draft-ietf-isis-restart-01.txt   draft-ietf-isis-restart-02.txt 
Network Working Group M. Shand Network Working Group M. Shand
Internet Draft Cisco Systems Internet Draft Cisco Systems
Expiration Date: November 2002 Expiration Date: May 2003
May 2002 Nov 2002
Restart signaling for ISIS Restart signaling for IS-IS
draft-ietf-isis-restart-01.txt draft-ietf-isis-restart-02.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1]. all provisions of Section 10 of RFC2026 [1].
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Internet-Drafts are draft documents valid for a maximum of Drafts. Internet-Drafts are draft documents valid for a maximum of
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Remaining Time (2 octets) Remaining Time (2 octets)
Remaining holding time (in seconds) Remaining holding time (in seconds)
(note: only required when RA bit is set) (note: only required when RA bit is set)
On receipt of an IIH with the "re-start" TLV having the RR bit set, On receipt of an IIH with the "re-start" TLV having the RR bit set,
if there exists on this interface an adjacency in state "Up" with if there exists on this interface an adjacency in state "Up" with
the same System ID, and in the case of a LAN circuit, with the same the same System ID, and in the case of a LAN circuit, with the same
source LAN address, then, irrespective of the other contents of the source LAN address, then, irrespective of the other contents of the
"Intermediate System Neighbors" option (LAN circuits), or the "Intermediate System Neighbors" option (LAN circuits), or the
"Point-to-Point Adjacency State" option (Point-to-Point circuits): - "Point-to-Point Adjacency State" option (Point-to-Point circuits): -
a) DO NOT refresh the timer on the adjacency, but leave the a) Do not change the state of the adjacency. It is an implementation
adjacency in state "Up", choice whether or not the holding time of the adjacency is
refreshed. Not refreshing the holding time preserves the intention
of the original holding time. Refreshing it may allow a longer
grace period for the completion of the restart process. Whichever
option is chosen, the "remaining time" transmitted according
to (b) below MUST reflect the actual time after which the
adjacency will now expire.
b) immediately (i.e. without waiting for any currently running timer b) immediately (i.e. without waiting for any currently running timer
interval to expire, but with a small random delay of a few 10s of interval to expire, but with a small random delay of a few 10s of
milliseconds on LANs to avoid "storms"), transmit over the milliseconds on LANs to avoid "storms"), transmit over the
corresponding interface an IIH including the "re-start" TLV with corresponding interface an IIH including the "re-start" TLV with
the RR bit clear and the RA bit set, having updated the "Point-to- the RR bit clear and the RA bit set, having updated the "Point-to-
Point Adjacency State" option to reflect any new values received Point Adjacency State" option to reflect any new values received
from the re-starting router. (This allows the restarting router to from the re-starting router. (This allows the restarting router to
quickly acquire the correct information to place in its hellos.) quickly acquire the correct information to place in its hellos.)
The "Remaining Time" MUST be set to the current time (in seconds) The "Remaining Time" MUST be set to the current time (in seconds)
before the holding timer on this adjacency is due to expire. This before the holding timer on this adjacency is due to expire. This
IIH SHOULD be transmitted before any LSPs or SNPs transmitted as a IIH SHOULD be transmitted before any LSPs or SNPs transmitted as a
result of the receipt of the original IIH. result of the receipt of the original IIH.
c) if the corresponding interface is a Point-to-Point interface, or c) if the corresponding interface is a Point-to-Point interface, or
if the receiving router has the highest LnRouterPriority (with if the receiving router has the highest LnRouterPriority (with
highest source MAC address breaking ties) among those routers highest source MAC address breaking ties) among those routers
whose IIHs contain the restart TLV, excluding the transmitting whose IIHs contain the restart TLV, excluding the transmitting
router (note the actual DR is NOT changed by this process.), router (note the actual DIS is NOT changed by this process.),
initiate the transmission over the corresponding interface of a initiate the transmission over the corresponding interface of a
complete set of CSNPs, and set SRMflags on the corresponding complete set of CSNPs, and set SRMflags on the corresponding
interface for all LSPs in the local LSP database. interface for all LSPs in the local LSP database.
Otherwise (i.e. if there was no adjacency in the "UP" state to the Otherwise (i.e. if there was no adjacency in the "UP" state to the
system ID in question), process the IIH as normal by re-initializing system ID in question), process the IIH as normal by re-initializing
the adjacency, and setting the RA bit in the returned IIH. the adjacency, and setting the RA bit in the returned IIH.
A router that does not support the re-start capability will ignore A router that does not support the re-start capability will ignore
the "re-start" TLV and re-initialize the adjacency as normal, the "re-start" TLV and re-initialize the adjacency as normal,
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On starting, a router initializes the timer T3, starts timer T2 for On starting, a router initializes the timer T3, starts timer T2 for
each LSPDB and for each interface (and in the case of a LAN circuit, each LSPDB and for each interface (and in the case of a LAN circuit,
for each level) starts a timer T1 and transmits an IIH containing for each level) starts a timer T1 and transmits an IIH containing
the "re-start" TLV with the RR bit set. the "re-start" TLV with the RR bit set.
On a Point-to-Point circuit the "Point-to-Point Adjacency State" On a Point-to-Point circuit the "Point-to-Point Adjacency State"
SHOULD be set to "Init", because the receipt of the acknowledging SHOULD be set to "Init", because the receipt of the acknowledging
IIH (with RA set) MUST cause the adjacency to enter "Up" state IIH (with RA set) MUST cause the adjacency to enter "Up" state
immediately. immediately.
On a LAN circuit the LAN-ID assigned to the circuit SHOULD be the
same as that used prior to the re-start. In particular, for any
circuits for which the re-starting router was previously DIS, the
use of a different LAN-ID would necessitate the generation of a new
set of pseudonode LSPs, and corresponding changes in all the LSPs
referencing them from other routers on the LAN. By preserving the
LAN-ID across the restart, this churn can be prevented.
Transmission of "normal" IIHs is inhibited until the conditions Transmission of "normal" IIHs is inhibited until the conditions
described below are met (in order to avoid causing an unnecessary described below are met (in order to avoid causing an unnecessary
adjacency re-initialization). On expiry of the timer T1, it is adjacency re-initialization). On expiry of the timer T1, it is
restarted and the IIH is re-transmitted as above. restarted and the IIH is re-transmitted as above.
On receipt of an IIH by the restarting router, a local adjacency is On receipt of an IIH by the restarting router, a local adjacency is
established as usual, and if the IIH contains a "re-start" TLV with established as usual, and if the IIH contains a "re-start" TLV with
the RA bit set, the receipt of the acknowledgement over that the RA bit set, the receipt of the acknowledgement over that
interface is noted. interface is noted.
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4.2.1 Multiple levels 4.2.1 Multiple levels
A router which is operating as both a level 1 and a level 2 router A router which is operating as both a level 1 and a level 2 router
on a particular interface MUST perform the above operations for each on a particular interface MUST perform the above operations for each
level. level.
On a LAN interface, it MUST send and receive both Level 1 and On a LAN interface, it MUST send and receive both Level 1 and
Level 2 IIHs and perform the CSNP synchronizations independently for Level 2 IIHs and perform the CSNP synchronizations independently for
each level. each level.
On a pt-pt interface, only as single IIH (indicating support for On a pt-pt interface, only a single IIH (indicating support for both
both levels) is required, but it MUST perform the CSNP levels) is required, but it MUST perform the CSNP synchronizations
synchronizations independently for each level. independently for each level.
4.3 Database synchronization 4.3 Database synchronization
When a router is started or re-started it can expect to receive a When a router is started or re-started it can expect to receive a
(set of) CSNP(s) over each interface. The arrival of the CSNP(s) is (set of) CSNP(s) over each interface. The arrival of the CSNP(s) is
now guaranteed, since the "re-start" IIH with the RR bit set will be now guaranteed, since the "re-start" IIH with the RR bit set will be
retransmitted until the CSNP(s) are correctly received. retransmitted until the CSNP(s) are correctly received.
The CSNPs describe the set of LSPs that are currently held by each The CSNPs describe the set of LSPs that are currently held by each
neighbor. Synchronization will be complete when all these LSPs have neighbor. Synchronization will be complete when all these LSPs have
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deterministic way, such that the same information occurs in the same deterministic way, such that the same information occurs in the same
place in the same LSP (and hence the LSPs are identical to their place in the same LSP (and hence the LSPs are identical to their
previous versions). If this can be achieved, the new versions will previous versions). If this can be achieved, the new versions will
not even cause SPF to be run in other systems. However, provided the not even cause SPF to be run in other systems. However, provided the
same information is included in the set of LSPs (albeit in a same information is included in the set of LSPs (albeit in a
different order, and possibly different LSPs), the result of running different order, and possibly different LSPs), the result of running
the SPF will be the same and will not cause churn to the forwarding the SPF will be the same and will not cause churn to the forwarding
tables. tables.
In the case of a re-starting router, none of the router's own non- In the case of a re-starting router, none of the router's own non-
pseudonode LSPs are transmitted, nor is the SPF run to update the pseudonode LSPs are transmitted, nor are the router's own forwarding
forwarding tables while the timer T3 is running. tables updated while the timer T3 is running.
Redistribution of inter-level information must be regenerated before Redistribution of inter-level information must be regenerated before
this router's LSP is flooded to other nodes. Therefore the level-n this router's LSP is flooded to other nodes. Therefore the level-n
non-pseudonode LSP(s) should not be flooded until the other level's non-pseudonode LSP(s) should not be flooded until the other level's
T2 timer has expired and its SPF has been run. This ensures that any T2 timer has expired and its SPF has been run. This ensures that any
inter-level information that should be propagated can be included in inter-level information that should be propagated can be included in
the level-n LSP(s). the level-n LSP(s).
During this period, if one of the router's own (including During this period, if one of the router's own (including
pseudonodes) LSPs is received, which the local router does not pseudonodes) LSPs is received, which the local router does not
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not be present in the global LSP database. However, in the present not be present in the global LSP database. However, in the present
circumstances, this would be highly undesirable, because it could circumstances, this would be highly undesirable, because it could
cause premature removal of an own LSP -- and hence churn in remote cause premature removal of an own LSP -- and hence churn in remote
routers. Even if the local system has one or more own LSPs (which it routers. Even if the local system has one or more own LSPs (which it
has generated, but not yet transmitted) it is still not valid to has generated, but not yet transmitted) it is still not valid to
compare the received LSP against this set, since it may be that as a compare the received LSP against this set, since it may be that as a
result of propagation between level 1 and level 2 (or vice versa) a result of propagation between level 1 and level 2 (or vice versa) a
further own LSP will need to be generated when the LSP databases further own LSP will need to be generated when the LSP databases
have synchronized. have synchronized.
When the timer T2 expires, or is cancelled, the SPF is run to update When the timer T2 expires, or is cancelled indicating that
the RIB and FIB. synchronization for that level is complete, the SPF for that level
is run in order to derive any information which is required to be
propagated to another level, but the forwarding tables are not yet
updated.
Once the other level's SPF has run and any inter-level propagation Once the other level's SPF has run and any inter-level propagation
has been resolved, the 'own' LSPs can be generated and flooded. Any has been resolved, the 'own' LSPs can be generated and flooded. Any
'own' LSPs which were previously ignored, but which are not part of 'own' LSPs which were previously ignored, but which are not part of
the current set of 'own' LSPs (including pseudonodes) should then be the current set of 'own' LSPs (including pseudonodes) should then be
purged. Note that it is possible that a Designated Router change may purged. Note that it is possible that a Designated Router change may
have taken place, and consequently the router should purge those have taken place, and consequently the router should purge those
pseudonode LSPs which it previously owned, but which are now no pseudonode LSPs which it previously owned, but which are now no
longer part of its set of pseudonode LSPs. longer part of its set of pseudonode LSPs.
When all the T2 timers have expired or been cancelled, the timer T3
is cancelled and the local forwarding tables are updated.
If the timer T3 expires before all the T2 timers have expired, this If the timer T3 expires before all the T2 timers have expired, this
indicates that the synchronization process is taking longer than indicates that the synchronization process is taking longer than
minimum holding time of the neighbors. The router's own LSP(s) for minimum holding time of the neighbors. The router's own LSP(s) for
levels which have not yet completed their first SPF computation are levels which have not yet completed their first SPF computation are
then flooded with the overload bit set to indicate that the router's then flooded with the overload bit set to indicate that the router's
LSPDB is not yet synchronized (and other routers should therefore LSPDB is not yet synchronized (and other routers should therefore
not compute routes through this router). In order to prevent the not compute routes through this router). In order to prevent the
neighbor's adjacencies from expiring, IIHs with the normal interface neighbor's adjacencies from expiring, IIHs with the normal interface
value for the holding time are transmitted over all interfaces with value for the holding time are transmitted over all interfaces with
 End of changes. 

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