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Dell(conf-policy-map-in)#exit
Dell(conf)#interface tengig 1/0
Dell(conf-if-te-1/0)#service-policy input pmap
IP Fragment Handling
The system 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 uses a significant number of CAM entries per TCP/UDP entry.
• For an IP ACL, the system always applies implicit deny. You do not have to configure it.
• For an IP ACL, the system applies implicit permit for second and subsequent fragment just prior to the
implicit deny.
• If you configure an explicit deny, the second and subsequent fragments do 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.
IP Fragments ACL Examples
The following examples show how you can use ACL commands with the fragment keyword to filter
fragmented packets.
Example of Permitting All Packets on an Interface
The following configuration permits all packets (both fragmented and non-fragmented) with destination
IP 10.1.1.1. The second rule does not get hit at all.
Dell(conf)#ip access-list extended ABC
Dell(conf-ext-nacl)#permit ip any 10.1.1.1/32Dell(conf-ext-nacl)#deny ip any
10.1.1.1./32 fragments
Dell(conf-ext-nacl)
Example of Denying Second and Subsequent Fragments
To deny the second/subsequent fragments, use the same rules in a different order. These ACLs deny all
second and subsequent fragments with destination IP 10.1.1.1 but permit the first fragment and non-
fragmented packets with destination IP 10.1.1.1.
Dell(conf)#ip access-list extended ABC
Dell(conf-ext-nacl)#deny ip any 10.1.1.1/32 fragments
Dell(conf-ext-nacl)#permit ip any 10.1.1.1/32
Dell(conf-ext-nacl)
Layer 4 ACL Rules Examples
The following examples show the ACL commands for Layer 4 packet filtering.
Permit an ACL line with L3 information only, and the fragments keyword is present:
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Access Control Lists (ACLs)