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Additional BGP Configuration
If an attribute is to be applied to the route, then a set command must be entered in addition to the match
command. Attributes are applied to the routes selected by the match command. The following attributes
can be applied to inbound filtered or outbound advertised routes:
• Community
• Prepend AS path
• MED metric
• Local preference
• Delete a community list
Detailed explanations of the set command attributes begin with Prepending Private AS Numbers for Load
Balancing on page 28.
Filtering Routes According to Network IPv4 Address
One way to use route maps to filter routes is according to the IPv4 network address and/or prefix
length. A prefix list is first created to define the routes that are to be filtered by the BGP interface (refer
to Prefix List on page 21). The prefix list delineates either routes that the BGP interface will advertise
outbound or inbound routes that should be filtered. An exact route can be specified or a range of prefix
lengths for routes to variable length subnets. After the prefix list has been configured, it is referenced
in a route map entry. The route map entry is then applied to a BGP neighbor (refer to Applying a Route
Map Entry to a BGP Neighbor on page 30).
Use the match ip address prefix-list command to configure the route map to route traffic based on a
prefix list route filter:
(config-route-map)#match ip address prefix-list
Specifies the name of the prefix list.
Another way to use route maps to filter routes according to network address is by using standard or
extended IPv4 ACLs. As with prefix lists, an ACL is first created to define the routes that are to be
filtered by the BGP interface. Refer to IP ACLs in AOS (ADTRAN’s Knowledge Base article 3087) for
information on how to create a standard or extended IPv4 ACL. After the ACL has been configured, it
is referenced in a route map entry (see below) or applied to a BGP neighbor using the distribute-list
command (refer to Distribute List on page 17). The route map entry is then applied to a BGP neighbor
(refer to Applying a Route Map Entry to a BGP Neighbor on page 30).
Use the match ip address command to configure the route map to process traffic based on the ACL
name defined with the ip access-list command:
(config-route-map)#match ip address
Specifies the name of the IPv4 ACL to match.
Use set commands to configure any attributes (prepend AS_PATH,
MULTI_EXIT_DISC, LOCAL_PREF, etc.) to be applied to the routes prior to
associating the route map with the BGP neighbor. Refer to Prepending Private AS
Numbers for Load Balancing on page 28 for detailed explanations of the set command
attributes.
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