Cisco VPN client stops DNS working on LAN

[Adwoodsy]

Hi all
I'm hoping you clever people out there can help me out with a strange problem because I'm stumped!
I use Cisco VPN client to connect to another site and everything works fine for a while. After about 10 or 15 minutes DNS stops working on our LAN ... for all PC's! (There are only 4 of us)
IP connectivity still works, ie, we can ping external IP addresses, eg, 8.8.8.8, so routing is still working but we can't resolve any websites.
A quick reboot of the modem makes everything work again.

We have a BT modem connected to a Draytek 2830 router.

Anyone have any ideas what might be causing this?
This doesn't happen to me at home so I'm guessing it's either something to do with the kit at the office or the connection with our ISP?

Thanks in advance

 

[skillyho]

What does nslookup say when you try on the clients when everything fails? You can access websites by IP without incident on the affected machines, just not by hostnames? Do you have a DNS server in house? How are DNS entries being pushed to the clients (DHCP on your Router or as a service on a server?)

 

[tnt118]

I'm wondering if I have the same problem. (And sorry, no answer here...)

A couple of weeks ago my connection started dropping between 1-3 times per day. Oddly, a Roku continued to work but 2 PC's and 2 cell phones stopped. I figured something with the router was dying but never checked if it as a DNS issue. That roughly coincides with when I started using Cisco to VPN into work.

 

[tnt118]

What does nslookup say when you try on the clients when everything fails? You can access websites by IP without incident on the affected machines, just not by hostnames? Do you have a DNS server in house? How are DNS entries being pushed to the clients (DHCP on your Router or as a service on a server?)

I'll reply to this as it looks to be the same problem.

I didn't try nslookup, but yes, websites can be accessed from IP but not by hostname. The browser gets stuck on "resolving hostname" (no surprise) when trying.

DNS comes from the ISP, and the router is DHCP.

It's worth noting that Cisco VPN isn't actually running when these outages happen, but it drops 2-3 times per day. Something changed in the configuration perhaps? Or something is flooding the router to the point some part of it stops working?

I'll try using Google DNS the next time it happens and see if that helps, barring that I'll uninstall the VPN to try that. (Although if it's a configuration change, and not the program being active, that may not actually help).