draft-ietf-lsr-isis-rfc5306bis-06.txt   draft-ietf-lsr-isis-rfc5306bis-07.txt 
IS-IS for IP Internets L. Ginsberg IS-IS for IP Internets L. Ginsberg
Internet-Draft P. Wells Internet-Draft P. Wells
Obsoletes: 5306 (if approved) Cisco Systems, Inc. Obsoletes: 5306 (if approved) Cisco Systems, Inc.
Intended status: Standards Track September 18, 2019 Intended status: Standards Track September 18, 2019
Expires: March 21, 2020 Expires: March 21, 2020
Restart Signaling for IS-IS Restart Signaling for IS-IS
draft-ietf-lsr-isis-rfc5306bis-06 draft-ietf-lsr-isis-rfc5306bis-07
Abstract Abstract
This document describes a mechanism for a restarting router to signal This document describes a mechanism for a restarting router to signal
to its neighbors that it is restarting, allowing them to reestablish to its neighbors that it is restarting, allowing them to reestablish
their adjacencies without cycling through the down state, while still their adjacencies without cycling through the down state, while still
correctly initiating database synchronization. correctly initiating database synchronization.
This document additionally describes a mechanism for a router to This document additionally describes a mechanism for a router to
signal its neighbors that it is preparing to initiate a restart while signal its neighbors that it is preparing to initiate a restart while
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The terms "normal IIH" or "IIH normal" refer to IS-IS Hellos (IIHs) The terms "normal IIH" or "IIH normal" refer to IS-IS Hellos (IIHs)
in which the Restart TLV (defined later in this document) has no in which the Restart TLV (defined later in this document) has no
flags set. flags set.
3. Approach 3. Approach
3.1. Timers 3.1. 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
behavior of a restarting router defined in this document. mechanisms defined in this document. Timers T1 and T2 are used both
by a restarting router and a starting router. Timer T3 is used only
by a restarting router.
NOTE: These timers are NOT applicable to a router which is preparing NOTE: These timers are NOT applicable to a router which is preparing
to do a planned restart. to do a planned restart.
An instance of the timer T1 is maintained per interface, and An instance of the timer T1 is maintained per interface, and
indicates the time after which an unacknowledged (re)start attempt indicates the time after which an unacknowledged (re)start attempt
will be repeated. A typical value is 3 seconds. will be repeated. A typical value is 3 seconds.
An instance of the timer T2 is maintained for each LSP database An instance of the timer T2 is maintained for each LSP database
(LSPDB) present in the system. For example, for a Level 1/2 system, (LSPDB) present in the system. For example, for a Level 1/2 system,
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A single instance of the timer T3 is maintained for the entire A single instance of the timer T3 is maintained for the entire
system. It indicates the time after which the router will declare system. It indicates the time after which the router will declare
that it has failed to achieve database synchronization (by setting that it has failed to achieve database synchronization (by setting
the overload bit in its own LSP). This is initialized to 65535 the overload bit in its own LSP). This is initialized to 65535
seconds, but is set to the minimum of the remaining times of received seconds, but is set to the minimum of the remaining times of received
IIHs containing a restart TLV with the Restart Acknowledgement (RA) IIHs containing a restart TLV with the Restart Acknowledgement (RA)
set and an indication that the neighbor has an adjacency in the "UP" set and an indication that the neighbor has an adjacency in the "UP"
state to the restarting router. (See Section 3.2.1a.) state to the restarting router. (See Section 3.2.1a.)
NOTE: The timer T3 is only used by a restarting router.
3.2. Restart TLV 3.2. 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 defined this TLV indicates that the sender supports the functionality defined
in this document. The TLV includes flags that are used to convey in this document. The TLV includes flags that are used to convey
information during a (re)start. All IIHs transmitted by a router information during a (re)start. All IIHs transmitted by a router
that supports this capability MUST include this TLV. that supports this capability MUST include this TLV.
Type 211 Type 211
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+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+
RR - Restart Request RR - Restart Request
RA - Restart Acknowledgement RA - Restart Acknowledgement
SA - Suppress adjacency advertisement SA - Suppress adjacency advertisement
PR - Restart is planned PR - Restart is planned
PA - Planned restart acknowledgement PA - Planned restart acknowledgement
Remaining Time (2 octets) Remaining Time (2 octets)
Remaining/recommended holding time (in seconds). Remaining holding time (in seconds).
Required when the RA, PR, or PA bit is set. Otherwise Required when the RA, PR, or PA bit is set. Otherwise
this field SHOULD be omitted when sent and this field SHOULD be omitted when sent and
MUST be ignored when received. MUST be ignored when received.
Restarting Neighbor System ID (ID Length octets) Restarting Neighbor System ID (ID Length octets)
The System ID of the neighbor to which an RA/PA refers. The System ID of the neighbor to which an RA/PA refers.
Required when the RA or PA bit is set. Otherwise Required when the RA or PA bit is set. Otherwise
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clear, or the adjacency holding time expires - whichever occurs clear, or the adjacency holding time expires - whichever occurs
first. first.
While the adjacency is in planned restart state some or all of the While the adjacency is in planned restart state some or all of the
following actions MAY be taken: following actions MAY be taken:
a. if additional topology changes occur, the adjacency which is in a. if additional topology changes occur, the adjacency which is in
planned restart state MAY be brought down even though the hold planned restart state MAY be brought down even though the hold
time has not yet expired. Given that the neighbor which has time has not yet expired. Given that the neighbor which has
signaled a planned restart is not expected to update its signaled a planned restart is not expected to update its
forwarding plane in response to signaling of the topology changes forwarding plane in response to signalling of the topology
(since it is restarting) traffic which transits that node is at changes (since it is restarting) traffic which transits that node
risk of being improperly forwarded. On a LAN circuit, if the is at risk of being improperly forwarded. On a LAN circuit, if
router in planned restart state is the DIS at any supported the router in planned restart state is the DIS at any supported
level, the adjacency(ies) SHOULD be brought down whenever any LSP level, the adjacency(ies) SHOULD be brought down whenever any LSP
update is either generated or received, so as to trigger a new update is either generated or received, so as to trigger a new
DIS election. Failure to do so will compromise the reliability DIS election. Failure to do so will compromise the reliability
of the Update Process on that circuit. What other criteria are of the Update Process on that circuit. What other criteria are
used to determine what topology changes will trigger bringing the used to determine what topology changes will trigger bringing the
adjacency down is a local implementation decision. adjacency down is a local implementation decision.
b. if a BFD [RFC5880] session to the neighbor which signals a b. if a BFD [RFC5880] session to the neighbor which signals a
planned restart is in the UP state and subsequently goes DOWN, planned restart is in the UP state and subsequently goes DOWN,
the event MAY be ignored since it is possible this is an expected the event MAY be ignored since it is possible this is an expected
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