Multicast over GRE tunnel

hobbes159 · Sat Mar 09, 2024 7:58 pm

I have two sites. One site has a multicast-audio based alerting system (alerts are played over multicast-compatible phones). I'd like to extend that alerting capability so that multicast audio played on site A can be received at site B. Both sites are already connected over a VPN (Meraki), and I have RouterOS devices at each site, and devices can ping each other over the existing VPN. Multicast audio is transmitted on 239.1.0.0/24 on Site A.

So far I have a working GRE tunnel between the two sites, and setup static RP which shows up in each site's "Neighbor" listing. I'm rather at a loss at this point, however. Packet sniffing shows that multicast played at site A isn't being repeated at Site B. I'm missing something, but haven't had much luck finding a solution. The Mikrotik documentation seems a bit thin. Any suggestions on how I can get this to work?

Site A (192.168.1.0/24) ----- VPN ----- Site B (192.168.10.0/24)
Router A (192.168.1.50) --------------- Router B (192.168.10.60)

admin@RouterA /interface/gre> print
Flags: X - disabled; R - running
 0  R name="gre-tunnel1" mtu=auto actual-mtu=1476 local-address=0.0.0.0 remote-address=192.168.10.60 keepalive=10s,10 dscp=inherit clamp-tcp-mss=yes dont-fragment=no
      allow-fast-path=yes

admin@RouterB /interface/gre> print
Flags: X - disabled; R - running
 0  R name="gre-tunnel1" mtu=auto actual-mtu=1476 local-address=0.0.0.0 remote-address=192.168.1.50 keepalive=10s,10 dscp=inherit clamp-tcp-mss=yes dont-fragment=no
      allow-fast-path=yes

 admin@RouterA /ip/address> print
Columns: ADDRESS, NETWORK, INTERFACE
# ADDRESS            NETWORK       INTERFACE
0 192.168.1.50/24  192.168.1.0  ether1
1 172.1.1.1/30       172.1.1.0     gre-tunnel1

admin@RouterB /ip/address> print
Columns: ADDRESS, NETWORK, INTERFACE
# ADDRESS            NETWORK       INTERFACE
0 192.168.10.60/24  192.168.10.0  ether1
1 172.1.1.2/30       172.1.1.0     gre-tunnel1

admin@RouterA /routing/pimsm/instance> print
Columns: VRF, NAME
# VRF   NAME
0 main  pimsm-instance1

admin@RouterB /routing/pimsm/instance> print
Columns: VRF, NAME
# VRF   NAME
0 main  pimsm-instance1

admin@RouterA /routing/pimsm/interface-template> print
Columns: INSTANCE, INTERFACES
# INSTANCE         INTERFACES
0 pimsm-instance1  ether1
                   lo
                   gre-tunnel1

admin@RouterB /routing/pimsm/interface-template> print
Columns: INSTANCE, INTERFACES
# INSTANCE         INTERFACES
0 pimsm-instance1  ether1
                   lo
                   gre-tunnel1
                   
admin@RouterA /routing/pimsm/static-rp> print
Flags: X - disabled, I - inactive
 0   instance=pimsm-instance1 group=239.10.0.0/24 address=172.1.1.1

admin@RouterB /routing/pimsm/static-rp> print
Flags: X - disabled, I - inactive
 0   instance=pimsm-instance1 group=239.10.0.0/24 address=172.1.1.1
 
admin@RouterA /routing/pimsm/neighbor> print
Flags: J - JOIN-TRACKING
Columns: INSTANCE, ADDRESS, PRIORITY
#   INSTANCE         ADDRESS                PRIORITY
0 J pimsm-instance1  172.1.1.2%gre-tunnel1         1

admin@RouterB /routing/pimsm/neighbor> print
Flags: J - JOIN-TRACKING
Columns: INSTANCE, ADDRESS, PRIORITY
#   INSTANCE         ADDRESS                PRIORITY
0 J pimsm-instance1  172.1.1.1%gre-tunnel1         1

admin@RouterA /ip/route> print
Flags: D - DYNAMIC; A - ACTIVE; c - CONNECT, s - STATIC
Columns: DST-ADDRESS, GATEWAY, DISTANCE
#     DST-ADDRESS     GATEWAY      DISTANCE
0  As 0.0.0.0/0       192.168.1.1         1
  DAc 172.1.1.0/30    gre-tunnel1         0
  DAc 192.168.0.0/23  bridge1             0
1  As 239.10.0.0/24   172.1.1.2           1

Amm0 · Sat Mar 09, 2024 10:50 pm

See viewtopic.php?t=185669

hobbes159 · Sun Mar 10, 2024 1:31 am

See viewtopic.php?t=185669

That was one of the sources I used when getting as far as I have. Unfortunately, it appears that the original poster didn't get a resolution to their problem, and was stuck at about the same point I'm at. GRE tunnel is up, static-RP is set up, but no multicast traffic is being transported across the link. I was hoping that someone would give the problem a fresh look and see what I'm missing.

Amm0 · Sun Mar 10, 2024 2:35 am

I guess I was hoping it was fixed... I've seen fixed in RNs... but not tested routed multicast myself.

One thing to keep in mind with a tunnel involved is multicast need to end up somehow LAN, not the GRE tunnel endpoints. PIM can help with this too, but more configuration.

One note: they do have /routing/gmp tool that acts as a IGMP client on Mikrotik: https://help.mikrotik.com/docs/display/ ... t+Protocol
You should be able to see if the IGMP is at least making to the other end, or which end it's working, etc.

If you just got two sites, the IGMP Proxy could work too. That simple to test/try too:
https://help.mikrotik.com/docs/display/ROS/IGMP+Proxy

Amm0 · Sun Mar 10, 2024 3:06 am

Perhaps adding the gre tunnel interface as well as the LAN one may be what's missing, dunno:
/routing pimsm interface-template add instance=pimsm1 interfaces=gre1,bridge,vlan1,etc...

And the new docs on PIM-SM make a mess of things with OSPF and loopback. But using an RP might help on the PIMSM route...
https://help.mikrotik.com/docs/display/ ... thstaticRP

Now...one reason* why Mikrotik use OSPF in example is because everything has to be unicast routable...but I presume the tunnels were already routing unicast (either static routes or BGP/OSPF/RIP/etc). e.g.

It's important to ensure that each router has the correct routing information to reach the R1 loopback address.

But you should NOT need a loopback or OSPF ... as long as the PIM RP was reachable via IP routing from the other site.

*other potential reason for using OSPF in example is it's actually need for PIMSM — but they should be independent things... then again, there have been lots of reports of troubles with PIM on this forum too...

Amm0 · Sun Mar 10, 2024 3:30 am

Hold on. You're doing all those things. I didn't scroll down in your original post.

But you show this:

admin@RouterA /routing/pimsm/static-rp> print
0 instance=pimsm-instance1 group=239.10.0.0/24 address=172.1.1.1
admin@RouterB /routing/pimsm/static-rp> print
0 instance=pimsm-instance1 group=239.10.0.0/24 address=172.1.1.1

But your posting says the multicast address is 239.1.0.0/24 e.g. not 239.10.0.0/24.

Multicast audio is transmitted on 239.1.0.0/24 on Site A.

hobbes159 · Thu Mar 14, 2024 4:49 pm

Typo on my part when I was posting, I cleaned up some of the IP addresses to make it easier to follow for the post. It is set up correctly with the same multicast address in production.
I haven't had a chance to spend more time troubleshooting this... my next step was to try and set up a v6 VM at each site and see if I can get it to work on those instances, as I had read that RIP might be broken in v7 and I want to rule that out using the same setup.

Hold on. You're doing all those things. I didn't scroll down in your original post.

But you show this:

admin@RouterA /routing/pimsm/static-rp> print
0 instance=pimsm-instance1 group=239.10.0.0/24 address=172.1.1.1
admin@RouterB /routing/pimsm/static-rp> print
0 instance=pimsm-instance1 group=239.10.0.0/24 address=172.1.1.1

But your posting says the multicast address is 239.1.0.0/24 e.g. not 239.10.0.0/24.
Multicast audio is transmitted on 239.1.0.0/24 on Site A.

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