Reference Guide

Applying a Filter to a Prefix List (OSPF)
To apply a filter to routes in open shortest path first (OSPF), use the following commands.
• Enter OSPF mode.
CONFIGURATION mode
router ospf
• Apply a configured prefix list to incoming routes. You can specify an interface.
If you enter the name of a non-existent prefix list, all routes are forwarded.
CONFIG-ROUTER-OSPF mode
distribute-list prefix-list-name in [interface]
• Apply a configured prefix list to incoming routes. You can specify which type of routes are affected.
If you enter the name of a non-existent prefix list, all routes are forwarded.
CONFIG-ROUTER-OSPF mode
distribute-list prefix-list-name out [connected | rip | static]
To view the configuration, use the show config command in ROUTER OSPF mode, or the show running-
config ospf
command in EXEC mode.
Example of Viewing Configured Prefix Lists (ROUTER OSPF mode)
FTOS(conf-router_ospf)#show config
!
router ospf 34
network 10.2.1.1 255.255.255.255 area 0.0.0.1
distribute-list prefix awe in
FTOS(conf-router_ospf)#
ACL Resequencing
ACL resequencing allows you to re-number the rules and remarks in an access or prefix list.
The placement of rules within the list is critical because packets are matched against rules in sequential order. To order
new rules using the current numbering scheme, use resequencing whenever there is no opportunity.
For example, the following table contains some rules that are numbered in increments of 1. You cannot place new rules
between these packets, so apply resequencing to create numbering space, as shown in the second table. In the same
example, apply resequencing if more than two rules must be placed between rules 7 and 10.
You can resequence IPv4 and IPv6 ACLs, prefixes, and MAC ACLs. No CAM writes happen as a result of resequencing,
so there is no packet loss; the behavior is similar Hot-lock ACLs.
NOTE: ACL resequencing does not affect the rules, remarks, or order in which they are applied. Resequencing
merely renumbers the rules so that you can place new rules within the list as needed.
Table 7. ACL Resequencing
Rules Resquencing
Rules Before Resequencing: seq 5 permit any host 1.1.1.1
seq 6 permit any host 1.1.1.2
seq 7 permit any host 1.1.1.3
seq 10 permit any host 1.1.1.4
113