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Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 29 Configuring IP Unicast Routing
Configuring BGP
Use the no neighbor distribute-list command to remove the access list from the neighbor. Use the no
neighbor route-map map-tag router configuration command to remove the route map from the
neighbor.
Another method of filtering is to specify an access list filter on both incoming and outbound updates,
based on the BGP autonomous system paths. Each filter is an access list based on regular expressions.
(See the “Regular Expressions” appendix in the Cisco IOS Dial Technologies Command Reference,
Release 12.2 for more information on forming regular expressions.) To use this method, define an
autonomous system path access list, and apply it to updates to and from particular neighbors.
Beginning in privileged EXEC mode, follow these steps to configure BGP path filtering:
Configuring Prefix Lists for BGP Filtering
You can use prefix lists as an alternative to access lists in many BGP route filtering commands, including
the neighbor distribute-list router configuration command. Filtering by a prefix list involves matching
the prefixes of routes with those listed in the prefix list, as when matching access lists. When there is a
match, the route is used. Whether a prefix is permitted or denied is based upon these rules:
•
An empty prefix list permits all prefixes.
•
An implicit deny is assumed if a given prefix does not match any entries in a prefix list.
Step 3
neighbor {ip-address | peer-group name}
distribute-list {access-list-number | name}
{in | out}
(Optional) Filter BGP routing updates to or from neighbors as
specified in an access list.
Note
You can also use the neighbor prefix-list router
configuration command to filter updates, but you cannot use
both commands to configure the same BGP peer.
Step 4
neighbor {ip-address | peer-group name}
route-map map-tag {in | out}
(Optional) Apply a route map to filter an incoming or outgoing
route.
Step 5
end
Return to privileged EXEC mode.
Step 6
show ip bgp neighbors
Verify the configuration.
Step 7
copy running-config startup-config
(Optional) Save your entries in the configuration file.
Command
Purpose
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
ip as-path access-list access-list-number
{permit | deny} as-regular-expressions
Define a BGP-related access list.
Step 3
router bgp autonomous-system
Enter BGP router configuration mode.
Step 4
neighbor {ip-address | peer-group name}
filter-list {access-list-number | name} {in |
out | weight weight}
Establish a BGP filter based on an access list.
Step 5
end
Return to privileged EXEC mode.
Step 6
show ip bgp neighbors [paths
regular-expression]
Verify the configuration.
Step 7
copy running-config startup-config
(Optional) Save your entries in the configuration file.
