I confirm the same: computers in NASK ISP are visible fr om computers in NASK always, and fr om those in Orange sometimes, with breaks (the icon of the RU host becomes grey temporally). Computers in Orange are never visible from anywhere. Pinging etc. to id.remoteutilities.com gives very good results, cited by Mateusz.
Is there any kind of test we can make from here to make sure wh ere the problem is? Orange will send the problem back as soon as they check the access to your servers. Generally, I have had very few if any problems with Orange, the company owned by France Telecom. Until now.
The two computers which were invisible (appeared offline) were in Orange - physically, or in NASK (National Academic Computer Network) - through VPN. In both configurations they were invisible to other computers, but the other computers were visible from them. The two computers which were both visible (online) and could be accessed were physically in NASK. As I wrote, the ping and tracert to your DNS server worked fine from all.
But, finally, today it is all OK with my computers. I wonder what has been changed.
A similar problem occurred to that described in this thread. Now, there are no problems with ping or tracert to id.remoteutilities.com and the host which are offline stay offline even if I switch them to another domain by VPN (to a domain in which the online hosts are). Other users in Poland experience the same.
If anyone else in Poland connecting through Orange has this problem, please report it to Orange. I did, in fact twice.
The main issue is that >ping id.remoteutilities.com returns "Request timed out", although the IP address of this DNS server is found properly. With tracert it can be readily seen that the packets get stuck somewhere on the way.
BTW, the IP of id.remote.. is 188.8.131.52. The last server in tracert for this IP is 184.108.40.206, an Orange server. Both these addresses are listed as blacklisted by dnsbl.spfbl.net . Interesting.
The same problem appears. Since yesterday, all my four hosts mutually appear offline.
As we are now asked to work from home (COVID), the connections became urgently needed.
Two computers are now in my place and they appear offline mutually. I tried to connect both by two different methods (internet by optical fibre+WiFi, internet by mobile phone hotspot, both from same provider). I have checked all indications according to the chapter Cannot connect using Internet-ID connection and both sides fulfil all the conditions listed there. No settings were changed anywhere in the internet connections around in the meantime.
In the host as well as the server logs it can be seen that both connect and disconnect in short intervals. Below are fragments of both: