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44 lines
1.7 KiB
44 lines
1.7 KiB
4 months ago
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These extensions can be used if `\-\-protocol tcp' is specified. It
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provides the following options:
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.TP
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[\fB!\fP] \fB\-\-source\-port\fP,\fB\-\-sport\fP \fIport\fP[\fB:\fP\fIport\fP]
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Source port or port range specification. This can either be a service
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name or a port number. An inclusive range can also be specified,
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using the format \fIfirst\fP\fB:\fP\fIlast\fP.
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If the first port is omitted, "0" is assumed; if the last is omitted,
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"65535" is assumed.
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The flag
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\fB\-\-sport\fP
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is a convenient alias for this option.
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.TP
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[\fB!\fP] \fB\-\-destination\-port\fP,\fB\-\-dport\fP \fIport\fP[\fB:\fP\fIport\fP]
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Destination port or port range specification. The flag
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\fB\-\-dport\fP
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is a convenient alias for this option.
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.TP
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[\fB!\fP] \fB\-\-tcp\-flags\fP \fImask\fP \fIcomp\fP
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Match when the TCP flags are as specified. The first argument \fImask\fP is the
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flags which we should examine, written as a comma-separated list, and
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the second argument \fIcomp\fP is a comma-separated list of flags which must be
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set. Flags are:
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.BR "SYN ACK FIN RST URG PSH ALL NONE" .
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Hence the command
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.nf
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iptables \-A FORWARD \-p tcp \-\-tcp\-flags SYN,ACK,FIN,RST SYN
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.fi
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will only match packets with the SYN flag set, and the ACK, FIN and
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RST flags unset.
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.TP
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[\fB!\fP] \fB\-\-syn\fP
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Only match TCP packets with the SYN bit set and the ACK,RST and FIN bits
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cleared. Such packets are used to request TCP connection initiation;
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for example, blocking such packets coming in an interface will prevent
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incoming TCP connections, but outgoing TCP connections will be
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unaffected.
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It is equivalent to \fB\-\-tcp\-flags SYN,RST,ACK,FIN SYN\fP.
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If the "!" flag precedes the "\-\-syn", the sense of the
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option is inverted.
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.TP
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[\fB!\fP] \fB\-\-tcp\-option\fP \fInumber\fP
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Match if TCP option set.
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