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I have connected 2 Routers via OSPF (using N links, N == 1 but it should be scalable to N > 2) and I am trying to have mDNS traffic go from LAN to LAN across the OSPF link, but I can't seem to make it at all.

The routers I have (MOXA EDR 810) allow to use DVRMP and PIM-SM (or SSM). From what I read online the way to go should be to use a combination of PIM-SM, as it is designed to work with already existing unicast routing algorithms (so OSPF), and IGMP.

For the record, it could be that the quick answer is "mDNS is local only, therefore it won't be routed", but I still am trying to dig on the net to understand if it is feasible or not.

Do you have any suggestion on how to configure PIM-SM and IGMP with OSPF to multicast across the LANs?

I tried following guides from nvidia and huawei and tested multiple setups but I feel like, as I have very little experience on the matter, I could be making confusion trying to explain any of the setups I tried.

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mDNS uses a link-local multicast address (224.0.0.251) that cannot be sent off-link, so you cannot route mDNS packets.

RFC 5771:

4. Local Network Control Block (224.0.0/24)

Addresses in the Local Network Control Block are used for protocol control traffic that is not forwarded off link. Examples of this type of use include OSPFIGP All Routers (224.0.0.5) [RFC2328].

IPv4 Multicast Address Space Registry:

The range of addresses between 224.0.0.0 and 224.0.0.255, inclusive, is reserved for the use of routing protocols and other low-level topology discovery or maintenance protocols, such as gateway discovery and group membership reporting. Multicast routers should not forward any multicast datagram with destination addresses in this range, regardless of its TTL.

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