Administrator Guide

The following examples show permit or deny filters for specific routes using the le and ge parameters, where x.x.x.x/x
represents a route prefix:
● To deny only /8 prefixes, enter deny x.x.x.x/x ge 8 le 8.
● To permit routes with the mask greater than /8 but less than /12, enter permit x.x.x.x/x ge 8.
● To deny routes with a mask less than /24, enter deny x.x.x.x/x le 24.
● To permit routes with a mask greater than /20, enter permit x.x.x.x/x ge 20.
The following rules apply to prefix lists:
● A prefix list without any permit or deny filters allows all routes.
● An “implicit deny” is assumed (that is, the route is dropped) for all route prefixes that do not match a permit or deny filter in
a configured prefix list.
● After a route matches a filter, the filter’s action is applied. No additional filters are applied to the route.
Implementation Information
In Dell EMC Networking OS, 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 EMC Networking OS Command Line Interface
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.
Access Control Lists (ACLs)
121