Troubleshooting guide

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

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 <name>

<name> 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 <ipv4 acl name>

<ipv4 acl name> 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.