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(?) DNS and telnet

From crabe

Answered By Mike Orr

Hi, How do you get telnet working on your own machine as referred to in the DNS HOWTO, i.e telnetting at 127.0.0.1 ? I got telnet working to reach my ISP but never got around telnetting 127.0.0.1. So I gave up DNS. I have looked around all the HOWTOs available, and perhaps it's too simple for mentionning. I am running LinuxPPC2000. Thanks for any answer.

(!) [Mike] Are you trying to do a standard telnet ("telnet 127.0.0.1") or telnet to another port ("telnet 127.0.0.1 53" would be a DNS query)? Here are a few possibilities:
  1. Nobody is listening on the telnet port. If so, you'll get an immediate "connection refused" error. Telnetd is normally started from inetd. Uncomment the telnet line in /etc/inetd.conf and "killall -HUP inetd".
  2. Your loopback devide is not configured. What happens when you run "ping 127.0.0.1"? If you get no response, do "ifconfig". There should be a stanza for device "lo". If not, run "ifconfig lo 127.0.0.1" and/or "ifconfig 127.0.0.1 up". (If you're still running kernel 2.0.x, follow that with "route add -net 127.0.0.0"). Then look at your network startup scripts to see why it isn't being activated by default.
  3. Inetd runs telnet through a tcpd wrapper for security, and you're failing the tcpd check. This would cause the connection to do nothing (at least nothing visible) and then disconnect after a couple seconds. See "man tcpd" and "man 5 hosts_access".
  4. You are telnetting to port 53 and your nameserver is not running. If so, you'd get a "connection refused" error. If you installed named (bind), find out why it isn't running.
The TAG security hawks will send a follow-up if I don't also mention that telnet is a security risk bla bla bla because it doesn't encrypt your password or your data. Think twice before running telnetd, and think a third time before allowing tcpd to allow telnet connections from outside your local network.

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