I already had the latest firmware but it didn't seem to prevent the problem.

I've done a bit of searching and a solution I found suggested disabling DOS protection. I did this a day ago and I haven't had the problem since.

I don't want to be open to attacks though, so ideally I want DOS protection to be on. Can anyone think of any possible solutions?

TIA

from DoS disable (uncheck) only UDP flood protection & should be ok
Any way if some DoS you in real the router will fail whatever settings is in there)
But keep the other settings for scan ports etc

james.f wrote: I don't want to be open to attacks though, so ideally I want DOS protection to be on. Can anyone think of any possible solutions?

Just keep it switched off and don't worry about it.

I am having the same issue. My situation is as below:

I have 2 VigorIPPBX 2820's in the same building, separate companies, separate BT ADSL lines, separate LANs.
Both have been installed for 3+ years, no issues, rock solid performance...until about 3 weeks ago.
Since then both companies have noted the same problem.
After 2-3 days of normal operation DNS lookups will start to fail. The easy fix is to reboot the router or (better for us) just unplug the ADSL line for a minute.
Normally the PCs will use the router to resolve domain names, but nslookups to external DNS's will also fail.
It doesn't matter which external DNS is used (I've tried BT's own, Google's and others)
The strange part is during the failed state I can still succesfully ping the DNS (both from a PC and from the router itself)
It's almost as if port 53 traffic was being blocked upstream of the router but I know that wouldn't make sense.
Does anyone know of any tests I can do to show where the problem lies?

Thanks
MikeW

Mike, your issue sounds identical to the one I had. No matter what DNS server I used, I could ping it but couldn't look up anything. I did two things, and I haven't had the problem for 2 weeks now.

I disabled the DoS protection, though I don't want this to be the permanent solution so I'm still on the lookout for an alternative.

Also I implemented a session limit of 200 on visitors' IP addresses. All wired PCs and staff wireless devices have a fixed IP which has no session limit. Anything else that connects to the Wifi will have session limit imposed on it. I wondered if too many sessions were choking the connection. Again, in the long run, a workaround would be preferable.

Let me know how you get on and if you find a solution.

Hi James

Thanks for the response.

In this situation there is no wi-fi, and only 6 to 8 hard wired clients connecting to each router, and minimal internet traffic.
I will try disabling DoS and monitor the connection counts in case anything nasty got onto our network but it's unlikely.

Cheers
MikeW