@Critchleyb I have thought about this a bit more. Most issues arise when you try to multicast across switches and even more across routers/subnets. This can be very hard to get to work properly if you’re not one of these network wizards. But you said you had the problem even when multicasting clients all being on the same switch. This rules out the switch from my point of view as all switches I have seen handle multicast within their own fabrics fairly well.
You might want to test with iPerf to see if you get the same results. Using iPerf you might get a feeling of what’s going on in your network. For that edit /images/dev/postinitscripts/fog.postinit on your FOG server (be careful, this will be used by every client doing a task so better don’t do this in an environment where someone else might be using this FOG sever to deploy clients at the same time) to look like this:
#!/bin/bash
## This file serves as a starting point to call your custom pre-imaging/post init loading scripts.
## <SCRIPTNAME> should be changed to the script you're planning to use.
## Syntax of post init scripts are
#. ${postinitpath}<SCRIPTNAME>
curl -ko iperf https://iperf.fr/download/ubuntu/iperf_2.0.9
chmod +x iperf
./iperf -s -u -B 224.0.0.1 -p 9000 -i 1
Now also install iperf on your FOG server. Make sure it’s version 2.x as the newer 3.x does not support multicast testing anymore. Most distros should have it in the repos or you can get it here.
Get together a couple of clients you want to test with and manually schedule a debug task for those (doesn’t matter if it’s capture or deploy as we don’t want to run the task itself anyway). You cannot schedule as debug via group so this has to be done individually for each host. Let them all boot up and hit ENTER twice to get to the shell. Then start the iperf test simply by running the command fog. Do this with all your test clients and let them wait there.
Now back to the FOG server run this command to start the test: iperf -c 224.0.0.1 -u -p 9000 -i 1 -b 1000M -t 10
This will do a first 10 second test with max bandwidth of 1000MBit/s. Adjust the last two parameters and start the test runs from your FOG server as often as you like. Once the clients are up and waiting you can start testing from the server again and again without touching the clients.
Although you only get the interesting results watching the client’s screens. You see transfer rates and more importantly lost packets (in total and percent).
Hint: The logic of client/server is a bit reverse in this iPerf test. In multicast mode you want one client (the FOG server) to send data to all your multicast server listeners (hosts).