Administrator Guide

The following example applies access list Eagle to routes inbound from BGP peer 10.5.5.2. Access list Eagle uses a regular expression to
deny routes originating in AS 32. The rst lines shown in bold create the access list and lter. The second lines shown in bold are the regular
expression shown as part of the access list lter.
Example of Using Regular Expression to Filter AS Paths
DellEMC(config)#router bgp 99
DellEMC(conf-router_bgp)#neigh AAA peer-group
DellEMC(conf-router_bgp)#neigh AAA no shut
DellEMC(conf-router_bgp)#show conf
!
router bgp 99
neighbor AAA peer-group
neighbor AAA no shutdown
neighbor 10.155.15.2 remote-as 32
neighbor 10.155.15.2 shutdown
DellEMC(conf-router_bgp)#neigh 10.155.15.2 filter-list 1 in
DellEMC(conf-router_bgp)#ex
DellEMC(conf)#ip as-path access-list Eagle
DellEMC(config-as-path)#deny 32$
DellEMC(config-as-path)#ex
DellEMC(conf)#router bgp 99
DellEMC(conf-router_bgp)#neighbor AAA filter-list Eagle in
DellEMC(conf-router_bgp)#show conf
!
router bgp 99
neighbor AAA peer-group
neighbor AAA filter-list Eaglein
neighbor AAA no shutdown
neighbor 10.155.15.2 remote-as 32
neighbor 10.155.15.2 filter-list 1 in
neighbor 10.155.15.2 shutdown
DellEMC(conf-router_bgp)#ex
DellEMC(conf)#ex
DellEMC#show ip as-path-access-lists
ip as-path access-list Eagle
deny 32$
DellEMC#
Filtering BGP Routes
Filtering routes allows you to implement BGP policies.
You can use either IP prex lists, route maps, AS-PATH ACLs or IP community lists (using a route map) to control which routes the BGP
neighbor or peer group accepts and advertises. Prex lists lter routes based on route and prex length, while AS-Path ACLs lter routes
based on the ASN. Route maps can lter and set conditions, change attributes, and assign update policies.
NOTE
: Dell EMC Networking OS supports up to 255 characters in a set community statement inside a route map.
NOTE: You can create inbound and outbound policies. Each of the commands used for ltering has in and out parameters that
you must apply. In Dell EMC Networking OS, the order of preference varies depending on whether the attributes are applied for
inbound updates or outbound updates.
For inbound and outbound updates the order of preference is:
• prex lists (using the neighbor distribute-list command)
• AS-PATH ACLs (using the neighbor filter-list command)
• route maps (using the neighbor route-map command)
Prior to ltering BGP routes, create the prex list, AS-PATH ACL, or route map.
For conguration information about prex lists, AS-PATH ACLs, and route maps, refer to Access Control Lists (ACLs).
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Border Gateway Protocol (BGP)