Because I downgraded my ADSL subscription from comfort to standard, I had to
reconfigure the modem. What I did not realize was that this
reconfiguration somehow erased all the port-address translations in the
modem. As a result of this problem, all services on the site were
unreachable from Friday evening 4th March to Sunday evening 6th March.
The server now regularly reconfigures the modem with the precise PAT settings so that this problem cannot occur anymore.