User manual

Packet Filters 8-2
5
ICMP Packet Filtering
ICMP packets contain messages exchanged by IP modules in
both hosts and gateways to report errors, problems and
operating information.
You must use generic filter rules to accept or reject ICMP
packets. For more information about generic filters, refer to
Generic Filter Rules on page 8-10.
The ICMP message types are listed below. Note that most of
them are error messages necessary for the correct operation of
TCP/IP:
Type Description
0
Echo Reply (Ping)
3
Destination Unreachable
4
Source Quench
5
Redirect (change route)
8
Echo Request (Ping)
11
Time Exceeded for a Datagram
12
Parameter Problem on a Datagram
13
Timestamp Request
14
Timestamp Reply
15
Information Request
16
Information Reply
17
Address Mask Request
18
Address Mask Reply
IP Call Filtering
You define IP call filtering rules in the IP-CALL protocol section
of the filter file. Like the rules defined in the IP protocol section,
the IP-CALL filtering rules compare the source or destination
network address, host address and port number defined in the
IP-CALL filter rules.