Concept Guide

NOTE: With the Dell Networking OS, you can create inbound and outbound policies. Each of the commands used for ltering has
in and out parameters that you must apply. In the system, 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).
NOTE: When you congure a new set of BGP policies, to ensure the changes are made, always reset the neighbor or peer group
by using the clear ip bgp command in EXEC Privilege mode.
To lter routes using prex lists, use the following commands.
1 Create a prex list and assign it a name.
CONFIGURATION mode
ip prefix-list prefix-name
2 Create multiple prex list lters with a deny or permit action.
CONFIG-PREFIX LIST mode
seq sequence-number {deny | permit} {any | ip-prefix [ge | le] }
• ge: minimum prex length to be matched.
• le: maximum prex length to be matched.
For information about conguring prex lists, refer to Access Control Lists (ACLs).
3 Return to CONFIGURATION mode.
CONFIG-PREFIX LIST mode
exit
4 Enter ROUTER BGP mode.
CONFIGURATION mode
router bgp as-number
5 Filter routes based on the criteria in the congured prex list.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | peer-group-name} distribute-list prefix-list-name {in | out}
Congure the following parameters:
• ip-address or peer-group-name: enter the neighbor’s IP address or the peer group’s name.
• prefix-list-name: enter the name of a congured prex list.
• in: apply the prex list to inbound routes.
• out: apply the prex list to outbound routes.
As a reminder, the following are rules concerning prex lists:
• If the prex list contains no lters, all routes are permitted.
• If none of the routes match any of the lters in the prex list, the route is denied. This action is called an implicit deny. (If you want to
forward all routes that do not match the prex list criteria, you must congure a prex list lter to permit all routes. For example, you
could have the following lter as the last lter in your prex list permit 0.0.0.0/0 le 32).
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Border Gateway Protocol IPv4 (BGPv4)