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Introduction
Page 2 | Use Route Maps and Other Filters to Filter and Alter BGP and OSPF Routes
Contents
Introduction ..................................................................................................................................................................................................................1
Related How To Notes................................................................................................................................................................................3
Which products and software version does it apply to?..........................................................................................................3
BGP: Concepts and Terminology.....................................................................................................................................................................4
BGP peers ...........................................................................................................................................................................................................4
BGP updates.......................................................................................................................................................................................................4
Update attributes............................................................................................................................................................................................5
BGP: Overview of the Available Filter Types.............................................................................................................................................6
Filter types ...........................................................................................................................................................................................................6
Hierarchy of the Different Filters.....................................................................................................................................................................8
BGP: Example....................................................................................................................................................................................................8
Basic configuration..........................................................................................................................................................................................9
BGP: Configuring Distribute Filters ..............................................................................................................................................................11
About ACLs..................................................................................................................................................................................................... 11
Using ACLs as filters...................................................................................................................................................................................12
Example: Distribute filters .......................................................................................................................................................................12
BGP: Configuring AS Path Filters...................................................................................................................................................................17
AS path lists.....................................................................................................................................................................................................17
Using AS path lists as path filters.........................................................................................................................................................18
Example: AS path filters............................................................................................................................................................................18
BGP: Configuring Prefix Filters........................................................................................................................................................................22
About prefix lists...........................................................................................................................................................................................22
Mask length......................................................................................................................................................................................................22
Using prefix lists as prefix filters...........................................................................................................................................................23
Example: Prefix filters.................................................................................................................................................................................23
BGP: Configuring Route Maps........................................................................................................................................................................26
Structure of a route map.........................................................................................................................................................................26
Clauses................................................................................................................................................................................................................27
Configuring a match clause..................................................................................................................................................................... 27
Configuring a set clause............................................................................................................................................................................30
The effect of different combinations of clauses..........................................................................................................................33
BGP: Applying Distribute, Path, Prefix, and Route Map Filters to a Peer..............................................................................35
Examples......................................................................................................................................................................................................................36
BGP: Applying Route Maps to Imported Routes.................................................................................................................................46
Syntax..................................................................................................................................................................................................................46
Other Uses of Route Maps ..............................................................................................................................................................................47
neighbor default-originate .......................................................................................................................................................................47
neighbor unsuppress-map.......................................................................................................................................................................47
network..............................................................................................................................................................................................................47
show ip bgp.....................................................................................................................................................................................................47