RFC 1329
Thoughts on Address Resolution for Dual MAC FDDI Networks
Network Working Group 🌸 RFC 1329, titled Thoughts on Address Resolution for Dual MAC FDDI Networks, is by P. Kuehn and dated May 1992. It's Informational, so it provides information for the Internet community and doesn't specify an Internet standard. It doesn't list anything it obsoletes or updates, so it's a clean slate, no drama 🫶
Status of This Memo ✨
This memo provides information for the Internet community. It does not specify an Internet standard. Distribution of this memo is unlimited.
1. Abstract 💖
okay so the big idea here is how IP and ARP can work on inhomogeneous FDDI networks, which are FDDI rings mixing single MAC and dual MAC stations 🦋 The trick is adding a brand-new protocol layer to the stack of the dual MAC stations. Then two dual MAC stations can do load splitting across both rings and use the double bandwidth of 200 Mbits/s, like they're single MAC stations but make it iconic 👑 The new layer is an extension of layer 3. For the user and the higher layer protocols, IP and ARP, the "dual MAC" thing is totally transparent 🙈 No modification is required in the protocol suite of single MAC stations and transparent bridges. Zero changes for them, they don't even have to know 💅
2. Acknowledgements 🎀
This paper is a result of a diploma thesis prepared at the Technical University of Munich, Lehrstuhl fuer Kommunikationsnetze, in co-operation with the Siemens Nixdorf AG. The author would like to thank Jrg Eberspher and Bernhard Edmaier from the university, and Andreas Thimmel and Jens Horstmeier from the SNI AG at Augsburg, for the helpful comments and discussions. Big thanks to the whole crew 🫶🌈
3. Conventions 🧚
These are the terms the rest of the doc keeps coming back to, so bookmark this part 🔖
Primary MAC, P-MAC MAC, placed on the primary ring
Secondary MAC, S-MAC MAC, placed on the secondary ring
Inhomogeneous ring configuration of a dual FDDI ring with
single MAC and dual MAC stations
DMARP Dual MAC Address Resolution Protocol4. Assumptions 🍓
Okay, first the assumptions, because everything else depends on them 🧠 When a dual FDDI ring wraps, both MACs in a dual MAC station are assumed to stay connected to the ring. ANSI is still investigating whether the Configuration Management in the Station Management of an FDDI station can be modified to allow this, so it's not settled yet 👀 According to the FDDI SMT standard [1], different addresses are required for all MACs on the primary and the secondary ring. So every MAC gets its own address, no sharing 💜
In this paper, the MAC in a single MAC station is assumed to reside on the primary ring. Single MAC stations with their MAC on the secondary ring aren't ruled out, but that setup needs additional connectivity between the two rings. Those configurations are beyond the scope of this document, so we're not going there today 🙅♀️
8.4. Timeout of Entries Marked with OR-Bit Set ⏰
Okay bestie, so if a FDDI ring is wrapped 🌀, the DMARP reply frames get picked up by the primary and secondary MACs of the target dual MAC stations. In that case, the entries for dual MAC stations on the same dual ring also get the OR-bit set, even though load sharing is possible between those stations 🙈.
When an OR-bit in an entry gets set for the first time, a timer entity starts. If that timer entity runs out, a DMARP request frame is sent over SNAP 2 to the secondary MAC of the associated target station. Then the entry gets discarded 💀.
If the request can't be received by the target station because the network configuration has changed, there's no entry in the address cache for that station anymore and no load sharing gets computed. If the target station does receive the DMARP request frame, it sends back a DMARP reply frame 🫶.
8.5. Problems with the Application of Large FDDI Networks 🌈
With more and more dual FDDI rings, each one linked together by two transparent bridges, the chance goes up that one of these inhomogeneous dual FDDI rings is wrapped at the exact moment two dual MAC stations swap ARP frames and DMARP replies 😭.
If two dual MAC stations are talking for the first time, the chance goes down that a load sharing actually gets computed after the DMARP replies are exchanged, even though it would be possible according to the network configuration. It depends on DMARP replies reaching the primary ring over the wrapped dual ring, and on only entries with the OR-bit set being created. To fix this, further expedients were invented ✨:
At first, entries in the address cache can be marked read-only by setting the R-bit. In dual MAC stations, entries can be written manually for other dual MAC stations that get talked to a lot or that have a special importance. DMARP can't change the control bits of these entries.
Next, additional control bits are introduced. One of these is the Hold-bit (H-bit) 🎀. When two dual MAC stations exchange ARP frames and DMARP replies to create entries in their address caches, one station starts sending a DMARP reply first. Depending on the network state, it sends an additional DMARP error frame a moment later. Within a maximum period of time (see "Configuring the Timer Parameters"), all frames arrive at the neighbour station and get received by the primary and/or secondary MAC. If the OR-bit wasn't set for an entry within this period, it's clear that no further DMARP frames will be received that would result in setting the OR-bit. For such an entry, the H-bit is set. Since reception of reply and error frames isn't enough to set the OR-bit when the H-bit is set, load sharing is assumed to be sure. The correctness of the H-bit gets verified in relatively long time periods by queries (query and hold frames) at the associated station.
For two communicating stations, there's a possibility to get information from a third station, which is giving main character energy 👑. Whenever the OR-bit is set for an entry in a dual MAC station, a search frame is transmitted by the secondary MAC, containing the station's own primary MAC address and the primary MAC address of the counter station. If a third station can compute a sure load sharing with both stations (the H-bit is set for the associated entries), the stations can perform a load sharing between them, too. The third station informs these stations by sending found frames to them 🦋.
8.6. Multicast and Broadcast Addresses in IP Frames 📣
If the destination hardware address of an IP frame is a multicast or broadcast hardware address, the frame is always delivered to SNAP 1 and sent on the primary ring, because one of the addressed stations could be a single MAC station. IP frames that are delivered to the load sharing entity by SNAP 2 get discarded by the load sharing entity. That way, duplication of these frames can be prevented 💅.
9. Internal Structure 🧚
One load Sharing entity exists in the load sharing layer. This load sharing entity consists of the address cache, the cache administration and the multiplexer 💜.
to ARP to ARP
+----X----------------------------------------------------X--------+
| | | IP |
| | ARP frames read | frames |
| | entries | |
| +----------------------------+ +---------+ +----------+ |
| | Cache Administration |->-| Address |---->--| Multi- | |
| +----------------------------|->-| Cache | | plexer | |
| | | | | +---------+ | | |
| | | | | +----------+ |
| | ARP | DMARP | ARP | DMARP | | |
| | frames | frames | frames | frames IP | IP | |
| | | | | frames | frames | |
| | | | | | | |
+--X--------X--------X--------X-----------------------X--------X---+
to SNAP 1 to SNAP 2 to SNAP 1 to SNAP 29.1. The Address Cache 🗂️
In the address cache, the associations of primary MAC addresses to secondary MAC addresses are stored for other dual MAC stations on the network. There are no entries for single MAC stations 🙅♀️.
Because the OR- and the LS-bit (see table) always have inverted values, one of the bits is redundant. Afterwards, examining an entry state gets easier by introducing both bits, so they're defined together. ARP is able to support other protocol address formats than the IP format. To support this ARP property in DMARP, the protocol type number as used in the ARP frames is stored in every entry of the address cache. So a dual MAC station is able to communicate with another station with DMARP, even if that other station doesn't use IP 🌸. The numbers used in DMARP frames and the address cache for the protocol type and the address length are taken over from ARP.
name length comment
--------------------------------------------------------------------
P-MAC address 48 bit Address of the primary MAC
in an other dual MAC station
S-MAC address 48 bit Address of the secondary MAC
in that station
LS-bit 1 bit A load sharing can be performed
with that station
("Load sharing bit")
OR-bit 1 bit No load sharing may be done
with that station
("Other ring bit")
H-bit 1 bit The load sharing with that
station is trusty.
("Hold bit")
Q-bit 1 bit A query frame was sent to that
station, no hold frame was
received yet ("Query bit")
R-bit 1 bit This entry cannot be changed by
DMARP ("Read-only bit")
V-bit 1 bit The entry is valid
("Valid bit")
subscript 32 bit Unique number, identifying this
entry
protocol type 16 bit Number of the protocol type
that was last used in that
station9.2. The Multiplexer 🔀
The multiplexer deals with multiplexing the IP frames upon the two FDDI rings. Broadcast and multicast frames are always sent on the primary ring. Otherwise, the contents of the address cache and a load sharing criteria are used to decide on which of the rings an IP frame has to be transmitted. If there's no entry for the primary MAC address of the destination station in the cache, the IP frame is transmitted on the primary ring. If there's an entry for the destination station and the LS-bit is set, a load sharing can be done with this station. Later on, a load sharing criteria, which is beyond the scope of this document, decides which one of the rings is used for transmission. An example for a load sharing criteria is the length of the transmit queues in the MACs. The multiplexer only requires an abstract function, which returns the appropriate ring for the transmission of an actual IP frame 🧠.
Additionally, the multiplexer filters the received IP frames: multicast or broadcast frames received from the secondary MAC are discarded 🚫.
9.3. The Cache Administration 🗃️
The cache administration creates and deletes the entries in the address cache. For this purpose, it communicates with other load sharing entities in other dual MAC stations with the DMARP. The cache administration also handles the delivery of ARP frames to the ARP and the SNAP entity in the station, respectively 📬.
The cache administration needs three timers for the communication with the DMARP, which have to be supported by the system environment. Each of these timers must support a timer entity for each entry in the address cache, whereby a single one is running at a time ⏳.
Supported timer services:
TIMER_request(time, name, subscript)
TIMER_response(name, subscript)
TIMER_cancel(name, subscript):A timer entity is started by the service TIMER_request and cancelled by the TIMER_cancel service request. The TIMER_response service indicates that a timer entity has run out. The parameter name is the name of a timer: OR-Entry-Timer, Hold-Timer, or Query-Timer. Each entry in the address cache is uniquely identified by a number subscript). This number is also the number of an associated timer entity. How to dispose these numbers is a question of implementation. The parameter time determines the time period when the timer runs out. This parameter has the value OR-set-timeout for the OR-Entry-Timer, Hold-time for the Hold-Timer and Query-time for the Query-Timer 🌟.
9.4. Configuring the Timer Parameters ⏰
okay bestie, this section is all about setting the three timers so the whole thing actually works 💅 each one has its own vibe, so let's go through them 🦋
The OR-set-timeout parameter for the OR-Entry-Timer 🔁
this period should be essentially longer than the maximum time for a frame to travel around the entire network 🌍 and by entire network they mean the network made up of subnetworks linked together with transparent bridges. when entries with OR-bit set keep getting created for a dual MAC station because of the timeout mechanism, this parameter sets how much time passes between the back-to-back requests sent to that station. if the state of the dual FDDI ring changes and an entry with LS-bit set could be created, this parameter also sets the maximum time until that new entry shows up (this is for when an entry couldn't be created by sending search frames). so, ngl, the OR-set-timeout parameter should be set to some 10 seconds ⏱️✨
The Hold-time parameter for the Hold-Timer 🫶
same energy here: this period should as well be essentially longer than the maximum time for a frame to travel around the entire network 🌐 when two stations talk for the very first time, they swap ARP frames and DMARP replies 💌 the Hold-time parameter decides how long it takes before load sharing is assumed to be set up after the LS-bit gets set. during that window, the frames mentioned above must have reached its destination 📬 and if an entry gets marked with the H-bit by mistake, fixing it takes a relatively long time (that's the Query time 😭). proposed dimension: several minutes 🕰️
The Query-time parameter for the Query-Timer 🔍
when an entry is marked with LS- and H-bit, it's assumed that load sharing can happen with the associated station 🤝 but to fix a wrong H-bit, the correctness of the H-bit gets checked again every so often, based on the Query-time parameter ✅ the check is whether a frame arrives that was sent by the secondary MAC to the secondary MAC address of the target station. (the target station confirms it got the query frame by sending back a hold frame 💜) to keep the query and hold frame traffic from getting out of hand, the Query-time should be set to several minutes 🧘♀️
9.5. Format of DMARP Frames 📦
here's the layout of a DMARP frame, field by field, bestie, so you know exactly what goes where 👀
fieldname length comment
--------------------------------------------------------------------
hardware type 16 bit 1 = "ethernet"
protocol type 16 bit 2048D = "Internet
Protocol"
length of hardware 8 bit Value in octets,
addresses 6 for 48 bit MAC addresses
length of protocol 8 bit Value in octets,
addresses 4 for Internet addresses
operation 16 bit 1: "reply"
2: "request"
3: "error"
4: "search"
5: "found"
6: "query"
7: "hold"
1. hardware address ... octets
2. hardware address ... octets
protocol address ... octets
sender
protocol address ... octets
receiver
--------------------------------------------------------------------the value for the field "protocol type" is the same as in ARP frames 🎀
9.6. Contents of DMARP Frames 🧩
in the tables below, the fields that hold the length and type of protocol and hardware addresses are left out, so don't panic when they're missing 🙈
Format:
+-------------------------------------------------------------+
| Operation | 1. hardware | 2. hardware | protocol | protocol |
| | address | address | address | address |
| | | | sender | receiver |
+-------------------------------------------------------------+Operation = 1 (reply), 2 (request), 3 (error):
+-----------------------------------------------------------------+
| Operation | P-MAC address | S-MAC address | protocol | protocol |
| | sender | sender | address | address |
| | | | sender | receiver |
+-----------------------------------------------------------------+Operation=4 (search):
+-------------------------------------------------------------------+
| Operation=4 | P-MAC | P-MAC address | protocol | broadcast |
| (search) | address | counter- | address | protocol |
| | sender | station | sender | address |
+-------------------------------------------------------------------+Operation=5 (found):
+-------------------------------------------------------------------+
| Operation=5 | P-MAC | S-MAC address | protocol | broadcast |
| (found) | address | counter- | address | protocol |
| | sender | station | sender | address |
+-------------------------------------------------------------------+
+-------------------------------------------------------------------+
| Operation=6 | S-MAC | P-MAC address | protocol | broadcast |
| (query) | address | counter- | address | protocol |
| | sender | station | sender | address |
+-------------------------------------------------------------------+Operation=7 (hold):
+-------------------------------------------------------------------+
| Operation=7 | P-MAC address | S-MAC address | protocol | protocol |
| (hold) | sender | sender | address | address |
| | | | sender | receiver |
+-------------------------------------------------------------------+okay so here's the routing drama 🚦 apart from the error frames, all frames are sent on the secondary ring. the reply, error and search frames are addressed to the broadcast hardware address 📢 and the request, found, query and hold frames are addressed to an individual secondary MAC address 💌
10. Formal Description 🎀
the following description is written in ESTELLE 💜
10.1. Global Constants, Variables and Types 🌸
default individual queue;
timescale ...;
type
PDU_type = ... ; (* format of a Protocol Data Unit:
String of variable length *)
HW_addr_type = ... ; (* format of a 48 bit MAC address *)
PR_addr_type = ... ; (* General: format of a protocol address
in an ARP or DMARP frame *)
IP_addr_type = ... ; (* General: format of an IP address *)
QoS_type = ... ; (* General: format of a Quality-of-
-Service statement *)
timer_name_type = ... ; (* Type for the name of a system timer *)
flag = (reset,set);
var
(*
The values of these variables are set in the initialization part or
by external management functions.
*)
My_P_MAC_addr : HW_addr_type; (* Address of the MAC, placed on
the primary ring *)
My_S_MAC_addr : HW_addr_type; (* Address of the MAC, placed on
the secondary ring *)
My_IP_address : IP_addr_type; (* IP address of this station *)
Broadcast_HW_addr : HW_addr_type; (* Broadcast MAC address (48 bit) *)
Broadcast_IP_addr : IP_addr_type; (* Broadcast IP address *)
dmarp_QoS : QoS_type; (* Quality_of_Service-statement
for DMARP frames *)
ethernet : integer; (* Type statement in DMARP frames *)
ip : integer; (* Number for IP as protocol type *)
fddi_addr_length : integer; (* Length of a MAC address in octetts *)
ip_addr_length : integer; (* Length of a IP address in octetts *)
OR_set_timeout : integer; (* Parameter for the OR-Entry-Timer *)
Query_time : integer; (* Parameter for the Hold-Timer *)
Hold_time : integer; (* Parameter for the Query-Timer *)10.2. Channels 📡
channel SAPchn(User,Provider);
by User :
UNITDATA_request
(
Source_addr : HW_addr_type;
Dest_addr : HW_addr_type;
QoS : QoS_type;
PDU : PDU_type;
)
by Provider :
UNITDATA_indication
(
Source_addr : HW_addr_type;
Dest_addr : HW_addr_type;
QoS : QoS_type;
PDU : PDU_type;
)
channel System_Access_Point_chn(User,Provider);
by User:
TIMER_request(Time : integer;
Timer_id : timer_name_type;
subscript : integer);
TIMER_cancel(Timer_id : timer_name_type;
subscript : integer);
by Provider:
TIMER_response(Timer_id : timer_name_type;
subscript : integer);10.3. The Module Header and Interaction Points 🧚
module LS_module systemprocess;
ip LS_ARPSAP : SAPchn(Provider);
LS_IPSAP : SAPchn(Provider);
SNAP1_ARPSAP : SAPchn(User);
SNAP1_LSSAP : SAPchn(User);
SNAP1_IPSAP : SAPchn(User);
SNAP2_ARPSAP : SAPchn(User);
SNAP2_LSSAP : SAPchn(User);
SNAP2_IPSAP : SAPchn(User);
LS_System_Access_Point : System_Access_Point_chn(User);
end;10.4. The Modulebody of the Load Sharing Entity 🫧
body LS_body for LS_module;
module multiplexer_module process;
ip LS_IPSAP : SAPchn(Provider);
SNAP1_IPSAP : SAPchn(User);
SNAP2_IPSAP : SAPchn(User);
end;
module cache_administration_module process;
ip LS_ARPSAP : SAPchn(Provider);
SNAP1_ARPSAP : SAPchn(User);
SNAP1_LSSAP : SAPchn(User);
SNAP2_ARPSAP : SAPchn(User);
SNAP2_LSSAP : SAPchn(User);
LS_System_Access_Point : System_Access_Point_chn(User);
end;
body cache_administration_body for cache_administration_module;
(* defined later *)
end;
body multiplexer_body for multiplexer_module;
(* defined later *)
end;
modvar
cache_administration : cache_administration_module;
multiplexer : multiplexer_module;
initialize
begin
ethernet := 1;
ip := 2048;
fddi_addr_length := 6;
ip_addr_length := 4;
init cache_administration with cache_administration_body;
init multiplexer with multiplexer_body;
attach LS_IPSAP to multiplexer.LS_IPSAP;
attach SNAP1_IPSAP to multiplexer.SNAP1_IPSAP;
attach SNAP2_IPSAP to multiplexer.SNAP2_IPSAP;
attach LS_ARPSAP to cache_administration.LS_ARPSAP;
attach SNAP1_ARPSAP to cache_administration.SNAP1_ARPSAP;
attach SNAP1_LSSAP to cache_administration.SNAP1_LSSAP;
attach SNAP2_ARPSAP to cache_administration.SNAP2_ARPSAP;
attach SNAP2_LSSAP to cache_administration.SNAP2_LSSAP;
attach LS_System_Access_Point to cache_administration.
LS_System_Access_Point;
end; end;10.5. The Modulebody for the Multiplexer 🦄
body multiplexer_body for multiplexer_module;
type
Type_of_addr_type = (individual, multi, broad);
ring_type = (primary, secondary);
var
act_S_MAC_addr : HW_addr_type;
function determ_addrtype(HW_addr: HW_addr_type): Type_of_addr_type;
primitive;
(*
Returns the type of a hardware address.
(Individual, multicast or broadcast address)
*)The multiplexer's get_cacheentry and ls_criteria declarations come first, then the transitions that decide whether a frame goes out as SNAP1 or SNAP2 🦋
function get_cacheentry(prtype: integer; P_MAC_addr: HW_addr_type;
var S_MAC_addr : HW_addr_type): boolean;
primitive;
(*
Returns the associated secondary MAC address for a given primary MAC
address and protocol type. If an entry exists, the value TRUE is
returned.
*)
function ls_criteria : ring_type;
(*
Returns the ring on which the actual frame should be transmitted.
*)
primitive;
trans
when LS_IPSAP.UNITDATA_request(Source_addr,Dest_addr,QoS,PDU) begin
if determ_addrtype(Dest_addr) <> individual then
output SNAP1_IPSAP.UNITDATA_request(Source_addr,Dest_addr,QoS,PDU);
else begin
if get_cacheentry(ip,Dest_addr,act_S_MAC_addr) and
(ls_criteria=secondary) then
output SNAP2_IPSAP.UNITDATA_request(My_S_MAC_addr,
act_S_MAC_addr,QoS,PDU);
else
output SNAP1_IPSAP.UNITDATA_request(Source_addr,Dest_addr,QoS,PDU);
end;
end;
when SNAP1_IPSAP.UNITDATA_indication(Source_addr,Dest_addr,QoS,PDU)
begin
output LS_IPSAP.UNITDATA_indication(Source_addr,Dest_addr,QoS,PDU);
end;
when SNAP2_IPSAP.UNITDATA_indication(Source_addr,Dest_addr,QoS,PDU)
begin
if determ_addrtype(Dest_addr) = individual then begin
Dest_addr := My_P_MAC_addr;
output LS_IPSAP.UNITDATA_indication(Source_addr,Dest_addr,QoS,PDU);
end;
end;10.6. The Modulebody for the Cache Administration 🧚
This is the cache administration module, where the ARP and DMARP PDUs get their types and the address cache gets looked after 💅 The body starts with the type declarations.
body cache_administration_body for cache_administration_module;
type
arp_pdu_type = record
hwtype : integer;
prtype : integer;
HW_length : integer;
PR_length : integer;
operation : (request,reply);
HW_sender : HW_addr_type;
PR_sender : PR_addr_type;
HW_receiver : HW_addr_type;
PR_receiver : PR_addr_type;
end;
dmarp_operation_type = (request,reply,error,search,found,query,hold);
dmarp_pdu_type = record
hwtype : integer;
prtype : integer;
HW_length : integer;
PR_length : integer;
operation : dmarpoperation_type;
HW_1 : HW_addr_type;
HW_2 : HW_addr_type;
PR_sender : PR_addr_type;
PR_receiver : PR_addr_type;
end;
var
arp_pdu : arp_pdu_type;
dmarp_pdu : dmarp_pdu_type;
send_pdu : dmarp_pdu_type;
act_P_MAC_addr : HW_addr_type;
function my_pr_address(prtype : integer ; praddr : PR_addr_type):
boolean;
(*
Returns TRUE, if praddr is my station address, the protocol type is
prtype. (2048d for the Internet protocol)
*)
primitive;
function get_my_pr_addr(prtype : integer) : PR_addr_type;
(*
Returns my station address, the protocol has the number prtype.
*)
function extract_arp_pdu(PDU : PDU_type) : arp_pdu_type;
(*
Returns the data contained in an ARP PDU as a record.
*)
primitive;
function extract_dmarp_pdu(PDU : PDU_type) : dmarp_pdu_type;
(*
Returns the data contained in an DMARP PDU as a record.
*)
primitive;
function assemble_dmarp_pdu(dmarp_pdu : dmarp_pdu_type): PDU;
(*
Returns a DMARP PDU from the data in the record.
*)
primitive;
procedure create_entry(prtype: integer; P_MAC_addr: HW_addr_type;
S_MAC_addr: HW_addr_type; LS_Bit: flag; OR_Bit: flag;
H_Bit: flag; Q_Bit: flag; R_Bit: flag; V_Bit: flag);
(*
Creates a new entry in the address cache, if no entry with the given
primary MAC address or R-bit set to one exists. The protocol type has
the number prtype. The control bits are set as given in the parameters,
the LS-bit is set last.
*)
primitive;
function search_entry(prtype : integer; P_MAC_addr : HW_addr_type):
boolean;
(*
Returns TRUE if an entry with the primary MAC address P_MAC_addr and
the given protocol type was found in the address cache.
*)
primitive;
procedure update_entry(prtype: integer; P_MAC_addr: HW_addr_type;
S_MAC_addr: HW_addr_type);
(*
Searches an entry with the given primary MAC address P_MAC_address and
updates the secondary MAC address in the entry if the R-bit is set to
zero.
*)
primitive;
procedure reset_LS_bit(prtype: integer; P_MAC_addr : HW_addr_type);
(*
Searches an entry with the given primary MAC address P_MAC_address and
resets the LS-bit if the R-bit is reset.
*)
primitive;
procedure set_Q_bit(prtype: integer; P_MAC_addr : HW_addr_type);
(*
Searches an entry with the given primary MAC address P_MAC_address and
sets the Q-bit if the R-bit is reset.
*)
primitive;
function H_bit_set(prtype: integer; P_MAC_addr : HW_addr_type):
boolean;
(*
Returns TRUE if an entry exists with H-bit set to one and the given
P-MAC address.
*)
primitive;
function OR_bit_set(prtype: integer; P_MAC_addr : HW_addr_type):
boolean;
(*
Returns TRUE if an entry exists with OR-bit set to one and the given
P-MAC address.
*)
primitive;
function LS_bit_set(prtype: integer; P_MAC_addr : HW_addr_type):
boolean;
(*
Returns TRUE if an entry exists with LS-bit set to one and the given
P-MAC address.
*)
primitive;
function Q_bit_set(prtype: integer; P_MAC_addr : HW_addr_type):
boolean;
(*
Returns TRUE if an entry exists with Q-bit set to one and the given
P-MAC address.
*)
primitive;
function get_subscript(prtype: integer; P_MAC_addr : HW_addr_type):
integer;
(*
Returns the subscipt number of an entry with the given primary MAC
address.
*)
primitive;
function get_broadcast_addr(prtype : integer): PR_addr_type;
(*
Returns the broadcast protocol address for the given protocol type.
*)
function get_P_MAC_addr(subscript : integer) : HW_addr_type;
(*
Returns the primary MAC address of the entry with the given subscript
number.
*)
primitive;
function get_S_MAC_addr(prtype: integer; P_MAC_addr: HW_addr_type):
HW_addr_type;
(*
Returns the secondary MAC address of the station with the given primary
MAC address.
*)
primitive;
procedure delete_entry(subscript : integer);
(*
Deletes the entry with the given subscript number if the R-bit is
reset.
*)
primitive;
function get_pr_type(subscript : integer) : integer;
(*
Returns the protocol type for the entry with the given subscript
number.
*)
primitive;
function get_pr_length(prtype : integer) : integer;
(*
Returns the length of a protocol address.
*)
primitive;
trans
when LS_ARPSAP.UNITDATA_request(Source_addr,Dest_addr,QoS,PDU)
begin
arp_pdu := extract_arp_pdu(PDU);
output SNAP1_ARPSAP.UNITDATA_request(Source_addr,Dest_addr,QoS,PDU);
dmarp_pdu.hwtype := ethernet;
dmarp_pdu.prtype := arp_pdu.prtype;
dmarp_pdu.HW_length := fddi_addr_length;
dmarp_pdu.PR_length := arp_pdu.PR_length;
dmarp_pdu.operation := reply;
dmarp_pdu.HW_1 := My_P_MAC_addr;
dmarp_pdu.HW_2 := My_S_MAC_addr;
dmarp_pdu.PR_sender := arp_pdu.PR_sender;
dmarp_pdu.PR_receiver := arp_pdu.PR_receiver;
PDU := assemble_dmarp_pdu(dmarp_pdu);
output SNAP2_LSSAP.UNITDATA_request(My_S_MAC_addr,Broadcast_HW_addr,
dmarp_QoS,PDU);
end;
when SNAP1_ARPSAP.UNITDATA_indication(Source_addr,Dest_addr,QoS,PDU)
begin
output LS_ARPSAP.UNITDATA_indication(Source_addr,Dest_addr,QoS,PDU);
end;
when SNAP2_ARPSAP.UNITDATA_indication(Source_addr,Dest_addr,QoS,PDU)
begin end;
when SNAP1_LSSAP.UNITDATA_indication(Source_addr,Dest_addr,QoS,PDU)
begin
dmarp_pdu := extract_dmarp_pdu(PDU);
if ((dmarp_pdu.operation = error) or (dmarp_pdu.operation = reply))
then begin
if my_pr_address(dmarp_pdu.prtype,dmarp_pdu.PR_receiver) then begin
if not H_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) then begin
if not OR_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) then begin
if LS_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) then begin
output LS_System_Access_point.TIMER_cancel(
"Hold_Timer",get_subscript(dmarp_pdu.prtype,dmarp_pdu.HW_1));
create_entry(dmarp_pdu.prtype,dmarp_pdu.HW_1,dmarp_pdu.HW_2,
reset,set,reset,reset,reset,set);
end;
output LS_System_Access_point.TIMER_request(
OR_set_timeout,"OR_Entry_Timer",
get_subscript(dmarp_pdu.prtype,dmarp_pdu.HW_1));
send_pdu.hwtype := ethernet;
send_pdu.prtype := dmarp_pdu.prtype;
send_pdu.HW_length := fddi_addr_length;
send_pdu.PR_length := dmarp_pdu.PR_length;
send_pdu.operation := search;
send_pdu.HW_1 := My_P_MAC_addr;
send_pdu.HW_2 := dmarp_pdu.HW_1;
send_pdu.PR_sender := get_my_pr_addr(dmarp_pdu.prtype);
send_pdu.PR_receiver := get_broadcast_addr(dmarp_pdu.prtype);
PDU := assemble_dmarp_pdu(dmarp_pdu);
output SNAP2_LSSAP.UNITDATA_request(
My_S_MAC_addr,Broadcast_HW_addr,dmarp_QoS,PDU);
end else begin
if dmarp_pdu.operation=error then
update_entry(dmarp_pdu.prtype,dmarp_pdu.HW_1,dmarp_pdu.HW_2);
end;
end else begin
if dmarp_pdu.operation = error then
update_entry(dmarp_pdu.prtype,dmarp_pdu.HW_1,dmarp_pdu.HW_2);
end;
end else begin
if my_pr_address(dmarp_pdu.prtype,dmarp_pdu.PR_sender) and
(dmarp_pdu.operation = reply) then begin
dmarp_pdu.operation := error;
PDU := assemble_dmarp_pdu(dmarp_pdu);
output SNAP1_LSSAP.UNITDATA_request(
My_P_MAC_addr,Broadcast_HW_addr,dmarp_QoS,PDU);
end else begin
if dmarp_pdu.operation=error and
search_entry(dmarp_pdu.prtype,dmarp_pdu.HW_1) then
update_entry(dmarp_pdu.prtype,dmarp_pdu.HW_1,dmarp_pdu.HW_2);
end; end; end; end;
when SNAP2_LSSAP.UNITDATA_indication(Source_addr,Dest_addr,QoS,PDU)begin
dmarp_pdu := extract_dmarp_pdu(PDU);
if (dmarp_pdu.operation = found) and
my_pr_address(dmarp_pdu.prtype,dmarp_pdu.PR_receiver) then begin
if not H_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) then begin
if OR_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) then begin
output LS_System_Access_Point.
TIMER_cancel("OR_Entry_Timer",
get_subscript(dmarp_pdu.prtype,dmarp_pdu.HW_1));
end;
if LS_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) then begin
output LS_System_Access_Point.
TIMER_cancel("Hold_Timer",
get_subscript(dmarp_pdu.prtype,dmarp_pdu.HW_1));
end;
create_entry(dmarp_pdu.prtype,dmarp_pdu.HW_1,dmarp_pdu.HW_2,
set,reset,set,reset,reset,set);
output LS_System_Access_Point.TIMER_request(Query_time,"Query_Timer",
get_subscript(dmarp_pdu.prtype,dmarp_pdu.HW_1));
end;
end else begin
if (dmarp_pdu.operation = reply) or
(dmarp_pdu.operation = request) then begin
if search_entry(dmarp_pdu.prtype,dmarp_pdu.HW_1) then
update_entry(dmarp_pdu.prtype,dmarp_pdu.HW_1,dmarp_pdu.HW_2);
end;
if (dmarp_pdu.operation=request) and
my_pr_address(dmarp_pdu.prtype,dmarp_pdu.PR_receiver) then begin
send_pdu.hwtype := dmarp_pdu.hwtype;
send_pdu.prtype := dmarp_pdu.prtype;
send_pdu.HW_length := fddi_addr_length;
send_pdu.PR_length := dmarp_pdu.PR_length;
send_pdu.operation := reply;
send_pdu.HW_1 := My_P_MAC_addr;
send_pdu.HW_2 := My_S_MAC_addr;
send_pdu.PR_sender := get_my_pr_addr(dmarp_pdu.prtype);
send_pdu.PR_receiver := dmarp_pdu.PR_sender;
PDU := assemble_dmarp_pdu(dmarp_pdu);
output SNAP2_LSSAP.UNITDATA_request(
My_S_MAC_addr,Broadcast_HW_addr,dmarp_QoS,PDU);
end else begin
if my_pr_address(dmarp_pdu.prtype,dmarp_pdu.pr_receiver) then begin
case dmarp_pdu.operation of
reply: begin
if not ( OR_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) or
LS_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) )then begin
create_entry(dmarp_pdu.prtype,dmarp_pdu.HW_1,dmarp_pdu.HW_2,
set,reset,reset,reset,reset,set);
output LS_System_Access_Point.TIMER_request(Hold_time,
"Hold_Timer",get_subscript(dmarp_pdu.prtype,dmarp_pdu.HW_1));
end;
end;
error: begin
if not ( OR_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) or
H_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) ) then begin
if LS_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) then
output LS_System_access_point.TIMER_cancel(
"Hold_Timer",get_subscript(dmarp_pdu.prtype,dmarp_pdu.HW_1));
create_entry(dmarp_pdu.prtype,dmarp_pdu.HW_1,dmarp_pdu.HW_2,
reset,set,reset,reset,reset,set);
output LS_System_access_point.TIMER_request(
OR_set_timeout,"OR_Entry_Timer",
get_subscript(dmarp_pdu.prtype,dmarp_pdu.HW_1));
send_pdu.hwtype := ethernet;
send_pdu.prtype := dmarp_pdu.prtype;
send_pdu.HW_length := fddi_addr_length;
send_pdu.PR_length := dmarp_pdu.PR_length;
send_pdu.operation := search;
send_pdu.HW_1 := My_P_MAC_addr;
send_pdu.HW_2 := dmarp_pdu.HW_1;
send_pdu.PR_sender := get_my_pr_addr(dmarp_pdu.prtype);
send_pdu.PR_receiver := get_broadcast_addr(dmarp_pdu.prtype);
PDU := assemble_dmarp_pdu(dmarp_pdu);
output SNAP2_LSSAP.UNITDATA_request(
My_S_MAC_addr,Broadcast_HW_addr,dmarp_QoS,PDU);
end;
end;
search: begin
if not (dmarp_pdu.HW_1=My_P_MAC_addr or
dmarp_pdu.HW_2=My_P_MAC_addr) then begin
if H_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) and
H_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_2) then begin
send_pdu.hwtype := ethernet;
send_pdu.prtype := dmarp_pdu.prtype;
send_pdu.HW_length := fddi_addr_length;
send_pdu.PR_length := dmarp_pdu.PR_length;
send_pdu.operation := found;
send_pdu.HW_1 := dmarp_pdu.HW_2;
send_pdu.HW_2 := get_S_MAC_addr(dmarp_pdu.prtype,
dmarp_pdu.HW_2);
send_pdu.PR_sender := get_my_pr_addr(dmarp_pdu.prtype);
send_pdu.PR_receiver := get_broadcast_addr(dmarp_pdu.prtype);
PDU := assemble_dmarp_pdu(send_pdu);
output SNAP2_LSSAP.UNITDATA_request(My_S_MAC_addr,
get_S_MAC_addr(dmarp_pdu.prtype,dmarp_pdu.HW_1),dmarp_QoS,PDU);
send_pdu.HW_1 := dmarp_pdu.HW_1;
send_pdu.HW_2 := get_S_MAC_addr(dmarp_pdu.prtype,
dmarp_pdu.HW_1);
PDU := assemble_dmarp_pdu(send_pdu);
output SNAP2_LSSAP.UNITDATA_request(My_S_MAC_addr,
get_S_MAC_addr(dmarp_pdu.prtype,dmarp_pdu.HW_2),dmarp_QoS,PDU);
end;
end;
end;
Query: begin
if dmarp_pdu.HW_2 = My_P_MAC_addr then begin
send_pdu.hwtype := ethernet;
send_pdu.prtype := dmarp_pdu.prtype;
send_pdu.HW_length := dmarp_pdu.HW_length;
send_pdu.PR_length := dmarp_pdu.PR_length;
send_pdu.operation := hold;
send_pdu.HW_1 := My_P_MAC_addr;
send_pdu.HW_2 := My_S_MAC_addr;
send_pdu.PR_sender := get_my_pr_addr(dmarp_pdu.prtype);
send_pdu.PR_receiver := dmarp_pdu.PR_sender;
PDU := assemble_dmarp_pdu(send_pdu);
output SNAP2_LSSAP.UNITDATA_request(
My_S_MAC_addr,dmarp_pdu.HW_1,dmarp_QoS,PDU);
end;
end;
Hold: begin
if H_bit_set(dmarp_pdu.prtype,dmarp_pdu.HW_1) then
reset_Q_bit(dmarp_pdu.prtype,dmarp_pdu.HW_1);
end;
end;
end;
end;
end;
end;
when LS_System_Access_Point.TIMER_response(Timer_name,subscript) begin
case Timer_name of
"OR_Entry_Timer": begin
act_P_MAC_addr := get_P_MAC_addr(subscript);
if OR_bit_set(get_pr_type(subscript),act_P_MAC_addr) then begin
send_pdu.hwtype := ethernet;
send_pdu.prtype := get_pr_type(subscript);
send_pdu.HW_length := fddi_addr_length;
send_pdu.PR_length := get_pr_length(send_pdu.prtype);
send_pdu.operation := request;
send_pdu.HW_1 := My_P_MAC_addr;
send_pdu.HW_2 := My_S_MAC_addr;
send_pdu.PR_sender := get_my_pr_addr(send_pdu.prtype);
send_pdu.PR_receiver := get_broadcast_addr(send_pdu.prtype);
PDU := assemble_dmarp_pdu(send_pdu);
output SNAP2_LSSAP.UNITDATA_request(
My_S_MAC_addr,get_S_MAC_addr(send_pdu.prtype,act_P_MAC_addr),
dmarp_QoS,PDU);
delete_entry(subscript);
end;
end;
"Hold_Timer": begin
act_P_MAC_addr := get_P_MAC_addr(subscript);
if (not H_bit_set(get_pr_type(subscript),act_P_MAC_addr)) and
LS_bit_set(get_pr_type(subscript),act_P_MAC_addr) then begin
set_H_bit(get_pr_type(subscript),act_P_MAC_addr);
output LS_System_Access_point.TIMER_request(
Query_time,"Query_Timer",subscript);
end;
end;
"Query_Timer": begin
act_P_MAC_addr := get_P_MAC_addr(subscript);
send_pdu.hwtype := ethernet;
send_pdu.prtype := get_pr_type(subscript);
send_pdu.HW_length := fddi_addr_length;
send_pdu.PR_length := get_pr_length(send_pdu.prtype);
send_pdu.PR_sender := get_my_pr_addr(send_pdu.prtype);
send_pdu.PR_receiver := get_broadcast_addr(send_pdu.prtype);
if Q_bit_set(get_pr_type(subscript),act_P_MAC_addr) then begin
send_pdu.HW_1 := My_P_MAC_addr;
send_pdu.HW_2 := My_S_MAC_addr;
send_pdu.operation := request;
PDU := assemble_dmarp_pdu(send_pdu);
output SNAP2_LSSAP.UNITDATA_request(
My_S_MAC_addr,get_S_MAC_addr(send_pdu.prtype,act_P_MAC_addr),
dmarp_QoS,PDU);
delete_entry(subscript);
end else begin
send_pdu.HW_1 := My_S_MAC_addr;
send_pdu.HW_2 := get_P_MAC_addr(subscript);
send_pdu.operation := query;
PDU := assemble_dmarp_pdu(send_pdu);
output SNAP2_LSSAP.UNITDATA_request(
My_S_MAC_addr,get_S_MAC_addr(send_pdu.prtype,send_pdu.HW_2),
dmarp_QoS,PDU);
set_Q_bit(send_pdu.prtype,send_pdu.HW_2);
end; end; end; end; end; (* body *)11. Summary ✨
okay bestie, the TL;DR is the load sharing layer is the star of the show 🌸 Adding it to the protocol layering of dual MAC stations is what lets IP and ARP run on inhomogeneous FDDI rings 🦋, so the ring doesn't have to be all one kind of setup. And single MAC stations? Their protocol suite needs no modification at all, so they just chill 💅
Next up, the "dual MAC" thing is basically invisible to ARP, IP, and the higher layer protocols. Main character energy for the load sharing layer 👑
Also, in dual MAC stations, any load sharing criteria may be implemented in the multiplexer of the load sharing entity 🎀. The load sharing entity is also the one handling the conversion of addresses, the exchange of address and reachability information between dual MAC stations, and the proper transmission of multicast and broadcast frames 🫶. It's a whole lot of responsibility, and it's giving reliable 😭🔥
12. References 📚
[1] ANSI, "FDDI Station Management (SMT)", ANSI X3T9/90-X3T9.5/84-49 Rev 6.2, May 1990.
[2] ANSI, "FDDI Media Access Control (MAC-2)", X3T9/90-X3T9.5/88-139 Rev 3.2, June 1990.
[3] ISO, "Information processing systems- Local area networks- Part 2: Logical link control", ISO 8802-2:1989, August 1989.
[4] IEEE, "Draft Standard P802.1A Overview and Architecture", P802.1A/D9-89/74, September 1989.
[5] Plummer, C., "An Ethernet Address Resolution Protocol --or-- Converting Network Protocol Addresses to 48.bit Ethernet Address for Transmission on Ethernet Hardware", RFC 826, MIT, November 1982.
[6] Reynolds, J., and Postel, J., "Assigned Numbers", RFC 1060, USC/Information Sciences Institute, March 1990.
[7] Postel, J., "Internet Protocol", RFC 791, USC/Information Sciences Institute, September 1981.
[8] Katz, D., "A Proposed Standard for the Transmission of IP Datagrams over FDDI Networks", RFC 1188, Merit/NSFNET, October 1990.
[9] Internet Engineering Task Force, Braden, R., Editor, "Requirements for Internet Hosts -- Communication Layers", RFC 1122, IETF, October 1989.
[10] Katz, D., "The Use of Connectionless Network Layer Protocols over FDDI Networks", Merit/NSFNET, 1990.
13. Security Considerations 🔒
bestie, this memo literally says security issues are not discussed in it 💀 Security issues are not discussed in this memo.
14. Author's Address 💌
Peter Kuehn
Raiffeisenstrasse 9b
8933 Untermeitingen
Germany
Phone: .. 82 32 / 7 46 02
EMail: thimmela@sniabg.wa.sni.de📦 where this page comes from
- ietf: rfc1329 1992-05
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms