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tomdlgns
Premium
join:2003-03-21
Chicago, IL
kudos:1
reply to Wily_One

Re: [Other] DNS errors from The Shining

said by Wily_One:

To test if a DNS server is reachable:
telnet <ip-of-nameserver> 53

If you can make a connection, it tells you two things: 1) the name server is reachable on port 53, and 2) the name server is up and DNS is running.

If you cannot make a connection, could be any number of things, including a firewall somewhere is blocking port 53 or your ISP has no route, etc.

i have used telnet for mail servers and normally see text on the screen after a successful connection. i just tried telnet 8.8.8.8 53 and the cmd prompt was black/blank with a flashing cursor. i tried 8.8.8.23 assuming it was invalid and it times out.

success= flashing cursor

fail= connect fail reply in command prompt

is that accurate?

thanks.


Wily_One
Premium
join:2002-11-24
San Jose, CA
Reviews:
·AT&T U-Verse

1 recommendation

You must be trying telnet from Windows. The Windows telnet client is wonky, hiding any useful connection details that tells you if you've actually connected or not. But yes, a blinking cursor with no error means a successful connection, which means the port is both open and reachable from your client.

To compare, from a Unix/Linux telnet client I get:
$ telnet 8.8.8.8 53
Trying 8.8.8.8...
Connected to google-public-dns-a.google.com (8.8.8.8).
Escape character is '^]'.
Connection closed by foreign host.
 
$ telnet 4.2.2.1 53
Trying 4.2.2.1...
Connected to a.resolvers.level3.net (4.2.2.1).
Escape character is '^]'.
^]
telnet> quit
Connection closed.
 

tomdlgns
Premium
join:2003-03-21
Chicago, IL
kudos:1
yup, using windows. i like seeing something, but good to know that nothing, in this case, is good.

i tried firing up putty, but all i get is a quick flash and the command box (putty) disappears.

i tried 8.8.8.8, raw, port 53 and clicked open.

thanks for the reply.