DNS problems

[haxx77]

My network has 80 nodes through a T1 with a cisco 2600. Our DNS is through the ISP. I have noticed that sometimes a computer cant see the DNS server for a few minutes. The connection will be there, then it is lost only for a few minutes. Then it comes back on and resumes. This can happen on any computer on the network. I can still see the DNS from other computers while this is happening. This problem isn't isolated to any one machine. Is there a limitation for nodes that can access the DNS at one time from a given network? or is the DNS overloaded?

 

[jeter]

Have you added a secondary DNS on the router? Give that a try if you have not. Jeter@LasVegas.com
J.Fisher CCNA

 

[iggystar]

Personally, I've encountered no end of stupidity when dealing with ISPs so who knows what they could be doing to you. Next time that it happens I would get a traceroute from a machine that works and from a machine that doesn't work and compare. Who knows how their connection is setup and it's very possible that even on the same T1 you'getting routed differently. Its probably not likely but it's easy to check.

Another good thing about traceroutes is that it's something concrete you can attact to an e-mail to get the ISP working. Even if they don't really help you can use them as a stick to beat your ISP. Even if they both reach the DNS box still send the e-mail and ask them simply why their box isn't responding to you.

If you have a simple straight forward network then I dont really see how this could be your problem. It's almost certainly your ISP.

 

[hibit]

Next time it happens also use nslookup.


look and store the dns that it tries. Some isp use load balancing on the DNS and this can be a problem. If nslookup times out then the DNS might be overloaded. Try to start a ping and if you get a NSLOOKUP timeout yet no drops in the ping I would say the issue is the DNS on the ISP.