Does Avahi work over a bridged network?

I have a network set up something like the following:

Device A <---> Router A <---> Router B <---> Device B

where Router A is a tp-link Archer AX73, and Router B is a tp-link Archer C7. Router B is flashed with OpenWRT, and Router A is using stock firmware. Router B is set up to be a wireless bridge between Router A's network, and its own (it was set up using this guide).

What I am wondering is if Device A can find, say, Device B.local, using Avahi (assuming Device A, and Device B both have Avahi installed, and running), over this bridged network. So far, I haven't been able to get it to work, so I'm wondering if it is possible at all. I have read that Avahi only works on a local network, but I was wondering if it could be bridged.

UPDATE (2024-01-16T01:28Z):

The issues that I mentioned in this post have since been solved. The majority of the issues stemmed from the fact that the relay software that I was using, relayd, doesn't support ipv6. All the tests that I was conducting were defaulting to ipv6, so it was appearing like the bridge was failing unpredictably. Since that realization was made, and countermeasures were enacted, the problem was solved.

eutampieri ,

These are routed networks, and you need avahi reflector set up to mirror between A and PtP and between B and PtP

Kalcifer OP ,
@Kalcifer@sh.itjust.works avatar

Router B is bridging Device B to Router A's network, so they aren't on separate vlans; thus, it shouldn't require an mDNS reflector as that repeats mDNS between separate subnets.

eutampieri ,

Then I don’t understand your topology.
However, I still think you need the reflector on both routers

Kalcifer OP ,
@Kalcifer@sh.itjust.works avatar

Afaik, an mDNS reflector is only needed to cross subnets -- both subnets and mDNS function on layer 3. Bridging occurs on layer 2, and since mDNS functions in layer 3 (ipv4 multicast is layer 3), the bridge itself is invisible to it.

eutampieri ,

This works if B has an interface that is connected to the A subnet, but not if you have a PtP between the two routers

Kalcifer OP ,
@Kalcifer@sh.itjust.works avatar

This works if B has an interface that is connected to the A subnet

I'm not sure I understand exactly what you mean. Is it not given that if two routers are connected to each other then an interface from either of them will be connected to the other?

but not if you have a PtP between the two routers

What do you mean by PtP? Are you referring to something like WDS, or, in my case, relayd?

eutampieri ,

No, with PtP I meant a point to point link on a dedicated interface just for the two routers.
https://image2.slideserve.com/5192070/point-to-point-sub-interfaces-l.jpg

Kalcifer OP ,
@Kalcifer@sh.itjust.works avatar

Wait, are you just generally referring to this? That already exists in the form of PPPoE, and, for all intents and purposes, WPA, does it not?

eutampieri ,

No, not at all 🙂. I'm referring to a configuration in which the two routers are linked through another subnet (using a separate link between the two) and this link is the point to point link. You usually assign a /30 so you can have an address for each router.
This way the traceroute shows three hops instead of just two.
However, since you’ve already told us that this is not your setup, what I’m saying shouldn’t matter to you. If you’re curious though, let’s keep talking :)

Edit: striked mistake

Kalcifer OP ,
@Kalcifer@sh.itjust.works avatar

Interesting, where does the 3rd hop come from? Wouldn't the routing table just point from one router to the other -- so 2 hops?

eutampieri ,

Traceroute from device in subnet A to device in subnet B

  • Router A
  • Router B
  • Device B

Note that the only way to do that in only two hops is to have the same router handle both subnets, contrary to what I said earlier.

Kalcifer OP ,
@Kalcifer@sh.itjust.works avatar

To make sure that I understand correctly, are you describing something similar to what was described in this thread?

eutampieri ,

Hmmm it seems that router B there should be a bridge. However, how comfortable are you with routing in general?

Kalcifer OP ,
@Kalcifer@sh.itjust.works avatar

However, how comfortable are you with routing in general?

Ha, depends what you mean by that. If you mean manually specifying routes in a router, I think I generally understand it, but I am not at all confident in my abilities.

eutampieri ,

Exactly that.
Router A

ip address add 192.168.1.1/24 dev eth1
ip address add 10.0.0.1/30 dev eth2
ip route add 192.168.2.0/24 via 10.0.0.2

Router B

ip address add 192.168.2.1/24 dev eth1
ip address add 10.0.0.2/30 dev eth2
ip route add 192.168.1.0/24 via 10.0.0.1

Does this make it more clear?

Kalcifer OP ,
@Kalcifer@sh.itjust.works avatar

Does this make it more clear?

Yes, thank you! Usually, however, most of my issues seem to stem from knowing where configs are, what tools to use for what, or where to find things in the router user interface, etc.

eutampieri ,

I definitely agree!

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