IS-IS Accept Policy Considerations

Consider the following when you configure IS-IS accept policies:

Precedence rules in the same VSN

The following precedence rules apply for IS-IS accept policies used in the same VSN:
  • You can only apply one configured IS-IS accept policy for each route.

  • You can apply either a default filter for all advertising BEBs or a filter for a specific advertising BEB.

  • If you disable the accept filter, the system ignores the filter and the filter with the next highest precedence applies.

  • The device prefers the accept adv-rtr filter, which filters based on a specific advertising BEB, over the default filter for all advertising BEBs.

  • The device accepts all routes within the same VSN by default. You can apply a route policy to filter or change the characteristics of the route by metric or preference.

  • The i-sid or isid-list filters are not valid for routes within the same VSN.

Precedence rules for inter-VSN route redistribution

The following precedence rules apply for IS-IS accept policies used for inter-VSN route redistribution:
  • You can only apply one configured IS-IS accept policy for each route.

  • You can apply filters at a global default level for all BEBs for a specific I-SID or I-SID list, or you can apply filters for a specific advertising BEB for a specific I-SID or I-SID list.

  • If you disable the accept filter, the system ignores the filter and the filter with the next highest precedence applies.

  • The device requires a specific filter to redistribute routes between VSNs through the use of the i-sid or isid-list filters.

  • The i-sid filter takes precedence over the isid-list filter.

  • The adv-rtr filter for a specific advertising BEB takes precedence over a filter with the same i-sid filter without the adv-rtr filter.

  • The i-sid or isid-list filters only apply to routes for inter-VSN route redistribution.

  • If multiple isid-list filters have the same I-SID within the list, the first on the list alphabetically has the higher precedence.