| 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. |
| .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 |
