Reference Guide

Access Control Lists (ACLs) | 105
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.
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)
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.
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)
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.
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)
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 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)
To log all the packets denied and to override the implicit deny rule and the implicit permit rule for TCP/
UDP fragments, use a configuration similar to the following.
FTOS(conf)#ip access-list extended ABC
FTOS(conf-ext-nacl)#permit tcp any any fragment
FTOS(conf-ext-nacl)#permit udp any any fragment
FTOS(conf-ext-nacl)#deny ip any any log
FTOS(conf-ext-nacl)