UDPXY command line arguments

usage: udpxy [-vTS] [-a listenaddr] -p port [-m mcast_ifc_addr] [-c clients] [-l logfile] [-B sizeK] [-n nice_incr]
-v : enable verbose output [default = disabled]
-S : enable client statistics [default = disabled]
-T : do NOT run as a daemon [default = daemon if root]
-a : (IPv4) address/interface to listen on [default = 0.0.0.0]
-p : port to listen on
-m : (IPv4) address/interface of (multicast) source [default = 0.0.0.0]
-c : max clients to serve [default = 3, max = 5000]
-l : log output to file [default = stderr]
-B : buffer size (65536, 32Kb, 1Mb) for inbound (multicast) data [default = 2048 bytes]
-R : maximum messages to store in buffer (-1 = all) [default = 1]
-H : maximum time (sec) to hold data in buffer (-1 = unlimited) [default = 1]
-n : nice value increment [default = 0]
-M : periodically renew multicast subscription (skip if 0 sec) [default = 0 sec]

More info: mankier.com

Bonus, reading the multicast ip from ifconfig:
udpxy -m $(ifconfig vlan2 | grep 'inet addr:' | sed -e 's/.*inet addr://' -e 's/ *Bcast.*//')