H3C S7500E Series Operation Manual page 373

Operation Manual – IPv4 Routing
H3C S7500E Series Ethernet Switches
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.
System ID
The system ID of the originating system.
Additional System ID
It is the additional virtual system ID configured for the IS-IS router after LSP fragment
extension is enabled. Each additional system ID can generate 256 LSP fragments.
Both the additional system ID and the system ID must be unique in the entire routing
domain.
Virtual System
Virtual System is identified by the additional system ID and generates extended LSP
fragments.
Original LSP
It is the LSP generated by the originating system. The system ID in its LSP ID field is the
system ID of the originating system.
Extended LSP
It is the LSP generated by a virtual system. The system ID in its LSP ID field is the
virtual system ID.
After additional system IDs are configured, an IS-IS router can advertise more link state
information in extended LSP fragments. Each virtual system can be considered as a
virtual router. An extended LSP fragment is advertised by a virtual system identified by
additional system ID.
2) Operation modes
The LSP fragment extension feature operates in two modes on an IS-IS router:
Mode-1: It applies to a network where some routers do not support LSP fragment
extension. In this mode, adjacency is formed between the originating system and
each virtual system, with the link cost from the originating system to each virtual
system as 0. Thus, each virtual system acts as a router connected to the
originating system in the network, but the virtual system is reachable through the
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Chapter 4 IS-IS Configuration