
Operation Manual – IPv4 Routing
H3C S3610&S5510 Series Ethernet Switches
Chapter 4 IS-IS Configuration
4-17
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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:
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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
originating system only. Therefore, the IS-IS routers not supporting LSP fragment
extension can operate normally without modifying the extended LSP fragments
received, but some limitation is imposed on the link state information in the
extended LSP fragments advertised by the virtual systems.
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Mode-2: This mode is recommended in a network where all the routers support
LSP fragment extension. In this mode, all the IS-IS routers in the network know
which originating system the LSPs generated by the virtual systems belong to;
therefore no limitation is imposed on the link state information of the extended LSP
fragments advertised by the virtual systems.
The operation mode of LSP fragment extension is configured based on area and
routing level. Mode-1 is backward-compatible and allows the routers supporting LSP
fragment extension and those not supporting this feature to interoperate with each
other, but it restricts the link state information in the extended fragments. Mode-2 does
not restrict the link state information in the extended fragments. Mode-2 is
recommended in a network where all the routers that are in the same area and at the
same routing level support LSP fragment extension.
V. Dynamic host name mapping mechanism
The dynamic host name mapping mechanism provides the mapping between the host
names and the system IDs for the IS-IS routers. The dynamic host name information is
announced in the dynamic host name CLV of an LSP.
This mechanism also provides the mapping between a host name and the DIS of a
broadcast network, which is announced in a dynamic host name TLV of a pseudonode
LSP.