Protocols And Standards - 3Com MSR 50 Series Configuration Manual

Protocols and Standards

Mode-1: It applies to a network where some routers do not support LSP
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fragment extension. In this mode, an 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.
Mode-2: This mode is recommended in a network where all the routers
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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.
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.
A host name is intuitively easier to remember than a system ID. After enabling this
feature on the router, you can see the host names instead of system IDs after using
the display command.
ISO 10589 ISO IS-IS Routing Protocol
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ISO 9542 ES-IS Routing Protocol
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ISO 8348/Ad2 Network Services Access Points
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RFC 1195 - Use of OSI IS-IS for Routing in TCP/IP and Dual Environments
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RFC 2763 - Dynamic Hostname Exchange Mechanism for IS-IS
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RFC 2966 - Domain-wide Prefix Distribution with Two-Level IS-IS
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RFC 2973 - IS-IS Mesh Groups
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RFC 3277 - IS-IS Transient Blackhole Avoidance
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RFC 3358 - Optional Checksums in ISIS
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RFC 3373 - Three-Way Handshake for IS-IS Point-to-Point Adjacencies
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IS-IS Overview 891