IPv4 only, just a local class C net... seems easy.. didn't work?


Sorry… probably is dumb. I already spent time and ready all referent to my case.

What I want to do is simple:

  1. Syncthing over a plane class C network (i.e:
  2. All my pears will be there.
  3. Only IPv4 if possible.
  4. All pears should be able to discover by itself and auto accept shares.
  5. all host has FW, that needs to be properly configured (not bi-directional allow :-)).
  6. I want only local discovery over broadcast… I don’t care noise :-).

Well seems easy… but I’m not able to make this work.

I’m running last 0.14.52v over MAC on all of them.


  1. What FW rules needs to be deployed there?. I already put what are requested from the source IP range that I’m working on over 21000 UDP and 22000 TCP…

  2. how disable IPv6. I don’t control it.

Thanks a lot

It’s 21027/udp for local discovery, see https://docs.syncthing.net/users/firewall.html#local-firewall

Also, if you do remote source port checking, you can’t predict what that will be.


Fat fingers… I actually filter for 21027/UDP … i just put it wrong here… and yes… I’m filtering on destination port… not source port.

So… no idea honestly

Meaning you never got a connection?

I think routers sometimes prohibit broadcasting (not sure whether that’s just relevant for bridging networks) - did you check that?

Also you could have a look at the logs, and if there is nothing interesting, maybe enabling the discover debug facility will yield something.

Guys… my fault. After hours… I didn’t remind that I activated 2 FW on the same MAC, one L.Snitch and the main of OS X. Configuration didn’t work and I didn’t got the point…

Once I remove the second one… all works instantly.

Thanks and sorry

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