Use iptables to set the number of connections for specific ports (universal method)

Limit the number of port connections

First, enter the command service iptables stop to disable iptables
Limiting the number of concurrent connections on a port is very simple; IPTABLES can handle it. Suppose you want to limit the maximum number of IP connections on port 8388 to 5. Just run these two commands:

iptables -I INPUT -p tcp --dport 8388 -m connlimit --connlimit-above 5 -j DROP
iptables -I OUTPUT -p tcp --dport 8388 -m connlimit --connlimit-above 5 -j DROP

Let me give another example: suppose you want to limit ports from 1024-10240

iptables -I INPUT -p tcp --dport 1024:10240 -m connlimit --connlimit-above 5 -j DROP
iptables -I OUTPUT -p tcp --dport 1024:10240 -m connlimit --connlimit-above 5 -j DROP

Just save the IPTABLES rules (service iptables save); the same applies to other ports.
Enter the command service iptables start to start it
Finally, use the command below to check whether it has taken effect

iptables -L -n -v

Limit Port Speed

First, enter the command service iptables stop to disable iptables
Limiting port concurrency is very simple—IPTABLES can handle it. Suppose you want to limit the maximum connection speed of port 5037 to 60 packets per second; here are the two commands:

iptables -A INPUT -p tcp --sport 5037 -m limit --limit 60/s -j ACCEPT
iptables -A INPUT -p tcp --sport 5037 -j DROP

That is, limit acceptance to 60 packets per second. Generally speaking, each packet is 64—1518 bytes (Byte) in size.

Limit the access speed of a specified IP

Principle: control the rate of a specific port per second. For example, if it exceeds 10 packets per second, DROP them directly, thereby limiting the speed of the specific port.

iptables -A FORWARD -m limit -d 208.8.14.53 --limit 700/s --limit-burst 100 -j ACCEPT
iptables -A FORWARD -d 208.8.14.53 -j DROP

Finally, let’s talk about how to solve the problem of the firewall failing after a reboot

iptables-save >/etc/sysconfig/iptables
echo 'iptables-restore /etc/sysconfig/iptables' >> /etc/rc.local
chmod +x /etc/rc.d/rc.local

For SSR clients

Limit the number of device connections

Open your configuration file. Assuming you installed the ShadowsocksR server in the
/root
folder, it would be:

vi /root/shadowsocksr/user-config.json

Find the protocol parameter (when the parameter is empty “”, the default limit is
64 devices)

"protocol_param": "",

Set the maximum number of device connections for each port in the protocol parameter
(2 minimum recommended). For example, to limit it to a maximum of
5 devices connected at the same time, change it to:

"protocol_param": "5",

Note: The protocol parameter only takes effect when the server-side protocol setting (protocol) is
a non-original (origin) protocol and is not compatible with the original version (_compatible)!

Limit port speed

It’s still the same place mentioned above: the first is the single-thread limit, and the other is the total limit.

"speed_limit_per_con": 0,
"speed_limit_per_user": 0,

When you use this port to download a file, the single-thread download speed limit is 100KB/S.
With multi-threaded downloading (for example, 5 threads), it becomes 500KB/S.
YouTube uses a single thread.

How to Limit Connection Count and Speed in Shadowsocks