Administrator Guide

NOTE: You can create inbound and outbound policies. Each of the commands used for filtering 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:
● prefix 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 filtering BGP routes, create the prefix list, AS-PATH ACL, or route map.
For configuration information about prefix lists, AS-PATH ACLs, and route maps, refer to Access Control Lists (ACLs).
NOTE: When you configure 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.
Filtering BGP using IP prefix lists
An IP prefix lists contains a list of networks. When applying an IP prefix list to a BGP neighbor, you can able to send or receive
the routes whose destination is in the IP prefix list.
Filtering BGP routes based on IP prefix lists involves the following steps:
● Create a prefix list. The steps 1 to 3 in the following configuration commands shows how to create a prefix list.
● Applying the created prefix list to a BGP neighbor. The steps 4 and 5 show how the prefix list is applied to a neighbor.
To configure an IP prefix list, use the following commands.
1. Create a prefix list and assign it a name.
CONFIGURATION mode
ip prefix-list prefix-name
2. Create multiple prefix list filters with a deny or permit action.
CONFIG-PREFIX LIST mode
seq sequence-number {deny | permit} {any | ip-prefix [ge | le] }
● ge: minimum prefix length to be matched.
● le: maximum prefix length to me matched.
For information about configuring prefix 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 configured prefix list.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | ipv6-address | peer-group-name} distribute-list prefix-list-name
{in | out}
Configure the following parameters:
● ip-address or ipv6-address or peer-group-name: enter the neighbor’s IPv4 or IPv6 address or the peer group’s
name.
● prefix-list-name: enter the name of a configured prefix list.
● in: apply the prefix list to inbound routes.
● out: apply the prefix list to outbound routes.
As a reminder, the following are rules concerning prefix lists:
● If the prefix list contains no filters, all routes are permitted.
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Border Gateway Protocol (BGP)