Reference Guide
IP Access Control Lists (ACL), Prefix Lists, and Route-maps | 151
Configuration Task List for Prefix Lists
To configure a prefix list, you must use commands in the PREFIX LIST, the ROUTER RIP, ROUTER
OSPF, and ROUTER BGP modes. Basically, you create the prefix list in the PREFIX LIST mode, and
assign that list to commands in the ROUTER RIP, ROUTER OSPF and ROUTER BGP modes.
The following list includes the configuration tasks for prefix lists:
• Configure a prefix list
• Use a prefix list for route redistribution
For a complete listing of all commands related to prefix lists, refer to the
FTOS Command Line Interface
Reference document.
Configure a prefix list
To configure a prefix list, use these commands in the following sequence, starting in the
CONFIGURATION mode:
If you want to forward all routes that do not match the prefix list criteria, you must configure a prefix list
filter to permit all routes (
permit 0.0.0.0/0 le 32). The “permit all” filter should be the last filter in your
prefix list. To permit the default route only, enter
permit 0.0.0.0/0.
The following example illustrates 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.
FTOS(conf-nprefixl)#seq 20 permit 0.0.0.0/0 le 32
FTOS(conf-nprefixl)#seq 12 deny 134.23.0.0 /16
FTOS(conf-nprefixl)#seq 15 deny 120.23.14.0 /8 le 16
FTOS(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
FTOS(conf-nprefixl)#
Step Command Syntax Command Mode Purpose
1 ip prefix-list prefix-name CONFIGURATION Create a prefix list and assign it a unique name.
You are in the PREFIX LIST mode.
2
seq sequence-number
{deny | permit} ip-prefix
[ge min-prefix-length] [le
max-prefix-length]
CONFIG-NPREFIXL Create a prefix list with a sequence number and a deny
or permit action. The optional parameters are:
• ge min-prefix-length: is the minimum prefix
length to be matched (0 to 32).
• le max-prefix-length: is the maximum prefix
length to be matched (0 to 32).