draft-ietf-isis-restart-03.txt   draft-ietf-isis-restart-04.txt 
Network Working Group M. Shand Network Working Group M. Shand
Internet Draft Les Ginsberg Internet Draft Les Ginsberg
Expiration Date: September 2003 Cisco Systems Expiration Date: January 2004 Cisco Systems
March 2003 July 2003
Restart signaling for IS-IS Restart signaling for IS-IS
draft-ietf-isis-restart-03.txt draft-ietf-isis-restart-04.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
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skipping to change at page 1, line 32 skipping to change at page 1, line 32
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
1. Abstract 1. Abstract
The IS-IS routing protocol (RFC 1142 [2], ISO/IEC 10589 [3]) is a The IS-IS routing protocol (RFC 1195 [2], ISO/IEC 10589 [3]) is a
link state intra-domain routing protocol. Normally, when an IS-IS link state intra-domain routing protocol. Normally, when an IS-IS
router is restarted, the neighboring routers detect the restart router is restarted, temporary disruption of routing occurs due to
event and cycle their adjacencies with the restarting router through events in both the restarting router and the neighbors of the
the down state. This is necessary in order to invoke the protocol
mechanisms to ensure correct synchronization of the LSP database.
However, the cycling of the adjacency state causes the neighbors to
regenerate their LSPs describing the adjacency concerned. This in
turn causes temporary disruption of routes passing through the
restarting router. restarting router.
In certain scenarios such temporary disruption of the routes is The router which has been restarted computes its own routes before
highly undesirable. achieving database synchronization with its neighbors. The results
of this computation are likely to be non-convergent with the routes
This draft describes a mechanism for a restarting router to signal computed by other routers in the area/domain.
that it is restarting to its neighbors, and allow them to
reestablish their adjacencies without cycling through the down
state, while still correctly initiating database synchronization.
When such a router is restarted, it is highly desirable that it does
not recompute its own routes until it has achieved database
synchronization with its neighbors. Recomputing its routes before
synchronization is achieved will result in its own routes being
temporarily incorrect.
This draft additionally describes a mechanism for a restarting Neighbors of the restarting router detect the restart event and
router to determine when it has achieved synchronization with its cycle their adjacencies with the restarting router through the down
neighbors. state. The cycling of the adjacency state causes the neighbors to
regenerate their LSPs describing the adjacency concerned. This in
turn causes temporary disruption of routes passing through the
restarting router.
This draft additionally describes a mechanism to optimize database In certain scenarios the temporary disruption of the routes is
synchronization and minimize transient routing disruption when a highly undesirable. This draft describes mechanisms to avoid or
router starts. minimize the disruption due to both of these causes.
2. Conventions used in this document 2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC-2119 [4]. this document are to be interpreted as described in RFC-2119 [3].
If the control and forwarding functions in a router can be If the control and forwarding functions in a router can be
maintained independently, it is possible for the forwarding function maintained independently, it is possible for the forwarding function
state to be maintained across a control function restart. This state to be maintained across a control function restart. This
functionality is assumed when the terms "restart/restarting" are functionality is assumed when the terms "restart/restarting" are
used in this document. used in this document.
The terms "start/starting" are used to refer to a router in which The terms "start/starting" are used to refer to a router in which
the control function has either been started for the first time or the control function has either been started for the first time or
has been restarted but the forwarding functions have not been has been restarted but the forwarding functions have not been
maintained in a prior state. maintained in a prior state.
The terms "(re)start/(re)starting" are used when the text is The terms "(re)start/(re)starting" are used when the text is
applicable to both a "starting" and a "restarting" router. applicable to both a "starting" and a "restarting" router.
3. Overview 3. Overview
There are two related problems with the existing specification of When an adjacency is reinitialized as a result of a neighbor
IS-IS with regard to synchronization of LSP databases when a router restarting, a router does three things:
is restarted.
Firstly, when a routing process restarts and an adjacency to a
neighboring router is reinitialized the neighboring routing process
does three things:
1. It reinitializes the adjacency and causes its own LSP(s) to be 1. It causes its own LSP(s) to be regenerated, thus triggering
regenerated, thus triggering SPF runs throughout the area (or SPF runs throughout the area (or in the case of Level 2,
in the case of Level 2, throughout the domain). throughout the domain).
2. It sets SRMflags on its own LSP database on the adjacency 2. It sets SRMflags on its own LSP database on the adjacency
concerned. concerned.
3. In the case of a Point-to-Point link it transmits a (set of) 3. In the case of a Point-to-Point link it transmits a (set of)
CSNP(s) over the adjacency. CSNP(s) over the adjacency.
In the case of a restarting router process, the first of these is In the case of a restarting router process, the first of these is
highly undesirable, but the second is essential in order to ensure highly undesirable, but the second is essential in order to ensure
synchronization of the LSP database. synchronization of the LSP database.
Secondly, whether or not the router is being restarted, it is The third action above minimizes the number of LSPs which must be
desirable to be able to determine when the LSP databases of the exchanged and, if made reliable, provides a means of determining
neighboring routers have been synchronized (so that the overload bit when the LSP databases of the neighboring routers have been
can be cleared in the router's own LSP, for example). This document synchronized. This is desirable whether the router is being
describes modifications to achieve this. restarted or not (so that the overload bit can be cleared in the
router's own LSP, for example).
It is assumed that the three-way handshake [5] is being used on This draft describes a mechanism for a restarting router to signal
that it is restarting to its neighbors, and allow them to
reestablish their adjacencies without cycling through the down
state, while still correctly initiating database synchronization.
This draft additionally describes a mechanism for a restarting
router to determine when it has achieved LSP database
synchronization with its neighbors.
This draft additionally describes a mechanism to optimize LSP
database synchronization and minimize transient routing disruption
when a router starts.
It is assumed that the three-way handshake [4] is being used on
Point-to-Point circuits. Point-to-Point circuits.
4. Approach 4. Approach
4.1 Timers 4.1 Timers
Three additional timers, T1, T2 and T3 are required to support the Three additional timers, T1, T2 and T3 are required to support the
functionality defined in this document. functionality defined in this document.
An instance of T1 is maintained per interface, and indicates the An instance of the timer T1 is maintained per interface, and
time after which an unacknowledged (re)start attempt will be indicates the time after which an unacknowledged (re)start attempt
repeated. A typical value might be 3 seconds. will be repeated. A typical value might be 3 seconds.
An instance of T2 is maintained for each LSP database present in the An instance of the timer T2 is maintained for each LSP database
system i.e. for a Level1/2 system, there will be an instance of T2 present in the system i.e. for a Level1/2 system, there will be an
for Level 1 and an instance for Level 2. This is the maximum time instance of the timer T2 for Level 1 and an instance for Level 2.
that the system will wait for LSPDB synchronization. A typical value This is the maximum time that the system will wait for LSPDB
might be 60 seconds. synchronization. A typical value might be 60 seconds.
A single instance of T3 is maintained for the entire system. It A single instance of the timer T3 is maintained for the entire
indicates the time after which the router will declare that it has system. It indicates the time after which the router will declare
failed to achieve database synchronization (by setting the overload that it has failed to achieve database synchronization (by setting
bit in its own LSP). This is initialized to 65535 seconds, but is the overload bit in its own LSP). This is initialized to 65535
set to the minimum of the remaining times of received IIHs seconds, but is set to the minimum of the remaining times of
containing a restart TLV with RA set. received IIHs containing a restart TLV with RA set and an indication
that the neighbor has an adjacency in the UP state to the restarting
router.
NOTE: The timer T3 is only used by a restarting router.
4.2 Restart TLV 4.2 Restart TLV
A new TLV is defined to be included in IIH PDUs. The presence of A new TLV is defined to be included in IIH PDUs. The presence of
this TLV indicates that the sender supports the functionality this TLV indicates that the sender supports the functionality
defined in this document and it carries flags that are used to defined in this document and it carries flags that are used to
convey information during a (re)start. All IIHs transmitted by a convey information during a (re)start. All IIHs transmitted by a
router that supports this capability MUST include this TLV. router that supports this capability MUST include this TLV.
Type 211 Type 211
Length 3 Length 1 - (3 + ID Length)
Value (3 octets) Value
Flags (1 octet) Flags (1 octet)
Bit 1 - Restart Request (RR)
Bit 2 - Restart Acknowledgment (RA) 0 1 2 3 4 5 6 7
Bit 3 Suppress adjacency advertisement(SA) +--+--+--+--+--+--+--+--+
Bits 4-8 Reserved | Reserved |SA|RA|RR|
+--+--+--+--+--+--+--+--+
RR - Restart Request
RA - Restart Acknowledgment
SA - Suppress adjacency advertisement
(Note: Remaining fields are required when RA bit is set)
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)
Restarting Neighbor System ID (ID Length octets)
The system ID of the neighbor to which the RA refers.
Note: Implementations based on earlier versions of this
document may not include this field in the TLV when RA is
set. In this case a router which is expecting an RA on a
LAN circuit SHOULD assume that the acknowledgement is
directed at the local system.)
4.2.1 Use of RR and RA bits 4.2.1 Use of RR and RA bits
The RR bit is used by a (re)starting router to signal to its The RR bit is used by a (re)starting router to signal to its
neighbors that a (re)start is in progress, that an existing neighbors that a (re)start is in progress, that an existing
adjacency should be maintained even under circumstances when the adjacency SHOULD be maintained even under circumstances when the
normal operation of the adjacency state machine would require the normal operation of the adjacency state machine would require the
adjacency to be reinitialized, and to request a set of CSNPs. adjacency to be reinitialized, to request a set of CSNPs, and to
request setting of SRMflags.
The RA bit is sent by the neighbor of a (re)starting router to The RA bit is sent by the neighbor of a (re)starting router to
acknowledge the receipt of a restart TLV with the RR bit set. acknowledge the receipt of a restart TLV with the RR bit set.
When the neighbor of a (re)starting router receives an IIH with the When the neighbor of a (re)starting router receives an IIH with the
restart TLV having the RR bit set, if there exists on this interface restart TLV having the RR bit set, if there exists on this interface
an adjacency in state "Up" with the same System ID, and in the case an adjacency in state "Up" with the same System ID, and in the case
of a LAN circuit, with the same source LAN address, then, of a LAN circuit, with the same source LAN address, then,
irrespective of the other contents of the "Intermediate System irrespective of the other contents of the "Intermediate System
Neighbors" option (LAN circuits), or the "Point-to-Point Adjacency Neighbors" option (LAN circuits), or the "Point-to-Point Three-Way
State" option (Point-to-Point circuits): Adjacency" option (Point-to-Point circuits):
a) The state of the adjacency is not changed. It is an a) The state of the adjacency is not changed. If this is the first
implementation choice whether or not the holding time of the IIH with the RR bit set that this system has received associated
adjacency is refreshed. Not refreshing the holding time preserves with this adjacency then the adjacency is marked as being in
the intention of the original holding time. Refreshing it may "Restart mode" and the adjacency holding time is refreshed -
allow a longer grace period for the completion of the (re)start otherwise the holding time is not refreshed. The "remaining time"
process. Whichever option is chosen, the "remaining time"
transmitted according to (b) below MUST reflect the actual time transmitted according to (b) below MUST reflect the actual time
after which the adjacency will now expire. after which the adjacency will now expire. Receipt of a normal
IIH with RR bit reset will clear the "Restart mode" state. This
procedure allows the restarting router to cause the neighbor to
maintain the adjacency long enough for restart to successfully
complete while also preventing repetitive restarts from
maintaining an adjacency indefinitely. Whether an adjacency is
marked as being in "Restart mode" or not has no effect on
adjacency state transitions.
b) immediately (i.e. without waiting for any currently running timer b) immediately (i.e. without waiting for any currently running
interval to expire, but with a small random delay of a few 10s of timer interval to expire, but with a small random delay of a few
milliseconds on LANs to avoid "storms"), transmit over the 10s of milliseconds on LANs to avoid "storms"), transmit over the
corresponding interface an IIH including the restart TLV with the corresponding interface an IIH including the restart TLV with the
RR bit clear and the RA bit set, having updated the "Point-to- RR bit clear and the RA bit set, in the case of Point-to-Point
Point Adjacency State" option to reflect any new values received adjacencies having updated the "Point-to-Point Three-Way
from the (re)starting router. (This allows a restarting router to Adjacency" option to reflect any new values received from the
quickly acquire the correct information to place in its hellos.) (re)starting router. (This allows a restarting router to quickly
The "Remaining Time" MUST be set to the current time (in seconds) acquire the correct information to place in its hellos.) The
before the holding timer on this adjacency is due to expire. This "Remaining Time" MUST be set to the current time (in seconds)
IIH SHOULD be transmitted before any LSPs or SNPs transmitted as a before the holding timer on this adjacency is due to expire. If
result of the receipt of the original IIH. the corresponding interface is a LAN interface, then the
Restarting Neighbor System ID SHOULD be set to the System ID of
the router from whom the IIH with RR bit set was received. This
is required to correctly associate the acknowledgement and
holding time in the case where multiple systems on a LAN restart
at approximately the same time. This IIH SHOULD be transmitted
before any LSPs or SNPs transmitted as a 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 to
whose IIHs contain the restart TLV, excluding the transmitting which the receiving router has an adjacency in state "Up" on this
router (note the actual DIS is NOT changed by this process.), interface whose IIHs contain the restart TLV, excluding
initiate the transmission over the corresponding interface of a adjacencies to all routers which are considered in "Restart mode"
complete set of CSNPs, and set SRMflags on the corresponding (note the actual DIS is NOT changed by this process), initiate
interface for all LSPs in the local LSP database. the transmission over the corresponding interface of a complete
set of CSNPs, and set SRMflags on the corresponding 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 reinitializing system ID in question), process the IIH as normal by reinitializing
the adjacency, and setting the RA bit in the returned IIH. the adjacency, and setting the RA bit in the returned IIH.
4.2.2 Use of SA bit 4.2.2 Use of SA bit
The SA bit is used by a starting router to request that its neighbor The SA bit is used by a starting router to request that its neighbor
suppress advertisement of the adjacency to the starting router in suppress advertisement of the adjacency to the starting router in
the neighbors LSPs. the neighbor's LSPs.
A router which is starting has no maintained forwarding function A router which is starting has no maintained forwarding function
state. This may or may not be the first time the router has started. state. This may or may not be the first time the router has started.
If this is not the first time the router has started, copies of LSPs If this is not the first time the router has started, copies of LSPs
generated by this router in its previous incarnation may exist in generated by this router in its previous incarnation may exist in
the LSP databases of other routers in the network. These copies are the LSP databases of other routers in the network. These copies are
likely to appear "newer" than LSPs initially generated by the likely to appear "newer" than LSPs initially generated by the
starting router due to the reinitialization of LSP fragment sequence starting router due to the reinitialization of LSP fragment sequence
numbers by the starting router. This may cause temporary blackholes numbers by the starting router. This may cause temporary blackholes
to occur until the normal operation of the update process causes the to occur until the normal operation of the update process causes the
starting router to regenerate and flood copies of its own LSPs with starting router to regenerate and flood copies of its own LSPs with
higher sequence numbers. The temporary blackholes can be avoided if higher sequence numbers. The temporary blackholes can be avoided if
the starting router's neighbors suppress advertising an adjacency to the starting router's neighbors suppress advertising an adjacency to
the starting router until the starting router has been able to the starting router until the starting router has been able to
propagate newer versions of LSPs generated by previous incarnations. propagate newer versions of LSPs generated by previous incarnations.
When the neighbor of a starting router receives an IIH with the When the neighbor of a starting router receives an IIH with the
restart TLV having the SA bit set, if there exists on this interface restart TLV having the SA bit set, if there exists on this interface
an adjacency in state "Up" with the same System ID, and in the case an adjacency in state "Up" with the same System ID, and in the case
of a LAN circuit, with the same source LAN address, then of a LAN circuit, with the same source LAN address, then
advertisement of the adjacency to the starting router in LSPs should advertisement of the adjacency to the starting router in LSPs MUST
be suppressed. Until an IIH with the SA bit clear has been received, be suppressed. Until an IIH with the SA bit clear has been received,
the adjacency advertisement should continue to be suppressed. If the the adjacency advertisement MUST continue to be suppressed. If the
adjacency transitions to the UP state, the new adjacency should not adjacency transitions to the UP state, the new adjacency MUST NOT be
be advertised until an IIH with the SA bit clear has been received. advertised until an IIH with the SA bit clear has been received.
Note that a router which suppresses advertisement of the adjacency
to the starting router MUST NOT use this adjacency when performing
its SPF calculation. In particular, if an implementation follows the
example guidelines presented in [3] Annex C.2.5 Step 0:b) "pre-load
TENT with the local adjacency database", the suppressed adjacency
MUST NOT be loaded into the TENT.
4.3 Adjacency (re)acquisition 4.3 Adjacency (re)acquisition
Adjacency (re)acquisition is the first step in (re)initialization. Adjacency (re)acquisition is the first step in (re)initialization.
Both restarting and starting routers will make use of the RR bit in Restarting and starting routers will make use of the RR bit in the
the restart TLV, though at different stages of the (re)start restart TLV, though each will use it at different stages of the
procedure. (re)start procedure.
4.3.1 Adjacency reacquisition during restart 4.3.1 Adjacency reacquisition during restart
The restarting router explicitly notifies its neighbor that the The restarting router explicitly notifies its neighbor that the
adjacency is being reacquired, and hence that it should not adjacency is being reacquired, and hence that it SHOULD NOT
reinitialize the adjacency. This is achieved by setting the RR bit reinitialize the adjacency. This is achieved by setting the RR bit
in the restart TLV. When the neighbor of a restarting router in the restart TLV. When the neighbor of a restarting router
receives an IIH with the restart TLV having the RR bit set, if there receives an IIH with the restart TLV having the RR bit set, if there
exists on this interface an adjacency in state "Up" with the same 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 source System ID, and in the case of a LAN circuit, with the same source
LAN address, then the procedures described in 4.2.1 are followed. LAN address, then the procedures described in 4.2.1 are followed.
A router that does not support the restart capability will ignore A router that does not support the restart capability will ignore
the restart TLV and reinitialize the adjacency as normal, returning the restart TLV and reinitialize the adjacency as normal, returning
an IIH without the restart TLV. an IIH without the restart TLV.
On restarting, a router initializes the timer T3, starts timer T2 On restarting, a router initializes the timer T3, starts the timer
for each LSPDB and for each interface (and in the case of a LAN T2 for 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 circuit, for each level) starts the timer T1 and transmits an IIH
containing the restart TLV with the RR bit set. containing the restart 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 "Adjacency Three-Way State" SHOULD
SHOULD be set to "Init", because the receipt of the acknowledging be set to "Init", because the receipt of the acknowledging IIH (with
IIH (with RA set) MUST cause the adjacency to enter "Up" state 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 On a LAN circuit the LAN-ID assigned to the circuit SHOULD be the
same as that used prior to the restart. In particular, for any same as that used prior to the restart. In particular, for any
circuits for which the restarting router was previously DIS, the use circuits for which the restarting router was previously DIS, the use
of a different LAN-ID would necessitate the generation of a new set of a different LAN-ID would necessitate the generation of a new set
of pseudonode LSPs, and corresponding changes in all the LSPs of pseudonode LSPs, and corresponding changes in all the LSPs
referencing them from other routers on the LAN. By preserving the referencing them from other routers on the LAN. By preserving the
LAN-ID across the restart, this churn can be prevented. To enable a LAN-ID across the restart, this churn can be prevented. To enable a
restarting router to learn the LAN-ID used prior to restart, the restarting router to learn the LAN-ID used prior to restart, the
LAN-ID specified in an IIH w RR set MUST be ignored. LAN-ID specified in an IIH w RR set MUST be ignored.
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 reinitialization). On expiry of the timer T1, it is adjacency initialization). On expiry of the timer T1, it is
restarted and the IIH is retransmitted as above. restarted and the IIH is retransmitted as above.
On receipt of an IIH by the restarting router, a local adjacency is When a restarting router receives an IIH a local adjacency is
established as usual, and if the IIH contains a restart TLV with the established as usual, and if the IIH contains a restart TLV with the
RA bit set, the receipt of the acknowledgement over that interface RA bit set (and on LAN circuits with a Restart Neighbor System ID
is noted. which matches that of the local system), the receipt of the
acknowledgement over that interface is noted. When the RA bit is set
and the state of the remote adjacency is UP then the timer T3 is set
to the minimum of its current value and the value of the "Remaining
Time" field in the received IIH.
T3 is set to the minimum of its current value and the value of the On a Point-to-Point link, receipt of an IIH not containing the
"Remaining Time" field in the received IIH. restart TLV is also treated as an acknowledgement, since it
indicates that the neighbor is not restart capable. However, since
no CSNP is guaranteed to be received over this interface, the timer
T1 is cancelled immediately without waiting for a complete set of
CSNP(s). Synchronization may therefore be deemed complete even
though there are some LSPs which are held (only) by this neighbor
(see section 4.4). In this case we also want to be certain that the
neighbor will reinitialize the adjacency in order to guarantee that
SRMflags have been set on its database, thus ensuring eventual LSPDB
synchronization. This is guaranteed to happen except in the case
where the Adjacency Three-Way State in the received IIH is UP and
the Neighbor Extended Local Circuit ID matches the extended local
circuit ID assigned by the restarting router. In this case the
restarting router MUST force the adjacency to reinitialize by
setting the local Adjacency Three-Way State to DOWN and sending a
normal IIH.
Receipt of an IIH not containing the restart TLV is also treated as In the case of a LAN interface, receipt of an IIH not containing the
an acknowledgement, since it indicates that the neighbor is not restart TLV is unremarkable since synchronization can still occur so
restart capable. In this case the neighbor will have reinitialized long as at least one of the non-restarting neighboring routers on
the adjacency as normal, which in the case of a Point-to-Point link the LAN supports restart. Therefore T1 continues to run in this
will guarantee that SRMflags have been set on its database, thus case. If none of the neighbors on the LAN are restart capable, T1
ensuring eventual LSPDB synchronization. In the case of a LAN will eventually expire after the locally defined number of retries.
interface, the usual operation of the update process will also
ensure that synchronization is eventually achieved. However, since
no CSNP is guaranteed to be received over this interface, T1 is
cancelled immediately without waiting for a CSNP. Synchronization
may therefore be deemed complete even though there are some LSPs
which are held(only) by this neighbor (see section 4.4).
In the case of a Point-to-Point circuit, the "LocalCircuitID" and In the case of a Point-to-Point circuit, the "LocalCircuitID" and
"Extended Local Circuit ID" information contained in the IIH can be "Extended Local Circuit ID" information contained in the IIH can be
used immediately to generate an IIH containing the correct 3-way used immediately to generate an IIH containing the correct 3-way
handshake information. The presence of "Neighbor System ID" or handshake information. The presence of "Neighbor System ID" or
"Neighbor Extended Local Circuit ID" information which does not "Neighbor Extended Local Circuit ID" information which does not
match the values currently in use by the local system is ignored match the values currently in use by the local system is ignored
(since the IIH may have been transmitted before the neighbor had (since the IIH may have been transmitted before the neighbor had
received the new values from the restarting router), but the received the new values from the restarting router), but the
adjacency remains in the initializing state until the correct adjacency remains in the initializing state until the correct
information is received. information is received.
In the case of a LAN circuit the information in the Intermediate In the case of a LAN circuit the source neighbor information (e.g.
Systems Neighbors option is recorded and used for the generation of SNPAAddress) is recorded and used for adjacency establishment and
subsequent IIHs as normal. maintenance as normal.
When BOTH a complete set of CSNP(s) (for each active level, in the When BOTH a complete set of CSNP(s) (for each active level, in the
case of a pt-pt circuit) and an acknowledgement have been received case of a pt-pt circuit) and an acknowledgement have been received
over the interface, the timer T1 is cancelled. over the interface, the timer T1 is cancelled.
Once T3 has expired or been cancelled, subsequent IIHs are Once the timer T3 has expired or been cancelled, subsequent IIHs are
transmitted according to the normal algorithms, but including the transmitted according to the normal algorithms, but including the
restart TLV with both RR and RA clear. restart TLV with both RR and RA clear.
If a LAN contains a mixture of systems, only some of which support If a LAN contains a mixture of systems, only some of which support
the new algorithm, database synchronization is still guaranteed, but the new algorithm, database synchronization is still guaranteed, but
the "old" systems will have reinitialized their adjacencies. the "old" systems will have reinitialized their adjacencies.
If an interface is active, but does not have any neighboring router If an interface is active, but does not have any neighboring router
reachable over that interface the timer T1 would never be cancelled, reachable over that interface the timer T1 would never be cancelled,
and according to clause 4.4.1.1 the SPF would never be run. and according to clause 4.4.1.1 the SPF would never be run.
Therefore timer T1 is cancelled after some pre-determined number of Therefore timer T1 is cancelled after some pre-determined number of
expirations (which MAY be 1). (By this time any existing adjacency expirations (which MAY be 1). (By this time any existing adjacency
on a remote system would probably have expired anyway.) on a remote system would probably have expired anyway.)
A router which supports restart SHOULD ensure that the holding time
of any IIHs it transmits is greater than the expected time to
complete a restart. However, where this is impracticable or
undesirable a router MAY transmit one or more normal IIHs
(containing a restart TLV with RR and RA clear) after the initial
RR/RA exchange, but before synchronization has been achieved, in
order to extend the holding time of the neighbors adjacencies beyond
that indicated in the remaining time field of the neighbors IIH with
the RA bit set.
4.3.2 Adjacency acquisition during start 4.3.2 Adjacency acquisition during start
The starting router wants to ensure that in the event a neighboring The starting router wants to ensure that in the event a neighboring
router has an adjacency to the starting router in the UP state (from router has an adjacency to the starting router in the UP state (from
a previous incarnation of the starting router) that this adjacency a previous incarnation of the starting router) that this adjacency
is reinitialized. The starting router also wants neighboring routers is reinitialized. The starting router also wants neighboring routers
to suppress advertisement of an adjacency to the starting router to suppress advertisement of an adjacency to the starting router
until LSP database synchronization is achieved. This is achieved by until LSP database synchronization is achieved. This is achieved by
sending IIHs with the RR bit clear and the SA bit set in the restart sending IIHs with the RR bit clear and the SA bit set in the restart
TLV. The RR bit remains clear and the SA bit remains set in TLV. The RR bit remains clear and the SA bit remains set in
skipping to change at page 8, line 26 skipping to change at page 9, line 41
UP state and the initial T1 timer interval (see below) has expired. UP state and the initial T1 timer interval (see below) has expired.
Receipt of an IIH with RR bit clear will result in the neighboring Receipt of an IIH with RR bit clear will result in the neighboring
router utilizing normal operation of the adjacency state machine. router utilizing normal operation of the adjacency state machine.
This will ensure that any old adjacency on the neighboring router This will ensure that any old adjacency on the neighboring router
will be reinitialized. will be reinitialized.
On receipt of an IIH with SA bit set the behavior described in 4.2.2 On receipt of an IIH with SA bit set the behavior described in 4.2.2
is followed. is followed.
On starting, a router initializes the timer T3, and starts timer T2 On starting, a router starts timer T2 for each LSPDB.
for each LSPDB.
For each interface (and in the case of a LAN circuit, for each For each interface (and in the case of a LAN circuit, for each
level), when an adjacency reaches the UP state, the starting router level), when an adjacency reaches the UP state, the starting router
starts a timer T1 and transmits an IIH containing the restart TLV starts a timer T1 and transmits an IIH containing the restart TLV
with the RR bit clear and SA bit set. On expiry of the timer T1, it with the RR bit clear and SA bit set. On expiry of the timer T1, it
is restarted and the IIH is retransmitted with both RR and SA bits is restarted and the IIH is retransmitted with both RR and SA bits
set(only the RR bit has changed state from earlier IIHs). set(only the RR bit has changed state from earlier IIHs).
On receipt of an IIH with RR bit set(regardless of whether SA is set On receipt of an IIH with RR bit set (regardless of whether SA is
or not) the behavior described in 4.2.1 is followed. set or not) the behavior described in 4.2.1 is followed.
When an IIH is received by the starting router and the IIH contains When an IIH is received by the starting router and the IIH contains
a restart TLV with the RA bit set, the receipt of the a restart TLV with the RA bit set (and on LAN circuits with a
acknowledgement over that interface is noted. Restart Neighbor System ID which matches that of the local system),
the receipt of the acknowledgement over that interface is noted.
T3 is set to the minimum of its current value and the value of the On a Point-to-Point link, receipt of an IIH not containing the
"Remaining Time" field in the received IIH. restart TLV is also treated as an acknowledgement, since it
indicates that the neighbor is not restart capable. Since the
neighbor will have reinitialized the adjacency this guarantees that
SRMflags have been set on its database, thus ensuring eventual LSPDB
synchronization. However, since no CSNP is guaranteed to be received
over this interface, the timer T1 is cancelled immediately without
waiting for a complete set of CSNP(s). Synchronization may therefore
be deemed complete even though there are some LSPs which are held
(only) by this neighbor (see section 4.4).
Receipt of an IIH not containing the restart TLV is also treated as In the case of a LAN interface, receipt of an IIH not containing the
an acknowledgement, since it indicates that the neighbor is not restart TLV is unremarkable since synchronization can still occur so
restart capable. In this case the neighbor will have reinitialized long as at least one of the non-restarting neighboring routers on
the adjacency as normal, which in the case of a Point-to-Point link the LAN supports restart. Therefore T1 continues to run in this
will guarantee that SRMflags have been set on its database, thus case. If none of the neighbors on the LAN are restart capable, T1
ensuring eventual LSPDB synchronization. In the case of a LAN will eventually expire after the locally defined number of retries.
interface, the usual operation of the update process will also The usual operation of the update process will ensure that
ensure that synchronization is eventually achieved. However, since synchronization is eventually achieved.
no CSNP is guaranteed to be received over this interface, T1 is
cancelled immediately without waiting for a CSNP. Synchronization
may therefore be deemed complete even though there are some LSPs
which are held(only) by this neighbor (see section 4.4).
When BOTH a complete set of CSNP(s) (for each active level, in the When BOTH a complete set of CSNP(s) (for each active level, in the
case of a pt-pt circuit) and an acknowledgement have been received case of a pt-pt circuit) and an acknowledgement have been received
over the interface, the timer T1 is cancelled. Subsequent IIHs sent over the interface, the timer T1 is cancelled. Subsequent IIHs sent
by the starting router have the RR and RA bits clear and the SA bit by the starting router have the RR and RA bits clear and the SA bit
set in the restart TLV. set in the restart TLV.
Once T3 has expired or been cancelled, subsequent IIHs are
transmitted according to the normal algorithms, but including the
restart TLV with RR, RA, and SA bits clear.
Timer T1 is cancelled after some pre-determined number of Timer T1 is cancelled after some pre-determined number of
expirations (which MAY be 1). expirations (which MAY be 1).
During the period when T1 is active, according to the rules defined When the T2 timer(s) are cancelled or expire transmission of
in 4.3 the neighbor of the starting router may choose not to update "normal" IIHs (with RR, RA, and SA bits clear) will begin.
the holding time for an adjacency because the RR bit is set in the
received IIH. To prevent holding time expiration a starting router
MAY transmit one or more IIHs containing a restart TLV with RR and
RA bits clear and SA bit set after the initial RR/RA exchange.
When T2 is cancelled or expires transmission of "normal" IIHs (with
RR,RA, and SA bits clear) will begin.
4.3.3 Multiple levels 4.3.3 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.
skipping to change at page 10, line 5 skipping to change at page 11, line 16
When a router is started or restarted it can expect to receive a When a router is started or restarted 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 an IIH with RR bit set will be retransmitted now guaranteed, since an IIH with RR bit set will be retransmitted
until the CSNP(s) are correctly received. 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
been received. been received.
When (re)starting, a router starts the timer T3 and an instance of When (re)starting, a router starts an instance of timer T2 for each
timer T2 for each LSPDB as described in 4.3.1 or 4.3.2. In addition LSPDB as described in 4.3.1 or 4.3.2. In addition to normal
to normal processing of the CSNPs, the set of LSPIDs contained in processing of the CSNPs, the set of LSPIDs contained in the first
the first complete set of CSNP(s) received over each interface is complete set of CSNP(s) received over each interface is recorded,
recorded, together with their remaining lifetime. If there are together with their remaining lifetime. In the case of a LAN
multiple interfaces on the (re)starting router, the recorded set of interface, a complete set of CSNPs MUST consist of CSNPs received
LSPIDs is the union of those received over each interface. LSPs with from neighbor(s) which are not restarting. If there are multiple
a remaining lifetime of zero are NOT so recorded. interfaces on the (re)starting router, the recorded set of LSPIDs is
the union of those received over each interface. LSPs with a
remaining lifetime of zero are NOT so recorded.
As LSPs are received (by the normal operation of the update process) As LSPs are received (by the normal operation of the update process)
over any interface, the corresponding LSPID entry is removed (it is over any interface, the corresponding LSPID entry is removed (it is
also removed if the LSP had arrived before the CSNP containing the also removed if the LSP had arrived before the CSNP containing the
reference). When an LSPID has been held in the list for its reference). When an LSPID has been held in the list for its
indicated remaining lifetime, it is removed from the list. When the indicated remaining lifetime, it is removed from the list. When the
list of LSPIDs is empty and T1 has been cancelled for all the list of LSPIDs is empty and the timer T1 has been cancelled for all
interfaces that have an adjacency at this level, the timer T2 is the interfaces that have an adjacency at this level, the timer T2 is
cancelled. cancelled.
At this point the local database is guaranteed to contain all the At this point the local database is guaranteed to contain all the
LSP(s) (either the same sequence number, or a more recent sequence LSP(s) (either the same sequence number, or a more recent sequence
number) which were present in the neighbors' databases at the time number) which were present in the neighbors' databases at the time
of (re)starting. LSPs that arrived in a neighbor's database after of (re)starting. LSPs that arrived in a neighbor's database after
the time of (re)starting may, or may not, be present, but the normal the time of (re)starting may or may not be present, but the normal
operation of the update process will guarantee that they will operation of the update process will guarantee that they will
eventually be received. At this point the local database is deemed eventually be received. At this point the local database is deemed
to be "synchronized". to be "synchronized".
Since LSPs mentioned in the CSNP(s) with a zero remaining lifetime Since LSPs mentioned in the CSNP(s) with a zero remaining lifetime
are not recorded, and those with a short remaining lifetime are are not recorded, and those with a short remaining lifetime are
deleted from the list when the lifetime expires, cancellation of the deleted from the list when the lifetime expires, cancellation of the
timer T2 will not be prevented by waiting for an LSP that will never timer T2 will not be prevented by waiting for an LSP that will never
arrive. arrive.
skipping to change at page 10, line 52 skipping to change at page 12, line 14
4.4.1.1. Restarting 4.4.1.1. Restarting
In order to avoid causing unnecessary routing churn in other In order to avoid causing unnecessary routing churn in other
routers, it is highly desirable that the own LSPs generated by the routers, it is highly desirable that the own LSPs generated by the
restarting system are the same as those previously present in the restarting system are the same as those previously present in the
network (assuming no other changes have taken place). It is network (assuming no other changes have taken place). It is
important therefore not to regenerate and flood the LSPs until all important therefore not to regenerate and flood the LSPs until all
the adjacencies have been re-established and any information the adjacencies have been re-established and any information
required for propagation into the local LSPs is fully available. required for propagation into the local LSPs is fully available.
Ideally, the information should be loaded into the LSPs in a Ideally, the information is loaded into the LSPs in a deterministic
deterministic way, such that the same information occurs in the same way, such that the same information occurs in the same place in the
place in the same LSP (and hence the LSPs are identical to their same LSP (and hence the LSPs are identical to their previous
previous versions). If this can be achieved, the new versions will versions). If this can be achieved, the new versions will not even
not even cause SPF to be run in other systems. However, provided the cause SPF to be run in other systems. However, provided the same
same information is included in the set of LSPs (albeit in a information is included in the set of LSPs (albeit in a different
different order, and possibly different LSPs), the result of running order, and possibly different LSPs), the result of running the SPF
the SPF will be the same and will not cause churn to the forwarding will be the same and will not cause churn to the forwarding tables.
tables.
In the case of a restarting router, none of the router's LSPs are In the case of a restarting router, none of the router's LSPs are
transmitted, nor are the router's own forwarding tables updated transmitted, nor are the router's own forwarding tables updated
while the timer T3 is running. 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) MUST NOT be flooded until the other level's T2
T2 timer has expired and its SPF has been run. This ensures that any 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 which is to 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
currently have in its own database, it is NOT purged. Under normal currently have in its own database, it is NOT purged. Under normal
operation, such an LSP would be purged, since the LSP clearly should operation, such an LSP would be purged, since the LSP clearly should
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.
During this period a restarting router SHOULD send CSNPs as it During this period a restarting router SHOULD send CSNPs as it
normally would. Information about the router's own LSPs MAY be normally would. Information about the router's own LSPs MAY be
included, but if it is included it MUST be based on LSPs which have included, but if it is included it MUST be based on LSPs which have
been received, not on versions which have been generated(but not yet been received, not on versions which have been generated (but not
transmitted). This restriction is necessary to prevent premature yet transmitted). This restriction is necessary to prevent premature
removal of an LSP from the global LSP database. removal of an LSP from the global LSP database.
When the timer T2 expires or is cancelled indicating that When the timer T2 expires or is cancelled indicating that
synchronization for that level is complete, the SPF for that level synchronization for that level is complete, the SPF for that level
is run in order to derive any information which is required to be is run in order to derive any information which is required to be
propagated to another level, but the forwarding tables are not yet propagated to another level, but the forwarding tables are not yet
updated. 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) MUST 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 When all the T2 timers have expired or been cancelled, the timer T3
is cancelled and the local forwarding tables are updated. is cancelled and the local forwarding tables are updated.
If the timer T3 expires before all the T2 timers have expired or If the timer T3 expires before all the T2 timers have expired or
been cancelled, this indicates that the synchronization process is been cancelled, this indicates that the synchronization process is
taking longer than minimum holding time of the neighbors. The taking longer than minimum holding time of the neighbors. The
router's own LSP(s) for levels which have not yet completed their router's own LSP(s) for levels which have not yet completed their
first SPF computation are then flooded with the overload bit set to first SPF computation are then flooded with the overload bit set to
indicate that the router's LSPDB is not yet synchronized (and other indicate that the router's LSPDB is not yet synchronized (and
routers should therefore not compute routes through this router). therefore other routers MUST NOT compute routes through this
Normal operation of the update process resumes and the local router). Normal operation of the update process resumes and the
forwarding tables are updated. In order to prevent the neighbor's local forwarding tables are updated. In order to prevent the
adjacencies from expiring, IIHs with the normal interface value for neighbor's adjacencies from expiring, IIHs with the normal interface
the holding time are transmitted over all interfaces with neither RR value for the holding time are transmitted over all interfaces with
nor RA set in the restart TLV. This will cause the neighbors to neither RR nor RA set in the restart TLV. This will cause the
refresh their adjacencies. The own LSP(s) will continue to have the neighbors to refresh their adjacencies. The own LSP(s) will continue
overload bit set until timer T2 has expired or been cancelled. to have the overload bit set until timer T2 has expired or been
cancelled.
4.4.1.2. Starting 4.4.1.2. Starting
In the case of a starting router, as soon as each adjacency is In the case of a starting router, as soon as each adjacency is
established, and before any CSNP exchanges, the router's own zeroth established, and before any CSNP exchanges, the router's own zeroth
LSP is transmitted with the overload bit set. This prevents other LSP is transmitted with the overload bit set. This prevents other
routers from computing routes through the router until it has routers from computing routes through the router until it has
reliably acquired the complete set of LSPs. The overload bit remains reliably acquired the complete set of LSPs. The overload bit remains
set in subsequent transmissions of the zeroth LSP (such as will set in subsequent transmissions of the zeroth LSP (such as will
occur if a previous copy of the routers LSP is still present in the occur if a previous copy of the routers LSP is still present in the
skipping to change at page 12, line 50 skipping to change at page 14, line 16
normal. normal.
Other 'own' LSPs (including pseudonodes) are generated and flooded Other 'own' LSPs (including pseudonodes) are generated and flooded
as normal, irrespective of the timer T2. The SPF is also run as as normal, irrespective of the timer T2. The SPF is also run as
normal and the RIB and FIB updated as routes become available. normal and the RIB and FIB updated as routes become available.
To avoid the possible formation of temporary blackholes the starting To avoid the possible formation of temporary blackholes the starting
router sets the SA bit in the restart TLV (as described in 4.3.2) in router sets the SA bit in the restart TLV (as described in 4.3.2) in
all IIHs that it sends. all IIHs that it sends.
When all T2 timers have been cancelled, the starting router MUST When all T2 timers have been cancelled the starting router MUST
transmit IIHs with the SA bit clear. transmit IIHs with the SA bit clear.
5. Security Considerations 5. State Tables
This section presents state tables which summarize the behaviors
described in this document. Other behaviors, in particular adjacency
state transitions and LSP database update operation, are NOT
included in the state tables except where this document modifies the
behaviors described in [3] and [5].
Three state tables are presented from the point of view of a running
router, a restarting router, and a starting router.
5.1 Running Router
Event | Running | ADJ suppressed
==============================================================
RX RR | Maintain ADJ State |
| Send RA |
| Set SRM,send CSNP |
| (Note 1) |
| Update Hold Time, |
| set Restart Mode |
| (Note 2) |
-------------+----------------------+-------------------------
RX RR clr | Clr Restart mode |
-------------+----------------------+-------------------------
RX SA set | Suppress IS neighbor |
| TLV in LSP(s) |
| Goto ADJ Suppressed |
-------------+----------------------+-------------------------
RX SA clr | |Unsuppress IS neighbor
| | TLV in LSP(s)
| |Goto Running
==============================================================
Note 1: If ADJ is UP
Note 2: If Restart Mode clear
5.2 Restarting Router
Event | Restarting | ADJ Seen RA | ADJ Seen CSNP | SPF Wait
===================================================================
Router | Send IIH/RR| | |
restarts | ADJ Init | | |
| Start T1, | | |
| T2,T3 | | |
------------+------------+-------------+---------------+------------
RX RA | Adjust T3 | | Cancel T1 |
| Goto ADJ | | |
| Seen RA | | |
----------- +------------+-------------+---------------+------------
RX CSNP | Goto ADJ | Cancel T1 | |
Set | Seen CSNP| | |
------------+------------+-------------+---------------+------------
RX IIH w/o | Cancel T1 | | |
Restart TLV| | | |
------------+------------+-------------+---------------+------------
T1 Expires | Send IIH/RR| Send IIH/RR | Send IIH/RR |
| Restart T1 | Restart T1 | Restart T1 |
------------+------------+-------------+---------------+------------
T1 Expires | Send IIH/ | Send IIH/ | Send IIH/ |
nth time | normal | normal | normal |
------------+------------+-------------+---------------+------------
T2 expires | Trigger SPF| | |
| Goto SPF | | |
| Wait | | |
------------+------------+-------------+---------------+------------
T3 expires | Set OL | | |
| Flood local| | |
| LSPs | | |
| Update fwd | | |
| plane | | |
------------+------------+-------------+---------------+------------
LSP DB Sync| Cancel T2, | | |
| and T3 | | |
| Trigger SPF| | |
| Goto SPF | | |
| wait | | |
------------+------------+-------------+---------------+------------
All SPF | | | | Clear OL
done | | | | Update Fwd
| | | | plane
| | | | Flood local
| | | | LSPs
| | | | Goto Running
=====================================================================
5.3 Starting Router
Event | Starting | ADJ Seen RA | ADJ Seen CSNP
=========================================================
Router | Send IIH/SA | |
starts | Start T1,T2 | |
-------------+-------------+-------------+---------------
RX RA | Goto ADJ | | Cancel T1
| Seen RA | |
-------------+-------------+-------------+---------------
RX CSNP | Goto ADJ | Cancel T1 |
Set | Seen CSNP | |
-------------+-------------+-------------+---------------
RX IIH w | Cancel T1 | |
no Restart | | |
TLV | | |
-------------+-------------+-------------+---------------
ADJ UP | Start T1 | |
| Send local | |
| LSPs w OL | |
-------------+-------------+-------------+---------------
T1 Expires | Send IIH/RR | Send IIH/RR | Send IIH/RR
| and SA | and SA | and SA
| Restart T1 | Restart T1 | Restart T1
-------------+-------------+-------------+---------------
T1 Expires | Send IIH/SA | Send IIH/SA | Send IIH/SA
nth time | | |
-------------+-------------+-------------+---------------
T2 expires | Clear OL | |
| Send IIH | |
| normal | |
| Goto Running| |
-------------+-------------+-------------+---------------
LSP DB Sync | Cancel T2 | |
| Clear OL | |
| Send IIH | |
| normal | |
=========================================================
6. Security Considerations
This memo does not create any new security issues for the IS-IS This memo does not create any new security issues for the IS-IS
protocol. Security considerations for the base IS-IS protocol are protocol. Security considerations for the base IS-IS protocol are
covered in [2] and [3]. covered in [2] and [3].
6. References 7. References
1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996. 9, RFC 2026, October 1996.
2 Callon, R., "OSI IS-IS for IP and Dual Environment," RFC 1195, 2 Callon, R., "OSI IS-IS for IP and Dual Environment," RFC 1195,
December 1990. December 1990.
3 ISO, "Intermediate system to Intermediate system routeing 3 ISO, "Intermediate system to Intermediate system routeing
information exchange protocol for use in conjunction with the information exchange protocol for use in conjunction with the
Protocol for providing the Connectionless-mode Network Service Protocol for providing the Connectionless-mode Network Service
(ISO 8473)," ISO/IEC 10589:2002, Second Edition. (ISO 8473)," ISO/IEC 10589:2002, Second Edition.
4 Bradner, S., "Key words for use in RFCs to Indicate Requirement 4 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997 Levels", BCP 14, RFC 2119, March 1997
5 Katz, D., "Three-Way Handshake for IS-IS Point-to-Point 5 Katz, D., "Three-Way Handshake for IS-IS Point-to-Point
Adjacencies", RFC 3373, September 2002 Adjacencies", RFC 3373, September 2002
7. Acknowledgments 8. Acknowledgments
The authors would like to acknowledge contributions made by Radia The authors would like to acknowledge contributions made by Jeff
Perlman, Mark Schaefer, Naiming Shen, Nischal Sheth, Russ White, and Parker, Radia Perlman, Mark Schaefer, Naiming Shen, Nischal Sheth,
Rena Yang. Russ White, and Rena Yang.
8. Authors' Addresses 9. Authors' Addresses
Mike Shand Mike Shand
Cisco Systems Cisco Systems
250 Longwater Avenue, 250 Longwater Avenue,
Reading, Reading,
Berkshire, Berkshire,
RG2 6GB RG2 6GB
UK UK
Phone: +44 208 824 8690 Phone: +44 208 824 8690
Email: mshand@cisco.com Email: mshand@cisco.com
 End of changes. 

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