Linux in a Nutshell, Fifth Edition

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Chapter 3: Linux Commands

This is the Title of the Book, eMatter Edition

Copyright © 2006 O’Reilly & Associates, Inc. All rights reserved.

udp

Loaded when -p udp is the only protocol specified:

--source-port [!] [port][:port], --sport [!][port][:port]

Match the specified source ports. The syntax is the same

as for the --source-port option of the TCP extension.

--destination-port [!] [port][:port], --dport [!][port][:port]

Match the specified destination ports. The syntax is the

same as for the --source-port option of the TCP

extension.

Target extensions

Extension targets are optional additional targets supported by sepa-

rate kernel modules. They have their own associated options. We

cover the most frequently used target extensions below.

DNAT

Modify the destination address of the packet and all future

packets in the current connection. DNAT is valid only as a

part of the POSTROUTING chain in the nat table:

--to-destination address[-address][port-port]

Specify the new destination address or range of

addresses. The arguments for this option are the same as

the --to-source argument for the SNAT extension target.

LOG

Log the packet’s information in the system log:

--log-level level

Set the syslog level by name or number (as defined by

syslog.conf).

--log-prefix prefix

Begin each log entry with the string prefix. The prefix

string may be up to 30 characters long.

--log-tcp-sequence

Log the TCP sequence numbers. ...