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Extensions for Traffic Engineering

The router supports new-style TLV tuples described in the Internet draft, IS-IS Extensions for Traffic Engineering. The router ID TLV (TLV type 134) contains the ID of the router that originates the LSP, providing a stable address that can always be referenced regardless of the state of node interfaces.

The extended IP reachability TLV (type 135) carries IP prefixes and is similar to the IP reachability TLVs (types 128 and 130). The extended IS reachability TLV (type 22) contains information about a series of IS neighbors and is similar to the IS neighbor TLV (type 2).

The older TLVs—2, 128, 130—each have a narrow metric field, providing for metric values ranging only from 0–63. The new TLVs—22 and 135—have a new data structure that includes a wide metric field of 3 bytes (extended IS reachability; configurable) or four bytes (extended IP reachability; calculated). Both new TLVs provide for the use of sub-TLVs to carry more information about IS neighbors; however, only the extended IS reachability TLV currently has defined sub-TLVs, such as IPv4 interface and neighbor addresses.

Use the metric-style commands to configure what style the router generates and accepts. The following behaviors are supported:

Generates and accepts only old-style metrics
Generates only old-style metrics, but accepts old style and new style
Generates and accepts both old-style and new-style metrics (this option consumes the most system resources)
Generates only new-style metrics, but accepts old style and new style
Generates and accepts only new-style metrics

Refer to the Internet draft, IS-IS Extensions for Traffic Engineering, for more information about these extensions.

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