I know this is a kinda unusal question, but Draytek support (..which is very eager to solve the issue) seems to reach its limits.

Scenario:

• Draytek Vigor Multiwan router with current firmware.
• Multiple WAN IP Aliases on one of the wan ports
• DMZ (or port forwarding doesnt matter) from wan ip alias to internal host

currently i have two internal hosts:

• 192.168.0.51 (Ubuntu)
• 192.168.0.53 (Debian)

both should be accessible from outside via one of the wan ip aliases.

both are accessible with their internal ip's at all times (!)

If the router gots restartet, both external ips are forwarding to its internal hosts. But after a few minutes up to 2 hours, the ubuntu host is no longer reachable via its external interface. The debian hosts on the other hand is reachable.

In what does ubuntu differs from debian ?

I know at least of one user with the exact same problem. see http://ubuntuforums.org/showthread.php?p=10994279

Any ideas ?

TIA

EDIT: via ping diagnostics directly on vigor, 192.168.0.53 is pingable, 192.168.0.51 is not.

but both hosts are perfectly reachable from anywhere inside the network.

if i restart ubuntu networking it works again for a short time.... i'm out of ideas..

EDIT 2: after further investigation, i noticed a ping from .51 to the network (or a host in the internet) is enough to make the port-forwarding working again. So i will add an Cronjob as a "keep-alive" ping. This will solve the problem, but the reason for this behaivor is still in the dark.

Thanks to all commentors.