среда, 8 февраля 2017 г.

What are the different between distribute list, prefix-list and filter-list

The distribute-list and prefix-list perform route filtering based on IP network addresses and netmasks of routes being advertised. The distribute-list refers to an ACL to match the individual networks and netmasks, while prefix-list refers to a prefix list to do this matching. In fact, the use of distribute-list and prefix-list for a particular BGP neighbor in a particular direction (in or out) is mutually exclusive, because they both accomplish the very same goal, just using a different route selection/filtering mechanism (an ACL vs. a prefix list). It is generally better to use prefix lists instead of ACLs - they are much more cleaner and more comprehensible, optimized to match networks/netmasks and subnets thereof.
The filter-list performs route filtering based on the contents of the AS_PATH attribute - the sequence and values of atonomous system numbers. To do this, you would configure an as-path ACL that contains one or more regular expressions matching the particular sequence of ASNs in the AS_PATH attribute, and apply it to a neighbor and a particular direction with the filter-list command. With a filter-list, you do not perform route matching/filtering based on IP addresses and netmasks.

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