User's Manual

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