTR)

CCMs are used for fault detection, including misconnections and misconfigurations 🔍 they're typically sent as multicast frames or unicast frames, and they also allow RDI notifications. LBM and LBR are used for fault verification, and they also allow MTU verification and CIR/EIR (Committed Information Rate / Excess Information Rate) measurements 📏 LTM and LTR can be used to discover the path traversed between a MEP and another target MIP/MEP in the same MEG, and they also allow for fault localization 🗺️

on top of that, ITU-T Y.1731 [Y.1731] also specifies this FM function:

  1. Alarm Indication Signal (AIS)

AIS allows fault notification to downstream and upstream nodes 📣

and ITU-T Y.1731 [Y.1731] also specifies these PM functions:

  1. Loss Measurement Message (LMM) and Loss Measurement Reply (LMR)
  2. Delay Measurement Message (DMM) and Delay Measurement Reply (DMR)
  3. 1-way Delay Measurement (1DM)

LMM and LMR are used to measure Frame Loss Ratio (FLR) 📉 DMM and DMR are used to measure single-ended (aka two-way) Frame Delay (FD) and Frame Delay Variation (FDV, also known as Jitter) ⏱️ and 1DM can be used for dual-ended (aka one-way) FD and FDV measurements 💫

Authors' Addresses 💌

Dinesh Mohan (editor)
Nortel Networks
EMail: dinmohan@hotmail.com


Nabil Bitar (editor)
Verizon
60 Sylvan Road
Waltham, MA  02145
United States
EMail: nabil.n.bitar@verizon.com


Ali Sajassi (editor)
Cisco
170 West Tasman Drive
San Jose, CA  95134
United States
EMail: sajassi@cisco.com


Simon Delord
Alcatel-Lucent
215 Spring Street
Melbourne
Australia
EMail: simon.delord@gmail.com


Philippe Niger
France Telecom
2 av. Pierre Marzin
22300 Lannion
France
EMail: philippe.niger@orange.com


Ray Qiu
Juniper
1194 North Mathilda Avenue
Sunnyvale, CA  94089
United States
EMail: rqiu@juniper.net

That's the whole RFC, bestie! 🌈✨ Thanks for sticking with it 🫶💖

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