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Allows you to restrict the number of parallel connections to a server per
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client IP address (or client address block).
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[\fB!\fR] \fB--connlimit-above \fIn\fR
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Match if the number of existing connections is (not) above \fIn\fR.
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\fB--connlimit-mask\fR \fIprefix_length\fR
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Group hosts using the prefix length. For IPv4, this must be a number between
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(including) 0 and 32. For IPv6, between 0 and 128.
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# allow 2 telnet connections per client host
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iptables -A INPUT -p tcp --syn --dport 23 -m connlimit --connlimit-above 2 -j REJECT
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# you can also match the other way around:
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iptables -A INPUT -p tcp --syn --dport 23 -m connlimit ! --connlimit-above 2 -j ACCEPT
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# limit the number of parallel HTTP requests to 16 per class C sized \
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network (24 bit netmask)
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iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 16
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--connlimit-mask 24 -j REJECT
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# limit the number of parallel HTTP requests to 16 for the link local network \
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ip6tables -p tcp --syn --dport 80 -s fe80::/64 -m connlimit --connlimit-above
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16 --connlimit-mask 64 -j REJECT