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Stupid Telnet Question

Just a quick one here - I use telnet often to test connectivity to devices through specific ports to ensure they are not blocked.

I've always assume that these were TCP ports.  Is it possible to do the same, but use UDP instead?  Or should telnet work regardless is the listening port is TCP or UDP?
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Chris AshcraftSenior Analyst - Technology
BRONZE EXPERT
Commented:
Telnet runs on TCP/IP at the application layer. To my knowledge it's not possible to connect to a port using a connectionless protocol such as UDP with Telnet.
Dave BaldwinFixer of Problems
SILVER EXPERT
Most Valuable Expert 2014
Commented:
UDP doesn't "connect", it just sends messages and doesn't not require a response.  So unless your device is programmed to respond, just sending a UDP message won't tell you anything.
Senior Systems Admin
BRONZE EXPERT
Top Expert 2010
Commented:
Telnet relies on TCP which requires a "Three-way handshake" to complete a connection. UDP doesn't do this, and so connecting to a UDP port over TCP will not complete a proper connection.

You can attempt to listen for or talk to UDP ports by using a utility called Netcat. http://netsecure.alcpress.com/netcat/ has more information.

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Commented:
Thanks all.  As I thought.

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