iptables的man手册里面有详细的说明,还有使用的例子。
connlimit
Allows you to restrict the number of parallel TCP connections to a server per client IP address (or address
block).
[!] --connlimit-above n
match if the number of existing tcp connections is (not) above n
--connlimit-mask bits
group hosts using mask
Examples:
# allow 2 telnet connections per client host
iptables -p tcp --syn --dport 23 -m connlimit --connlimit-above 2 -j REJECT
# you can also match the other way around:
iptables -p tcp --syn --dport 23 -m connlimit ! --connlimit-above 2 -j ACCEPT
# limit the nr of parallel http requests to 16 per class C sized network (24 bit netmask)
iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 16 --connlimit-mask 24 -j REJECT