I have been using a TP-Link Router in front of IPFire for several years know without having any problems. Last week I exchanged the TP-Link Router through a Fritz.Box 7520. Since then I cannot update IPFire anymore via pakfire (HTTP-Status-Error 500 / Name or service not known) and a sync with the time servers (NTP) is not possible as well.
I really would appreciate it if someone is able to help me.
your hint worked well for me. After changing the protocol from UDP to TLS the IPFire made the update. Really seems to be a strange behaviour of the Fritz.Box