Reference Guide

Access Control Lists (ACLs) | 67
Figure 6-1. Using the Order Keyword in ACLs
IP Fragment Handling
FTOS supports a configurable option to explicitly deny IP fragmented packets, particularly second and
subsequent packets. It extends the existing ACL command syntax with the
fragments keyword for all
Layer 3 rules applicable to all Layer protocols (permit/deny ip/tcp/udp/icmp).
• Both standard and extended ACLs support IP fragments.
• Second and subsequent fragments are allowed because a Layer 4 rule cannot be applied to these
fragments. If the packet is to be denied eventually, the first fragment would be denied and hence the
packet as a whole cannot be reassembled.
• Implementing the required rules will use a significant number of CAM entries per TCP/UDP entry.
• For IP ACL, FTOS always applies implicit deny. You do not have to configure it.
• For IP ACL, FTOS applies implicit permit for second and subsequent fragment just prior to the
implicit deny.
• If an explicit deny is configured, the second and subsequent fragments will not hit the implicit permit
rule for fragments.
• 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.
FTOS(conf)#ip access-list standard acl1
FTOS(config-std-nacl)#permit 20.0.0.0/8
FTOS(config-std-nacl)#exit
FTOS(conf)#ip access-list standard acl2
FTOS(config-std-nacl)#permit 20.1.1.0/24 order 0
FTOS(config-std-nacl)#exit
FTOS(conf)#class-map match-all cmap1
FTOS(conf-class-map)#match ip access-group acl1
FTOS(conf-class-map)#exit
FTOS(conf)#class-map match-all cmap2
FTOS(conf-class-map)#match ip access-group acl2
FTOS(conf-class-map)#exit
FTOS(conf)#policy-map-input pmap
FTOS(conf-policy-map-in)#service-queue 7 class-map cmap1
FTOS(conf-policy-map-in)#service-queue 4 class-map cmap2
FTOS(conf-policy-map-in)#exit
FTOS(conf)#interface te 10/0
FTOS(conf-if-te-10/0)#service-policy input pmap