3Com Switch 4800G 24-Port Configuration Manual page 338

338 C 29: IS-IS C
HAPTER
IS-IS Features Supported
n
ONFIGURATION
Code 1 to 10 of CLV are defined in ISO 10589 (code 3 and 5 are not shown in the
table), and others are defined in RFC 1195.
Multiple processes
IS-IS supports multiple processes. Multiple processes allow a IS-IS process to work
in concert with a group of interfaces. This means that a router can run multiple
IS-IS processes, and each process corresponds to a unique group of interfaces.
IS-IS Graceful Restart
For detailed GR information, refer to "GR Overview" on page 247.
After an IS-IS GR Restarter restarts IS-IS, it needs to complete the following two
tasks to synchronize the LSDB with its neighbors.
To obtain effective IS-IS neighbor information without changing adjacencies.
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To obtain the LSDB contents.
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After the restart, the GR Restarter will send an OSPF GR signal to its neighbors to
keep the adjacencies. After receiving the responses from neighbors, the GR
Restarter can restore the neighbor table.
After reestablishing neighbor relationships, the GR Restarter will synchronize the
LSDB and exchange routing information with all adjacent GR capable neighbors.
After that, the GR Restarter will update its own routing table and forwarding table
based on the new routing information and remove the stale routes. In this way,
the IS-IS routing convergence is complete.
Management tag
Management tag carries the management information of the IP address prefixes
and BGP community attribute. It controls the redistribution from other routing
protocols.
LSP fragment extension
IS-IS advertises link state information by flooding LSPs. One LSP carries limited
amount of link state information; therefore, IS-IS fragments LSPs. Each LSP
fragment is uniquely identified by a combination of the System ID, Pseudonode ID
(0 for a common LSP or non-zero for a Pseudonode LSP), and LSP Number (LSP
fragment number) of the node or pseudo node that generated the LSP. The 1-byte
LSP Number field, allowing a maximum of only 256 fragments to be generated by
an IS-IS router, limits the amount of link information that the IS-IS router can
advertise.
The LSP fragment extension feature allows an IS-IS router to generate more LSP
fragments. Each virtual system is capable of generating 256 LSP fragments.
1 Terms
Originating System
■
It is the router actually running IS-IS. After LSP fragment extension is enabled,
additional virtual systems can be configured for the router. Originating system is
the actual IS-IS process that originally runs.