How to Restrict the Number of Parallel Connections Using IPtables?

[lijeshk]

We can use connlimit module to put such restrictions.

To allow 3 ssh connections per client host, enter:

Code: [Select]

# iptables -A INPUT -p tcp --syn --dport 22 -m connlimit --connlimit-above 3 -j REJECT
Set HTTP requests to 20:

Code: [Select]

# iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 20 --connlimit-mask 24 -j DROP
Where,

--connlimit-above 3 : Match if the number of existing connections is above 3.

--connlimit-mask 24 : Group hosts using the prefix length. For IPv4, this must be a number between (including) 0 and 32.

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