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


  • 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:

  • (Ubuntu)
  • (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

Any ideas ?


EDIT: via ping diagnostics directly on vigor, is pingable, 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.

share|improve this question
Is this access from within the internal network or externally? – user48838 Jun 29 '11 at 14:50
tried both, both stop working on unbuntu (via the external ip) the internal ip is reachable on both hosts at all time. – Rufinus Jun 29 '11 at 14:59
When the situation is occurring with the Ubuntu system, is it still reachable internally through its internal IP, but not internally through its public IP? – user48838 Jun 29 '11 at 15:26
see my last edit, from the vigor (AKA gateway) the host is no longer reachable per ping on his internal ip (!!). but from any other host in the network its normal reachable. but now the funny part, i can ping the gateway from .51 and AFTER the ping, the gateway is also able to ping .51. – Rufinus Jun 29 '11 at 15:35
Owww this is really great guys. I just run into the same Problem. EXACTLY the same system and EXACTLY the same symptoms. Tested them all. Did Draytek Support find a solution for this one? I have about 10 Servers suffering from this. Greetz I.S. – user114186 Mar 15 '12 at 13:12

Pose yourself this question first: "Is the traffic reaching the ubuntu host"

You could answer this question by doing:

  1. Log packets on ubuntu host
  2. Wait for problem to occur
  3. Look in your logs to see if packets were received prior and after the problem starts

*UPDATE OK I read your updates - does your Ubuntu machine lose connectivity? Or is it still able to ping the outside world and the LAN?

share|improve this answer
1) no its not, vigor doesnt see .51 after a while. 3) any suggestions on how to increase debug level ? – Rufinus Jun 29 '11 at 15:10
I mean look at the logs of the packets you are receiving before & after. This will help identify where the problem is. Look into using tcpdump/wireshark to do this. – SuperBOB Jun 29 '11 at 15:14
no, connection is perfectly fine from the ubuntu host. as soon as the host pings the gatway (vigor) or a ip on the internet vigor is instantly seeing .51 again. i will add a cronjob which pings the gatway every few minutes, this will solve the problem, but i cant understand why this is happening. – Rufinus Jun 29 '11 at 16:05
Almost sounds like some kind of power saving – SuperBOB Jun 30 '11 at 10:31

If the Draytek Vigor and the Ubuntu system are both directly cabled, then try disabling "Auto Negotiation" on either one of the connecting NICs. You might also take a look at the MTU settings across the path to ensure things match up as well.

share|improve this answer
all the same, and all as it should be. remember it works when the host comes up or the router is restarted, it is just like a timeout which hides the host from the gateway. i notice i can use a "keep-alive" ping from the host to the gateway this will solve the problem, but the why its happening is still in the dark – Rufinus Jun 29 '11 at 16:07
Is the Draytek Vigor and the Ubuntu system directly cabled? If so, has at least one of the NICs been taken off "Auto Negotiation" for the line settings? – user48838 Jun 29 '11 at 16:45

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