Listen to UDP data on local port with netcat

listenernetcatudp

netcat -ul -p2115 fails with a usage statement.

What am I doing wrong?

Best Answer

To quote the nc man page:

-l Used to specify that nc should listen for an incoming connection rather than initiate a connection to a remote host. It is an error to use this option in conjunction with the -p, -s, or -z options. Additionally, any timeouts specified with the -w option are ignored.

The key here is that -p cannot be combined with the -l flag. When using the -l flag, any ports specified in the positional arguments are used. So instead, you could use the following:

netcat -ul 2115

Related Solutions

Netcat, Syslog, UDP, and <134>

That is part of the header. "The Priority value is calculated by first multiplying the Facility number by 8 and then adding the numerical value of the Severity." So 134 / 8 = 16 (facility local0) remainder 6 (severity Informational: informational messages).

SYSLOG-MSG      = HEADER SP STRUCTURED-DATA [SP MSG]
HEADER          = PRI...
PRI             = "<" PRIVAL ">"
PRIVAL          = 1*3DIGIT ; range 0 .. 191

Netcat – Listen for Multiple UDP Connections

The author of the ncat tool, in his page for netcat users notes that:

By default, Ncat will accept 100 simultaneous connections, instead of 1 like the original netcat. Use -m to specify the maximum number of simultaneous connections.

I rather suspect this means that netcat won't do what you want, but there's a simple drop-in replacement tool which will.

Best Answer

Related Solutions

Netcat, Syslog, UDP, and <134>

Netcat – Listen for Multiple UDP Connections

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