Understanding Route Filter and Source Address Filter Lists for Use in Routing Policy Match Conditions

Existing route filters and source address filters are configured and processed inline within the term of the policy statement. When route policies are changed, the entire policy is purged and rebuilt during the configuration parsing operation. When this happens on routing policies that include hundreds or even thousands of route filters and source address filters, a significant amount of time is added to the rebuild of the policy.

In order to speed the parsing operation, the route-filter-list and source-address-filter-list statements are available as another means of configuring route filters and source address filters. These statements maintain all the capabilities of the route-filter and source-address-filter statements, including consideration of the prefix length and match type of the individual prefixes in the list.

Route filters and route filter lists are typically used to match an incoming route address to destination match prefixes of any type except for unicast source addresses.

Source address filters and source address filter lists are typically used to match an incoming route address to unicast source addresses in Multiprotocol BGP (MBGP) and Multicast Source Discovery Protocol (MSDP) environments.

Multiple route filter lists and source address filter lists can be used within the same policy statements. Route filter lists and source address filter lists can also be used in conjunction with route filters and source address filters.