Configuring an IPv4 IS-IS Interface to Automatically Adjust the Link Cost

Configuring an IS-IS interface to automatically adjust the link cost based on link quality facilitates route selection control and improves network reliability.

Context

A bit error refers to the deviation between a bit that is sent and the bit that is received. The bit error rate (BER) refers to the number of bit errors divided by the total number of bits transferred during a studied time interval. During data transmission, a high BER may degrade or even interrupt services.

To prevent this problem, configure IS-IS interfaces to automatically adjust link costs based on link quality so that unreliable links are not used by the optimal routes.

Procedure

Run system-view
The system view is displayed.
Run interface interface-type interface-number
The interface view is displayed.
Run isis enable [ process-id ]
IS-IS is enabled on the interface.
Run isis link-quality low incr-cost { cost-value | max-reachable }
The IS-IS interface is configured to automatically adjust the link cost based on link quality.
The cost parameter specifies the link cost adjustment value. After this parameter is specified:
- If the link quality changes from good to low, the link cost equals the original link cost plus the adjustment value. If the new link cost exceeds the maximum link cost allowed, the maximum link cost allowed applies:
  The maximum link cost is 63, if the cost style is narrow, narrow-compatible, or compatible.
  The maximum link cost is 16777214, if the cost style is wide or wide-compatible.
- If the link quality changes from low to good, the original link cost applies.
Run commit
The configuration is committed.