Troubleshooting guide

Additional BGP Configuration

Defining Routes and Attributes to Advertise Outbound or Filter Inbound

The advertisements sent from a BGP interface to a neighbor or received by a BGP interface from a

neighbor can be controlled according to the route’s:

• IPv4 Network address and prefix length

•AS path

• Community

•Metric

Routes that the BGP interface will advertise outbound or filter inbound are sel

ected by entering a match

command in a route map entry. The difference between an inbound filter and an outbound filter is seen

when the route map is applied to a BGP neighbor as an inbound policy rather than an outbound policy.

Refer to Applying a Route Map Entry to a BGP Neighbor on page 30. For a list of available filtering

options for BGP, see Table 3 on page 24.

Table 3. Defining Routes to Be Filtered

IPv4 Network address and/or prefix

length

match ip address prefix-list <name>

IPv4 ACL match ip address <ipv4 acl na

me>

AS_PATH match as-path <n

ame>

Community match community <nam

e> exact-match

Metric match metric <v

alue>

Detailed explanations of the above match commands begin with Filtering Routes According to Network

IPv4 Address on page 25.

After creating a route map, route map attributes can be defined from the Route Map

Configuration mode. Enter ? at the (config-route-map)# prompt to explore the available

options.

Filtering According To Command Syntax

If a BGP route does not contain a qualifying prefix or attribute that matches any of the

filters specified in the route map or if a BGP route matches a deny route map entry, then the

route will not be allowed in or out.

If the only action required is filtering of routes, then the match command is entered and the

route map is applied to the BGP neighbor as either an outbound or inbound policy (refer to

Applying a Route Map Entry to a BGP Neighbor on page 30).