Reference Guide

Access Control Lists (ACLs) | 91
• Loopback interfaces do not support ACLs using the IP fragment option. If you configure an ACL with
the fragments option and apply it to a loopback interface, the command is accepted, but the ACL
entries are not actually installed the offending rule in CAM.
IP fragments ACL examples
The following configuration permits all packets (both fragmented & non-fragmented) with destination IP
10.1.1.1. The second rule does not get hit at all.
To deny second/subsequent fragments, use the same rules in a different order. These ACLs deny all second
& subsequent fragments with destination IP 10.1.1.1 but permit the first fragment & non fragmented
packets with destination IP 10.1.1.1 .
Layer 4 ACL rules examples
In the below scenario, first fragments non-fragmented TCP packets from 10.1.1.1 with TCP destination
port equal to 24 are permitted. All other fragments are denied.
In the following, TCP packets that are first fragments or non-fragmented from host 10.1.1.1 with TCP
destination port equal to 24 are permitted. Additionally, all TCP non-first fragments from host 10.1.1.1 are
permitted. All other IP packets that are non-first fragments are denied.
FTOS(conf)#ip access-list extended ABC
FTOS(conf-ext-nacl)#permit ip any 10.1.1.1/32
FTOS(conf-ext-nacl)#deny ip any 10.1.1.1./32 fragments
FTOS(conf-ext-nacl)
FTOS(conf)#ip access-list extended ABC
FTOS(conf-ext-nacl)#deny ip any 10.1.1.1/32 fragments
FTOS(conf-ext-nacl)#permit ip any 10.1.1.1/32
FTOS(conf-ext-nacl)
FTOS(conf)#ip access-list extended ABC
FTOS(conf-ext-nacl)#permit tcp host 10.1.1.1 any eq 24
FTOS(conf-ext-nacl)#deny ip any any fragment
FTOS(conf-ext-nacl)
FTOS(conf)#ip access-list extended ABC
FTOS(conf-ext-nacl)#permit tcp host 10.1.1.1 any eq 24
FTOS(conf-ext-nacl)#permit tcp host 10.1.1.1 any fragment
FTOS(conf-ext-nacl)#deny ip any any fragment
FTOS(conf-ext-nacl)