IS-IS Wide Metric

In ISO 10589, the maximum IS-IS interface metric value can only be 63 and the IS-IS cost style is narrow. A small range of metrics cannot meet the requirements on large-scale networks. Therefore, in RFC 3784, the maximum IS-IS interface metric value can reach 16777215, and the maximum IS-IS route metric value can reach 4261412864; in this case, the IS-IS cost style is wide.

The following lists the TLVs used in narrow mode:
- TLV 128 (IP Internal Reachability TLV): carries IS-IS routes in a routing domain.
- TLV 130 (IP External Reachability TLV): carries IS-IS routes outside a routing domain.
- TLV 2 (IS Neighbors TLV): carries neighbor information.
The following lists the TLVs used in wide mode:
- TLV 135 (Extended IP Reachability TLV): replaces the earlier IP reachability TLV and carries IS-IS routing information. This TLV expands the route metric and carries sub-TLVs.
- TLV 22 (IS Extended Neighbors TLV): carries neighbor information.

Table 1 lists the cost styles of received and sent IS-IS routing information. The cost styles of received and sent IS-IS routing information vary according to the cost style configured on a device.

**Table 1** Cost styles of received and sent IS-IS routing information
Cost Style Configured on a Device	Cost Style for Received IS-IS Routing Information	Cost Style for Sent IS-IS Routing Information
narrow	narrow	narrow
narrow-compatible	narrow&wide	narrow
compatible	narrow&wide	narrow&wide
wide-compatible	narrow&wide	wide
wide	wide	wide

When the cost-style is set to compatible, IS-IS sends the information in narrow mode and in wide mode respectively.

IS-IS in wide mode and IS-IS in narrow mode cannot communicate. If IS-IS in wide mode and IS-IS in narrow mode need to communicate, you must change the mode to enable all routers on the network to receive packets sent by other routers.