If peers in a different network (not in your LAN) try to connect, but do not show up on Peer List window, there may be a few things happening that are preventing the peers from connecting.
- Unable to reach https://config.resilio.com/sync.conf. Sync learns addresses of tracker and relay server from this sync.conf file. Check the file's availability with wget and try downloading it using a browser.
- Blocked tracker server. Once Sync learns addresses of tracker, it tries to connect to it to learn addresses of other peers. Check that connection to tracker is allowed and that "Use tracker" option is enabled in Sync settings.
If for a reason it's not possible, use option "Predefines hosts" and put there the address of a remote peer. Do that on all peers.
- Listening port of Sync may also be blocked. Once Sync knows addresses of other peers, it tries to connect to them directly and establish UDP or TCP tunnel on given IP:port <-> IP:port. Make sure that tunnel is actually possible in your network. Open Sync's listening port in your router and all possible firewalls in the way. Recheck traffic routing rules especially if multiple NIC are involved.
- Blocked relay server. If direct connection is not possible, Sync will try to establish indirect relayed connection. For that connection to relay server shall be possible for all peers.
- Using proxy. Troubleshooting will be the same as above, with proxy server involved.
If peers are in the same network and you are trying to connect devices over your LAN, these may be causing the problem:
- Multicast packets are not allowed in the network. It might be especially the case if peers are on different subnets, VPN.
Make sure that your firewall is not blocking UDP packets coming to port 3838.
- Direct multicast is disabled in router settings
Check your router settings. Some of routers have features that allow to map multicast to unicast or simply block multicast packets. These settings might be absent at all or might look different depending on router model.
- A computer may have multiple Network Identification Cards (NICs). Switching to the second network card may help resolve this.
Still having problems with connection? Please collect debug logs from two peers that cannot connect and send them to support!