At this time of writing:
- I can resolve the domain name to 91.231.175.100. That address does not respond to pings from here, I cannot establish a TCP connection to port 443, nor port 80, and traceroute(8) ends at 212.73.205.50, which resolves to INTERMEDIAS.edge3.Paris1.Level3.net.
- https://downforeveryoneorjustme.com/apec.fr says that the server is up, the problem is just me.
- https://tools.keycdn.com/traceroute testing shows failures to reach the server from 14 locations around the world -- including Paris.
My assumption is the server or its bastion network is using a packet filter, and it happens to use an OS fingerprint filter. PF can do this too, see /etc/pf.os and pf.os(5)