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Chapter 3 - Additional Features
User Guide
163
UDP Extension
These extensions are loaded if the protocol udp is specified or “-m udp” is specified. It
provides the following options:
ICMP Extension
This extension is loaded if the protocol icmp is specified or “-m icmp” is specified. It provides
the following option:
Multiport Extension
This module matches a set of source or destination ports. Up to 15 ports can be specified. It
can only be used in conjunction with -m tcp or -m udp.
[!] - -syn
Only match TCP packets with the SYN bit set and the
ACK and FIN bits cleared. Such packets are used to
request TCP connection initiation; for example, block-
ing such packets coming in an interface will prevent
incoming TCP connections, but outgoing TCP con-
nections will be unaffected. It is equivalent to
- -tcp-flags SYN,RST,ACK SYN.
If the "!" flag precedes the "- -syn," the sense of the
option is inverted.
- -tcp-option [!] number
Match if TCP option set.
- -source-port [!] [port[:port]]
Source port or port range specification. See the
description of the - -source-port option of the TCP
extension for details.
- -destination-port [!] [port[:port]]
Destination port or port range specification. See
the description of the - -destination-port option of
the TCP extension for details.
- -icmp-type [!] typename
This allows specification of the ICMP type, which
can be a numeric ICMP type, or one of the ICMP
type names shown by the command
iptables -p icmp -h