When tunnel doesn't PONG, ask to check firewall

checker/checker.go

@@ -371,6 +371,14 @@ func studentChecker(std *adlin.Student, also_check_matrix bool, offline bool) {
 		})
 		if err != nil && verbose {
 			log.Printf("%s: Unable to perform ping to %s: %s", std.Login, stdIP, err.Error())
+
+			if tunnel_version, err := minTunnelVersion(std, tun.SuffixIP); err == nil {
+				if has_test(CheckMap[tunnel_version], Firewalled) {
+					if e, err := std.GetChallengeError(CheckMap[tunnel_version][Firewalled]); err == nil && len(e.Error) > 0 {
+						std.RegisterChallengeError(CheckMap[tunnel_version][Firewalled], fmt.Errorf("Your host is unreachable, no more tests are performed. Check that you are not filtering the tunnel (Wireguard uses UDP datagrams), nor ICMPv6 as your host needs to respond to PING."))
+					}
+				}
+			}
 		}
 	}
 }