LAN DNS dropouts on BT 2wire BT2700HGV router

I'm working on a mixed Mac/PC LAN of around 10 users all connected to a 2wire BT2700HGV router. The router is set up as the DNS server. There are no servers in the office. Some are connected via ethernet, others by wifi.

They've had this problem before and it magically seemed to go away but now it's back.

When the issue does manifest itself, seemingly randomly, 3 or 4 times a day DNS will drop out completely for anything up to 20 mins at a time, not just to internet traffic but between internal machines too. Sometimes, this affects just one PC, other times several or even the while office. It doesn't seem to occur at obvious times like someone switching their PC on.

pinging IP addresses is always fine regardless of internal/external destinations. DNS resolution for both internal and external destinations fail for both when there is an issue.

There are two ADSL lines to the office with identical Routers. switching them over makes no difference (I've made sure that the two networks are not connected in any way).

Other things I've tried but don't seem to fix...

* Using static IPs on all machines.

* Used BT's DNS nameservers on the router
* Used OpenDNS DNS nameservers on the router
* Used Google's DNS nameservers on the router

* Used BT's DNS nameservers on each machine
* Used OpenDNS DNS nameservers on each machine
* Used Google's DNS nameservers on each machine

* Followed all the advice in http://installingcats.com/tag/slow-dns-lookup/#direc... (so made sure DNS entries are reversed when appropriate)

* flushed all DNS caches on all machines and then reboot router

* made sure IPv6 is disabled on all machines.

Called BT and they bascially won't help until I can prove it's either a router or a line problem and to do that their only suggestion is to run the network with only one pc. The trouble is, the problem doesn't even happen every day (or even week), just that when it does, it's can take hours or days to sort itself out.

Any ideas what could be causing such random problems? Does the BT2700HGV router have a history of similar issues?

Normally I'd consider myself half decent at networking and have set-up/managed dozens of PC networks but I've never come across anything like this on a server based network or any small (home) peer network.

Is the router beefy enough to cope with a peer network of 10 users? They're all on Gmail / Google Docs but there's no massive file up/downloading going on. To tell the truth, I'm feeling a bit lost without server logs and diag tools and I'm secretly hoping this particular companies love of 'cloud based' services will diminish so I can sort them out with a proper server.

I'm considering sacrificing a few chickens as the next option as I've completly run out of useful ideas.

I'm having the same issue with the same unit on bt broadband (using Bt Business Hub, 2 wire etc etc). We're not running a complex network, there's only 4 pc's and they're all plugged into the router. Broadband speed itself is fast on an online speed test (12mbps), but it can 30seconds to a minute to connect, and sometimes just wont connect to a new website for about 5 or 6 attempts with about 1-5 minutes between attempts.

At time's i've unplugged all the ethernets, and used it with one laptop overwireless, often getting the same treatment, ergo the it does the same thing with a one pc set up.

I'm going to look at the article in your post, and try that, if you've had any breakthroughs please let me know,

Dave

It turned out to be that the users were using too many network sessions and were overloading the router.

We were using iplayer, Skype and a lot of cloud based chat services. This caused the router to max out in network sessions. The BT routers are configured to allow 1024 network sessions. In our case, we were averaging around 150 available connections and often spiked to hit the max.

If you're using a lot of p2p programs, Skype or anything that needs a lot of sessions to work properly, then you probably need to either make modifications to your software to use up less sessions or do as we did and buy a new router.

If you log in to the router, there's a diagnostic page somewhere that can show you all your network sessions. If you have less than 200 available sessions on an average day, then this could be your problem. There should be a long list of sessions. You can identify the PC(s) causing the most issues by IP address. This router seems to take quite some time to clear 'dead' sessions so it might take several minutes before sessions start clearing if you turn a PC off for example.

I'm afraid we don't have that router anymore and I can't remember exactly where I found the page in the menus but if the ROM version is the same as ours, try http://192.168.1.254/xslt?PAGE=C_5_5 or http://192.168.1.254/xslt?PAGE=C_3_2.

You might want to turn off Openzone if you have it on. Someone from outside might be sucking up all your sessions.

In the end we bought a Billion BiPAC 7300N router. A bit expensive but we've had absolutlely no problems since.

thanks very much for the info dale, highly appreciate it