Limit the number of Telnet sessions coming from the same remote system

There are a few different ways you can limit the number of Telnet sessions coming from the same remote system:

1. Use a firewall to block or limit connections:

You can use a firewall to block incoming Telnet connections from specific IP addresses or networks, or you can use firewall rules to limit the number of connections allowed from a single IP address. This can help prevent a single remote system from establishing too many Telnet sessions.

2. Use TCP Wrappers:

TCP Wrappers is a utility that allows you to control access to network services based on the IP address of the client system. You can use TCP Wrappers to limit the number of Telnet sessions coming from a single IP address by adding a rule to the /etc/hosts.allow file.

For example, to allow a maximum of 2 Telnet sessions from any single IP address, you could add the following rule to /etc/hosts.allow:

in.telnetd : ALL : maxconn 2

3. Use the ulimit command:

The ulimit command allows you to set limits on various system resources, including the number of open file descriptors (which includes network connections). You can use the ulimit command to limit the number of Telnet sessions coming from a single IP address by setting a limit on the number of open file descriptors.

For example, to set a limit of 2 open file descriptors for the telnetd process, you could use the following command:

ulimit -n 2 -u telnetd

Keep in mind that these solutions may not be sufficient to prevent a determined attacker from establishing multiple Telnet sessions. It is generally recommended to use a more secure protocol for remote access, such as SSH, rather than Telnet.