I've been running syncthing for a while now on a NAS (Asustor), a PC (Linux Manjaro) and a netbook (also Linux Manjaro).
The netbook and the NAS are connected to the same router, so that's one network. But I have not set them up to sync. The PC is connected to a different router in a different network, and I have synced with both the netbook and the NAS. Since the NAS is supposed to act as a kind of backup, it has to copy all the data from the PC, which is roughly 5.5 mio files and 2.3 TB data. It took already about a week, when all of a sudden the NAS was reported not to be connected to the PC. However, the PC could connect to the netbook, which makes me rule out a router problem.
I thought it over what I could have done, and remember only one thing that I did on the NAS:
since there were a number of illegal attempts to log in to the NAS via ssh, I checked the list of IP adresses which tried to log in and put them all on a black list. Now I wonder if I mistakenly took one or more IP-address(es) which belong(s) to the syncthing relays, thus making it difficult or impossible for the two to connect any longer.
Would this be a possible szenario?
I'm not eager to go through the list of IP-addresses, it would take a lot of time. So first I would like to know if this is a possibility. If not, I am of course open for alternative suggestions.
One more thing: When I ran
STTRACE=discover syncthing I get the following (among others which do not seem to be serious porblems):
[5STJK] 2017/07/08 15:06:12.716990 global.go:147: DEBUG: globalClient.Lookup https://discovery-v4-2.syncthing.net/v2/?device=... 404 Not Found
[5STJK] 2017/07/08 15:06:13.111165 global.go:147: DEBUG: globalClient.Lookup https://discovery-v4-3.syncthing.net/v2/?device=... 404 Not Found
[5STJK] 2017/07/08 15:06:13.184057 global.go:147: DEBUG: globalClient.Lookup https://discovery-v4-4.syncthing.net/v2/?device=... 404 Not Found
[5STJK] 2017/07/08 15:06:13.236365 global.go:142: DEBUG: globalClient.Lookup https://discovery-v6-2.syncthing.net/v2/?device=... Get https://discovery-v6-2.syncthing.net/v2/?device=...: dial tcp [2604:a880:800:10::182:a001]:443: connect: network is unreachable
(I replaced the device-ID with "...") Does the above give any clue?