libxt_connlimit.man

Allows you to restrict the number of parallel connections to a server per
client IP address (or client address block).
.TP
\fB\-\-connlimit\-upto\fP \fIn\fP
Match if the number of existing connections is below or equal \fIn\fP.
.TP
\fB\-\-connlimit\-above\fP \fIn\fP
Match if the number of existing connections is above \fIn\fP.
.TP
\fB\-\-connlimit\-mask\fP \fIprefix_length\fP
Group hosts using the prefix length. For IPv4, this must be a number between
(including) 0 and 32. For IPv6, between 0 and 128. If not specified, the
maximum prefix length for the applicable protocol is used.
.TP
\fB\-\-connlimit\-saddr\fP
Apply the limit onto the source group. This is the default if
\-\-connlimit\-daddr is not specified.
.TP
\fB\-\-connlimit\-daddr\fP
Apply the limit onto the destination group.
.PP
Examples:
.TP
# allow 2 telnet connections per client host
iptables \-A INPUT \-p tcp \-\-syn \-\-dport 23 \-m connlimit \-\-connlimit\-above 2 \-j REJECT
.TP
# you can also match the other way around:
iptables \-A INPUT \-p tcp \-\-syn \-\-dport 23 \-m connlimit \-\-connlimit\-upto 2 \-j ACCEPT
.TP
# limit the number of parallel HTTP requests to 16 per class C sized \
source network (24 bit netmask)
iptables \-p tcp \-\-syn \-\-dport 80 \-m connlimit \-\-connlimit\-above 16
\-\-connlimit\-mask 24 \-j REJECT
.TP
# limit the number of parallel HTTP requests to 16 for the link local network
(ipv6)
ip6tables \-p tcp \-\-syn \-\-dport 80 \-s fe80::/64 \-m connlimit \-\-connlimit\-above
16 \-\-connlimit\-mask 64 \-j REJECT
.TP
# Limit the number of connections to a particular host:
ip6tables \-p tcp \-\-syn \-\-dport 49152:65535 \-d 2001:db8::1 \-m connlimit
\-\-connlimit-above 100 \-j REJECT