What Does "search Lan" Mean When Using Vpn?


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I am using BTSync with devices that connect to each other with a VPN. So they each have an IP address on the local LAN (where they are alone) and also an IP on the VPN. When I check "Search LAN" will it search both? Or just the local LAN? Obviously, my preference would be for BTSync to work over the VPN.

 

When it is "searching", is each client sending a broadcast and waiting for a response? Or just listening for a broadcast?

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It depends on how the routing is. If your VPN is routing everything through VPN then discovery of other peers as well as data transfer will go through VPN. But even if VPN is off on all clients but have access to the internet they will be able to find each other and transfer data. Although that statement depends on how your network access is.. if you can't due to firewall rules etc then this is obvious that it is not working.

 

And search LAN will mean that BitTorrent Sync is looking in it's own subnet for other peers that have BitTorrent Sync running. So there's that. Please correct me if I am wrong on this one.

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@Moe, @Shaav

Its a bit more here. Sync is sending multicast packets for other peers discovery with TTL=3. So it actually depends on a router how to behave. If router is simple and is not aware of multicast - it will just route packet and decrease TTL.

If it is aware, then multicast with TTL=3 will be routed within same organization / site. So it more depends on VPN gateway implementation.

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@Moe, @Shaav

Its a bit more here. Sync is sending multicast packets for other peers discovery with TTL=3. So it actually depends on a router how to behave. If router is simple and is not aware of multicast - it will just route packet and decrease TTL.

If it is aware, then multicast with TTL=3 will be routed within same organization / site. So it more depends on VPN gateway implementation.

 

Thanks @RomanZ --- this is kind of an unusual case and I'm using VPN because I don't have direct access to the networks in question (except 1 --- not the one I'm particularly interested in. :) ). So I don't have any idea what the routers or their configurations are like for 3/4 devices that are syncing.

 

I've been experimenting quite a bit and the peers do not seem to find each other on the VPN. I.e. if I turn off relays/tracking/DHT and just leave searching the LAN, they do not find each other. But more surprising, EVEN when I provide explicit VPN IPs and ports for the peers, they won't find each other and won't sync until I turn on using the tracker.  Any thoughts on that?

 

They definitely are accessible to each other through the VPN. I ssh into one and then can ssh into the others without any difficulties (for instance).

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@Shaav

I suggest trying to enter predefined hosts to folder properties. The IP:port pair should point to the peer behind VPN gateway, i.e. use not a gateway IP, but IP you would use to reach remote peer. See if it works.

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@Shaav

I suggest trying to enter predefined hosts to folder properties. The IP:port pair should point to the peer behind VPN gateway, i.e. use not a gateway IP, but IP you would use to reach remote peer. See if it works.

@Romanz

That is what I mean I did when I said "EVEN when I provide explicit VPN IPs and ports for the peers". Does not work.

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@Shaav

That should actually work. It directs Sync explicitly to connect to a designated IP over UDP/TCP. I wonder if you can do the same test with NetCat utility: open a UDP socket for listening behind VPN and try to connect to it from PC which connects to VPN network.

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