Concept Guide

NOTE: It is important to know which protocol your system supports prior to implementing prex-lists.
Conguration Task List for Prex Lists
To congure a prex list, use commands in PREFIX LIST, ROUTER RIP, ROUTER OSPF, and ROUTER BGP modes.
Create the prex 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 conguration tasks for prex lists, as described in the following sections.
• Conguring a prex list
• Use a prex list for route redistribution
For a complete listing of all commands related to prex lists, refer to the Dell Networking OS Command Line Reference Guide.
Creating a Prex List
To create a prex list, use the following commands.
1 Create a prex list and assign it a unique name.
You are in PREFIX LIST mode.
CONFIGURATION mode
ip prefix-list prefix-name
2 Create a prex 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 prex length to match (from 0 to 32).
• le max-prefix-length: the maximum prex length to match (from 0 to 32).
Example of Assigning Sequence Numbers to Filters
If you want to forward all routes that do not match the prex list criteria, congure a prex list lter to permit all routes (permit
0.0.0.0/0 le 32
). The “permit all” lter must be the last lter in your prex list. To permit the default route only, enter permit
0.0.0.0/0.
The following example shows how the seq command orders the lters according to the sequence number assigned. In the example, lter
20 was congured before lter 15 and 12, but the show config command displays the lters 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 prex list Juba contains a “permit all” statement. By including this line in a prex list, you specify that
all routes not matching any criteria in the prex list are forwarded.
To delete a lter, use the no seq sequence-number command in PREFIX LIST mode.
Access Control Lists (ACLs)
135