2020-11-23 23:47:16 -05:00
---
title: "Multicast Receive Script"
date: 2020-11-18T10:09:15-05:00
draft: false
2022-01-02 14:24:29 -05:00
tags: ["Linux", "Networking"]
2020-11-23 23:47:16 -05:00
---
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.
```bash
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.
```bash
#!/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 -
```
