UDP Multicast doesn't work on MacOS

[ihilt]

In particular, these commands:

sudo ifconfig lo multicast
sudo route add -net 224.0.0.0 netmask 240.0.0.0 dev lo

fail since lo does not exist.

Changing lo to lo0 made further progress but route does not appear to have a netmask specifier. The following was accepted:

sudo route -nv add -net 224.0.0.0 -interface lo0

However the LCM self test continued to fail.

[SuryaB1]

I am encountering the same issue.

[drmoose]

If you don't specify a netmask, route will assume you want 255.255.255.255. Modern macos's route implementation seems to expect a CIDR subnet instead of a netmask, and the equivalent of 240.0.0.0 is /4, so try:

sudo route -nv add -net 224.0.0.0/4 -interface lo0

You can verify it's working with netstat -rn, which should have an entry in its ipv4 table like this:

Internet:
Destination        Gateway            Flags               Netif Expire
...snip...
224                lo0                USc                   lo0      

[danielcjacobs]

Can confirm that sudo route -nv add -net 224.0.0.0/4 -interface lo0 worked.

Seems by default, my mac already had an entry for 224.0.0/4 in its routing table, but it was being directed through en0 instead of lo0. As a result I got the following error when running the above command:

$ sudo route -nv add -net 224.0.0.0/4 -interface lo0
u: inet 224.0.0.0; u: link lo0; u: inet 240.0.0.0; RTM_ADD: Add Route: len 136, pid: 0, seq 1, errno 0, flags:<UP,STATIC>
locks:  inits: 
sockaddrs: <DST,GATEWAY,NETMASK>
 224.0.0.0 lo0 240.0.0.0
route: writing to routing socket: File exists
add net 224.0.0.0: gateway lo0: File exists

I just had to remove the en0 entry from my routing table and then it worked:

sudo route -nv delete 224.0.0/4
sudo route -nv add -net 224.0.0.0/4 -interface lo0

[danielcjacobs]

Seems closely related to #60