How to verify SQL connectivity on UDP ports using nmap

Most network administrators have at some point or another wished telnet worked for UDP as well as TCP.
Because of UDP being a connectionless transport protocol, scanning UDP ports is a bit more tricky than issuing the command “telnet 25”.

A normal UDP scan will typically yield “open|filtered” because the server does not respond to the UDP packet – or the packet was silently dropped in a firewall.
If there actually was a connection with the server, but no service was running at that particular port, you would get an ICMP Unreachable message and a scan would list the port as “closed”.

Now, using Nmap to verify whether or not UDP port 1434 is open through your firewall, simply issue the following command.

nmap -sU -Pn IP/FQDN -p 1434 -sV

This will work because the -sV switch instructs Nmap to probe potentially open ports for known services.

The switches explained
-sU – “UDP scan”
-Pn – “Treat all hosts as online — skip host discovery”
-sV – “Probe open ports to determine service/version info”
-p – “Only scan specified ports”

Have a look at the picture below to see the difference with and without the -sV switch.


Nmap should be in every network administrators tool chest and is available for a lot of platforms (Unix, Linux, Windows to mention a few).
There is also a portable version for Windows available.

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