Telnet ошибка порт 23

The telnet command connects to the host you specify as the first argument on the port you specify as the second argument (or 23, if you only specify a single argument).

When you tried to execute telnet port, it tried to connect to the server port on port 23. Since there is no server with the address port (unless you specified it in your pc’s hosts file), telnet couldn’t connect to it.

I’m guessing the second command failed, because www.udacity.com doesn’t accept connections on port 8080 (the second argument of the command).

I don’t see any instructions in the link you provided.

EDIT: If you’re trying to connect to localhost, use telnet localhost (to connect to port 23) or telnet localhost <port> (replace <port> with the port you are trying to connect to).

Given that ssh works but telnet doesn’t, there are a few options:

• A firewall is blocking the traffic on the server
• Telnet is not running on the server
• Your connections are routed through a gateway that filters out telnet traffic
• You typed different ip addresses when you tried to connect via ssh / telnet

1. It could be your server’s firewall that’s blocking the connection.

As a quick check, add (temporary) rules to allow all the traffic:

[root@server]# iptables -I INPUT 1 -j ACCEPT
[root@server]# iptables -I OUTPUT 1 -j ACCEPT

You might as well do the same on the client to get that out of the way.
When you’re done testing (at the end of this message), remove these two with

[root@server]# iptables -D INPUT 1
[root@server]# iptables -D OUTPUT 1

2. Your server is missing a route for its 192.18.209.0/24 (?) subnet

Your server’s routing table is weird. You said its IP address was 192.18.209.124, but the routing table says it’s 192.18.212.124 . Did you change it to the 212 subnet to test some things? If so, can you revert it back to the state it was when you wrote your first message?

Do traceroutes from the server to the client and vice versa to check the paths are correct.

3. Full testing sequence, ONLY if you have a physical access to the server (as you might lose network access due to the potential ip change)

Assuming your topology is a very simple one with both machines on the same network as on the following diagram:

        +---------+                  Server: 192.18.209.124/24
        | Switch  |                  CentOS: 192.18.209.87 /24
        +---------+
     _____|     |_____
    |                 |
+--------+        +--------+
| Server |        | CentOS |
+--------+        +--------+

[root@server] iptables -I INPUT 1 -j ACCEPT
[root@server] iptables -I OUTPUT 1 -j ACCEPT
[root@server] ifconfig eth2 192.18.209.124/24
[root@server] netstat -tapn | grep :23

[root@centos] iptables -I INPUT 1 -j ACCEPT
[root@centos] iptables -I OUTPUT 1 -j ACCEPT
[root@centos] traceroute 192.18.209.124
[root@centos] nc -vv 192.18.209.124 23

[root@server] traceroute 192.18.209.87
[root@server] iptables -D INPUT 1
[root@server] iptables -D OUTPUT 1

[root@centos] iptables -D INPUT 1
[root@centos] iptables -D OUTPUT 1