Concept Guide

3 Return to CONFIGURATION mode.
AS-PATH ACL
exit
4 Enter ROUTER BGP mode.
CONFIGURATION mode
router bgp as-number
5 Filter routes based on the criteria in the congured route map.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | ipv6-address | peer-group-name} filter-list as-path-name {in | out}
Congure the following parameters:
• ip-address or ip-address or peer-group-name: enter the neighbor’s IPv4 or IPv6 address or the peer group’s name.
• as-path-name: enter the name of a congured AS-PATH ACL.
• in: apply the AS-PATH ACL map to inbound routes.
• out: apply the AS-PATH ACL to outbound routes.
Example conguration for ltering BGP routes using AS-PATH information
Following is the sample conguration for ltering BGP routes using AS-PATH information
DellEMC# configure terminal
DellEMC(conf)# ip as-path access-list 100 deny ^500$
DellEMC(conf)# ip as-path access-list 100 permit .*
DellEMC(conf)# router bgp 400
DellEMC(conf_router_bgp)# neighbor 10.10.10.1 remote-as 450
DellEMC(conf_router_bgp_af)# address-family ipv4 multicast
DellEMC(conf_router_bgp_af)# neighbor 10.10.10.2 filter-list 100 out
DellEMC(conf_router_bgp_af)# exit
In the above example, a BGP access list (100) is dened to deny any AS-path that starts and ends with 500 and permit all other routes.
The access list is applied for outgoing BGP routes for the neighbor (10.10.10.2) and the routes are ltered or distributed based on the
congured rules set in the access list.
To view which commands are congured, use the show config command in CONFIGURATION ROUTER BGP mode and the show ip
as-path-access-list command in EXEC Privilege mode.
To forward all routes not meeting the AS-PATH ACL criteria, include the permit .* lter in your AS-PATH ACL.
Conguring Peer Groups
To congure a peer group, use the following commands.
1 Enter the router conguration mode and the AS number.
CONFIG mode
router bgp as-number
2 Create a peer group by assigning a name to it.
CONFIG-ROUTER-BGP mode
neighbor peer-group-name peer-group
3 Enable the peer group.
CONFIG-ROUTER-BGP mode
neighbor peer-group-name no shutdown
200
Border Gateway Protocol (BGP)