Cabletron Systems SmartSwitch manual Sample BGP Configuration Well-Known Community

Chapter 10: BGP Configuration Guide

AS-64901 AS-64902

AS-64900

100.200.12.20/24

100.200.13.1/24

SSR11

172.25.1.1/16

192.168.20.2/16

192.168.20.1/16

SSR10

172.25.1.2/16

Legend:

ISP2

SSR13

10.220.1.1/16

Physical Link

Peering Relationship

Information Flow

Figure 12. Sample BGP Configuration (Well-Known Community)

The Community attribute can be used in three ways:

1.In a BGP Group statement: Any packets sent to this group of BGP peers will have the communities attribute in the BGP packet modified to be this communities attribute value from this AS.

2.In an Import Statement: Any packets received from a BGP peer will be checked for the community attribute. The optional-attributes-listoption of the ip-router policy create command allows the specification of an import policy based on optional path attributes (for instance, the community attribute) found in the BGP update. If multiple communities are specified in the optional-attributes-listoption, only updates carrying all of the specified communities will be matched. If well-known-community none is specified, only updates lacking the community attribute will be matched.

Note that it is quite possible for several BGP import clauses to match a given update. If more than one clause matches, the first matching clause will be used; all later matching clauses will be ignored. For this reason, it is generally desirable to order import clauses from most to least specific. An import clause without an optional- attributes-listoption will match any update with any (or no) communities.

SmartSwitch Router User Reference Manual 149