Reference Guide

Implementation Information
Prefix lists are used in processing routes for routing protocols (for example, router information protocol [RIP], open shortest
path first [OSPF], and border gateway protocol [BGP]).
NOTE: It is important to know which protocol your system supports prior to implementing prefix-lists.
Configuration Task List for Prefix Lists
To configure a prefix list, use commands in PREFIX LIST, ROUTER RIP, ROUTER OSPF, and ROUTER BGP modes.
Create the prefix list in PREFIX LIST mode and assign that list to commands in ROUTER RIP, ROUTER OSPF and ROUTER BGP
modes.
The following list includes the configuration tasks for prefix lists, as described in the following sections.
● Configuring a prefix list
● Use a prefix list for route redistribution
For a complete listing of all commands related to prefix lists, refer to the Dell Networking OS Command Line Reference Guide.
Creating a Prefix List
To create a prefix list, use the following commands.
1. Create a prefix list and assign it a unique name.
You are in PREFIX LIST mode.
CONFIGURATION mode
ip prefix-list prefix-name
2. Create a prefix list with a sequence number and a deny or permit action.
CONFIG-NPREFIXL mode
seq sequence-number {deny | permit} ip-prefix [ge min-prefix-length] [le max-prefix-
length]
The optional parameters are:
● ge min-prefix-length: the minimum prefix length to match (from 0 to 32).
● le max-prefix-length: the maximum prefix length to match (from 0 to 32).
If you want to forward all routes that do not match the prefix list criteria, configure a prefix list filter to permit all routes
(permit 0.0.0.0/0 le 32). The “permit all” filter must be the last filter in your prefix list. To permit the default route only,
enter permit 0.0.0.0/0.
The following example shows how the seq command orders the filters according to the sequence number assigned. In the
example, filter 20 was configured before filter 15 and 12, but the show config command displays the filters in the correct
order.
Dell(conf-nprefixl)#seq 20 permit 0.0.0.0/0 le 32
Dell(conf-nprefixl)#seq 12 deny 134.23.0.0 /16
Dell(conf-nprefixl)#seq 15 deny 120.23.14.0 /8 le 16
Dell(conf-nprefixl)#show config
!
ip prefix-list juba
seq 12 deny 134.23.0.0/16
seq 15 deny 120.0.0.0/8 le 16
seq 20 permit 0.0.0.0/0 le 32
Dell(conf-nprefixl)#
NOTE:
The last line in the prefix list Juba contains a “permit all” statement. By including this line in a prefix list, you specify
that all routes not matching any criteria in the prefix list are forwarded.
To delete a filter, use the no seq sequence-number command in PREFIX LIST mode.
Access Control Lists (ACLs)
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