IS-IS Wide Metric
A small range of metrics cannot meet the requirements of large-scale networks.
In the earlier ISO 10589, the greatest value of an interface metric was only 63. TLV type 128 and TLV type 130 contained information about routes; TLV type 2 contained information about IS-IS neighbors.
The following TLVs are used in narrow mode:
IP Internal Reachability: carries internal routes.
IP External Reachability: carries external routes.
IS Neighbors: carries information about neighbors.
The following TLVs are used in wide mode:
Extended IP Reachability: replaces the earlier IP reachability TLV and carries information about routes. This TLV expands the range of route cost to 4 bytes and carries sub-TLVs.
IS Extended Neighbors: carries information about neighbors.
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.
Mode\Receiving and Sending |
Receiving |
Sending |
|---|---|---|
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 then in wide mode.
Changing the sending mode from narrow to wide
The information that used to be carried by TLV type 128, TLV type 130, and TLV type 2 is now carried by TLV type 135 and TLV type 22.
Changing the sending mode from wide to narrow
The information that used to be carried by TLV type 135 and TLV type 22 is now carried by TLV type 128, TLV type 130, and TLV type 2.
Changing the sending mode from narrow/wide to narrow&wide
The information that used to be carried in narrow/wide mode is now carried by TLV type 128, TLV type 130, TLV type 2, TLV type 135, and TLV type 22.