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Old 01-12-2017, 05:20 PM   #1
mjl3434
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How to install permanent / persistent multicast route on Ubuntu


My question is: How do I configure a multicast route in Ubuntu such that it will always be present even after a reboot, and will not be removed automatically by any networking daemons Ubuntu runs?

Here is some background of my situation and what I've tried. I am stuck with Ubuntu 16.04 LTS and cannot change that. I cannot install any updates as it may break undocumented dependencies in my fragile build system (don't ask). I can add new software which is not already present. I have multiple interfaces on my Linux server and I need to have a permanent multicast route configured. I tried manually entering the route with:

Code:
user@hostname:~$ sudo ip route add 239.192.0.85/32 dev enp5s2
and everything worked excellently as confirmed by:

Code:
user@hostname:~$ route -n  | grep 239
239.192.0.85    0.0.0.0         255.255.255.255 UH    0      0        0 enp5s2
BUT NO DICE!!! -- After some time passes my route disappears.

It seems like Ubuntu has some sort of networking daemon running in the background who's main job seems to be going around and undoing any of the work someone has done manually and deliberately unless they have done it THE ONE AND ONLY CORRECT WAY (whatever that is?).

I tried to install the route using Ubuntu's gui (unity-control-center network) and there was a spot for IPv4 and routes, however when I enter a multicast route it does not work as desired. The gui shows the configuration as a static IP address. Then once I save and close out the gui no multicast route or secondary IP is added anyway proving that the gui seems to be pretty worthless for anything beyond the most basic configuration.

I also tried adding a route to /etc/network/interfaces but it does not seem to have any effect when I restart the whole machine, or when I restart NetworkManager (which might not even be the right way to apply the settings).
 
Old 01-17-2017, 04:28 PM   #2
nini09
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IGMP could join and leave a multicast group.
 
Old 01-18-2017, 12:40 PM   #3
mjl3434
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Quote:
IGMP could join and leave a multicast group.
Correct, IGMP can be used to inform an upstream router, or switch that supports IGMP snooping, about the need to update their multicast routing tables. However I'm trying to add this multicast route to a host, so IGMP is irrelevant. My problem is that I want to add a persistent route to the host. I could use the crummy Ubuntu GUI tools if it were a traditional unicast route, but I tried it with multicast and that use case wasn't properly supported. So now I need to really know how to disable Ubuntu's background daemons which screw with the networking. From there I can add a startup script which installs the route. That's no problem. Perhaps I should rephrase my question and ask the Ubuntu user's forum.
 
Old 01-18-2017, 04:14 PM   #4
nini09
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The host just need to join multicast group. IGMP or PIM will take care of multicast routing or route update.
 
  


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