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Brandon Rozek

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Software Developer, Researcher, and Linux Enthusiast.

Multicast Receive Script

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I use socat to debug mutlicast traffic, though the syntax for it is complicated to learn. Here is the command that I normally use to debug multicast traffic.

socat UDP4-RECVFROM:"$port",ip-add-membership="$multicast_address":0.0.0.0,fork -

This says to:

  • Listen to UDP traffic from $port.
  • Subscribe to $multicast_address.
  • 0.0.0.0 means to do it from the interface that matches the routing table for the multicast address.
  • The rest makes it print the traffic to standard out.

To make life easier I created a little script called mrecv that takes a multicast address and port and forms the socat command for me.

#!/bin/bash

show_usage() {
    echo "Usage: mrecv [multicast_address] [port]"
    exit 1
}

contains_help_flag() {
    if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
        return 0
    fi
    return 1
}

if [ "$#" -ne 2 ] ||
   contains_help_flag "$1" ||
   contains_help_flag "$2"; then
    show_usage
fi

multicast_address="$1"
port="$2"

socat UDP4-RECVFROM:"$port",ip-add-membership="$multicast_address":0.0.0.0,fork -
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