Re: Multicast & Tunnel devices

On 29 Apr 2024, at 19:52, Rodney W. Grimes <freebsd-rwg@gndrsh.dnsmgr.net> wrote:
>>> On 29 Apr 2024, at 03:09, Rodney W. Grimes <freebsd-rwg@gndrsh.dnsmgr.net> wrote:
>>> 
>>>> Would anyone know if there is something special with tunnel devices and multicast ? 
>>>> 
>>>> I?ve got some code that happily processes multicast packets on a normal interface; but appears not to do this on a tunnel interface. Tun0 shows multicast enabled:
>>>> 	
>>>> 	tun0: flags=8043<UP,BROADCAST,RUNNING,MULTICAST> metric 0 mtu 1500
>>>> 
>>>> Tcpdump on that interface gives the expected thing (here with mDNS):
>>>> 
>>>> 	tcpdump -n -i tun0 port 5353
>>>> 	listening on tun0, link-type NULL (BSD loopback), capture size 262144 bytes
>>>> 	19:26:03.976259 IP 10.31.0.6.5353 > 224.0.0.251.5353: 0 PTR (QM)? _raop._tcp.local. (34)
>>>> 
>>>> And code, with a simple IP_ADD_MEMBERSHIP  of the MC group on the IP of the local interface below works on a normal interface (e.g. igb0/10.0.0.1/24). 
>>>> 
>>>> 	./listener 10.0.0.1 224.0.0.251 5353
>>> 
>>> Is 10.0.0.1 the IP address of tun0, or is it the address of some other interface?
>>> I suspect that the IP address of the tun0 interface is 10.31.0.6 from your tcpdump above.
>> 
>> That is correct 10.0.0.1/8. 10.31.0.6 is another machine at the other end of the tunnel broadcasting.

Thanks for your reply - it did make play with the several /30’s aliases I was running in parallel on tun0.

And found by accident that if I remove them - things spring to life. Which is actually possible - as I can split the tun0 up into 8 separate /24’s tunnels; one for each connection pair. With that - IP_ADD_MEMBERSHIP does exactly what it says on the tin.

Dw