I have an one firewall table with several entries. Among these one entry is with destination port 23. I don't understand what's the meaning to block destination port 23. After asking my teacher to know that meaning,who said that " This firewall will not allow system in the internet for remotely contacting a particular client because telnet port is blocked. " What did he mean? According to my understanding ,my system isn't allowed to contact with the system where the telnet service that is running on because destination port is 23. Please help me to understand.

  • Honestly, You will have to ask your teacher, what they meant.exactly
    – Ramhound
    Oct 5 at 9:27

Telnet is a remote connection tool similar to SSH, but without the security of SSH. It uses client/server model - a telnet client connects to a telnet server using TCP port 23. Due to lack of security usage of telnet is discouraged in most situations, and firewalls routinely block port 23 to prevent incoming telnet connections.

  • if destination port 23 in firewall means, I am telnet client, I am allowed to reach the telnet server running on port, am I right?
    – nandi
    Oct 5 at 9:16
  • No, it's blocked. Think of a garden - if there's a wall blocking your way you can't get in that way. Oct 5 at 9:30

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