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140 CHAPTER 5: IP ROUTING PROTOCOL OPERATION
By default, MED comparison is not allowed among routes from neighbors in
different ASs.
You should not use this configuration unless you can make sure that the ASs
adopt the same IGP routing method.
Configuring BGP Community
Community attributes are optional and transitive. Some community attributes are
globally recognized, which are called standard community attributes, whereas
some are for special purposes which are called extended community attributes.
You may define not only the standard community, but also the extended
community attributes.
Community-list is used to identify a community, which falls into standard
community-list and extended community-list.
In addition, a route can have more than one community attribute. In a route, the
speaker of multiple community attributes can act according to one, several, or all
of the attributes. A router can choose to change the community attribute or leave
it unchanged before transmitting the route to its peers.
Perform the following configurations in system view..
By default, no BGP community is configured.
Configuring a BGP Route Reflector
To ensure the interconnection between IBGP peers, it is necessary to establish a
fully meshed network. In some networks, there are large numbers of IBGP peers so
the cost to establish a fully meshed network is large. Thus, it is necessary to
configure a route reflector which specifies a centralized router as the focus of the
internal session.
The route reflector is the centralized point for other routers, called clients. The
client is the peer of the route reflector and exchanges routing information with it.
The route reflector reflects information among the clients. A single route reflector
can have multiple clients. Each client, in turn, can be a route reflector with
multiple clients.
Table 122 Configuring Community
Operation Command
Configure a standard community list ip community-list
standard-community-list-number { permit |
deny } { aa:nn | internet |
no-export-subconfed | no-advertise |
no-export }
Configure an extended community list ip community-list
extended-community-list-number { permit |
deny } as-regular-expression
Remove the configured community list undo ip community-list {
standard-community-list-number |
extended-community-list-number }