Since the early hours of today, the free dynamic DNS service is not running properly. Updates of ip addresses that get sent to DynDNS succeed but in the end, the DNS servers do send out old information.
See more about this topic at heise.de.
How IPFire is affected
This affects some installations of IPFire, which are not able to start VPN tunnels. OpenVPN clients are not able to connect as well. And if you try to access your box from the remote site, there will be no way.
IPSec needs a working DNS to auhorize that the request for building the tunnel comes from the right machine. If it cannot verify this information, there will be no way to bring it up.
Fix the IPSec VPN problem
There is a workaround available that you can bring up the ipsec vpn tunnels immediately. For that it is required, that you have hostnames and ip addresses from both sides of the tunnel and just put both into the local DNS resolver. This can easily be done on the IPFire web interface.
After that is done, you need to restart the tunnel and you are done!
When DynDNS works again, you need to remove those entries.
Update: DynDNS reports that the problems should be fixed, now.