Riverstone Networks WICT1-12 - Manual (Page 282)

16-24 Riverstone Networks RS Switch Router User Guide Release 8.0
BGP Configuration Examples BGP Configuration Guide
Figure 16-6 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-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.
AS-64902
Physical Link
Legend:
Peering Relationship
R
11
Information Flow
172.25.1.2/16
192.168.20.2/16
172.25.1.1/16
R
13
R
10
192.168.20.1/16
100.200.13.1/24
AS-64901
AS-64900
ISP2
100.200.12.20/24
ISP1
CS1
10.220.1.1/16