Debugging UDP Connections

The most basic network troubleshooting trick in the book is a simple test to make sure that a daemon is listening on its respective port. This is easy with TCP connections because you can simply setup the daemon on the destination and telnet to the port. It’s harder for UDP connections because there is no ACK.

For Solaris, or even better yet illumos:

snoop -d ce0 'host server.example.com and udp and port 137'

ping -U -p 137 server.example.com

If you have linux it’s:

tcpdump -i en1 'host server.example.com and udp and port 137'

See also:
http://www.cosine.org/2007/08/21/debugging-connectivity-problems/

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