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Telnet cmd to check open ports

Telnet cmd to check open ports

(OP)
Hi mates,

My doubt is about using telnet to see open ports remotely.

For example, there are sometimes when you use telnet x.x.x.x (port) to check open ports right ?
So, if I'm checking DNS (port 53) to see if it is running, and I don't receive responses it means the port is closed ?
because I did the same with a public DNS (8.8.8.8) and I get a prompt when using cmd.

Thanks for any advice....

RE: Telnet cmd to check open ports

If you attempt to telnet to a port and do not get a response, as in the connection times out, it MAY mean that the port is closed. Telnet is used to establish a fairly raw and generic connection to a service. It isn't a really good tool for determining if ports are open, for that the nmap utility would work much better. In order for a port to be open, it has to both have a process listening on that port and have appropriate firewall settings on any devices upstream.

RE: Telnet cmd to check open ports

Don't forget that (mostly) DNS uses UDP, and telnet will try to open a TCP connection!

Some DNS servers will respond on TCP/53 (like 8.8.8.8), but not all!

Take Care

Matt
I have always wished that my computer would be as easy to use as my telephone.
My wish has come true. I no longer know how to use my telephone.

RE: Telnet cmd to check open ports

(OP)
Ok.

Thanks for your clear responses.

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