Cabletron Systems SmartSwitch Router User's Reference Manual page 92

Chapter 6: BGP Configuration Guide
AS-64901
AS-64900
100.200.12.20/24
100.200.13.1/24
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-list option 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-list option, 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-list option will match any update with any (or no) communities.
92
SSR11
172.25.1.1/16
192.168.20.2/16
192.168.20.1/16
SSR10
Figure 6. Sample BGP Configuration (Well-Known Community)
AS-64902
ISP2
SSR13
172.25.1.2/16
Legend:
Physical Link
Peering Relationship
Information Flow
SmartSwitch Router User Reference Manual
10.220.1.1/16