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I've had problems running OSPF over my WiFi network, and it seems to be related to multicast. The routers can't maintain a neighbor relationship, and when I watch the packet traffic I see one router sending multicast Hellos to 224.0.0.5 but the other OSPF speaker is not receiving them.

The OSPF speakers are all Ubuntu Linux machines (either Ubuntu 18 or 20) running Quagga. The AP is a Verizon Fios G1100.

I'm pretty sure there's a bug somewhere, but I'm not sure where. Since there's no true broadcast or multicast over WiFi, the AP has to relay the multicast frames. Should it do this automatically? Or should the OSPF speakers announce their interest in 224.0.0.5 via IGMP?

Incidentally, adding a neighbor statement to the Quagga configuration doesn't seem to help. I resolved the problem by switching to RIP.

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    "Since there's no true broadcast or multicast over WiFi" That is not true. Multicast and broadcast on Wi-Fi can work, but it requires the slowest possible speed in order to reach distant hosts. Unfortunately, your WAP is an off-topic consumer-grade device, and your router manufacturer does not offer optional, paid support, which is required for devices here. You could always set up OSPF to use unicast and neighbor statements, but wireless can still be problematic. – Ron Maupin Jul 17 at 19:37
  • @RonMaupin aren't the WiFi packets encrypted so that only the AP can decode them? – Brent Baccala Jul 17 at 19:39
  • @RonMaupin, also, would you mind actually answering the question I asked before closing the question? Should OSPF speakers announce their interest in multicast addresses via IGMP or not? – Brent Baccala Jul 17 at 19:41
  • The WAP gets the broadcast or multicast and then sends it to all hosts on the LAN (really no different than an ethernet switch getting the broadcast or multicast and sending it to all interfaces) at the slowest possible speed. Some WAPs can be configured to replicate, via unicast to each host, but that can greatly slow things, too, since it needs to send a frame for each attached host, rather than one broadcast or multicast frame. – Ron Maupin Jul 17 at 19:42
  • IGMP plays no part in multicasts for the Local Network Control Block of multicast. IGMP is for multicast routing, and multicast addresses in that block cannot be routed. IGMP is a protocol for a host to communicate with a multicast router. – Ron Maupin Jul 17 at 19:44