Fragmented Packet Handling

Two keywords are used to support fragmentation in ACLs:

fragments—FO field = 0 (FO means the fragment offset field in the IP header). This will match first fragment also (packets with FO = 0).
first-fragments—FO == 0.

Policy file syntax checker

The fragments keyword cannot be used in a rule with L4 information. The syntax checker will reject such policy files.

The following rules are used to evaluate fragmented packets or rules that use the fragments or first-fragments keywords.

With no keyword specified, processing proceeds as follows:

An L3-only rule that does not contain either the fragments or first-fragments keyword matches any IP packets.
An L4 rule that does not contain either the fragments or first-fragments keyword matches non-fragmented or initial-fragment packets.

With the fragments keyword specified:

With the first-fragments keyword specified:

An L3-only rule with the first-fragments keyword matches initial fragment packets.
An L4 rule with the first-fragments keyword matches initial fragment packets.

Published March 2020prev | next