How do I troubleshoot DNS peculiarites?

I just installed a Netgear WGR614v4 54g router, latest firmware V5.0_02 pre-installed. I cloned my MAC address and connected to cable modem. I had previously been running an SMC7004WFW-802.11b router against this same cable modem. (The wireless in that one started dying occasionally, but I don't think I ever had a DNS issue.)

Both my wired desktop and Netgear WG511 54g wireless laptop are having the same DNS problem: Some sites resolve just fine, and I can ping or surf. Other sites don't resolve. some resolve, but too late for a web page. (I ping after the web fails and it's okay, and then I can surf.)

Occasionally, a site that worked fails. It seems that I can ipconfig /flushdns and then the sites all seem to work.

Something is a little snarky and I don't know where to look, exactly. tracert will tell me where routing breaks down, but if I can't resolve a hostname, how do I know where to place blame?

Windows XP - SP2 on both desktop(home) and laptop(pro). The DHCP-supplied DNS is the address of the router. I suppose I could adjust that temporarily to the address supplied to the router, but I like default setups that work ;-(

I've power cycled the cable modem and router, and rebooted the laptop and desktop. No change.

side note: handy feature on this router. It has a redirected home page so that as soon as I brought up a browser, I found myself at a router config page. I didn't have to put in the address of the router. When I finished basic config, it told me this config page wouldn't show up in the future.

On Mon, 13 Dec 2004 00:50:45 +0000 (UTC), snipped-for-privacy@XReXXHowXd.usenet.us.com spoketh

And there is absolutely nothing wrong with that. The router simply forwards the request on to one of the two DNS servers it has in its list that was received when it got it's DHCP lease from the ISP. This is an easy way of ensuring that the LAN clients doesn't have to worry about what the DNS server addresses are, or if they have changed. Since many people doesn't use dynamic addresses on their LANs, it would be a real hassle to keep up with any DNS server changes...

Lars M. Hansen

Several routers that I've worked with, including the SMC that I just replaced, and apparently, this Netgear, provide their own address as the DNS server.

That seemed to work well with the SMC, but it's not happening smoothly with the Netgear tonight. I had a Netgear 814 for a few days, and didn't notice any DNS trouble. It also referenced itself as DNS for DHCP clients.

I changed to a static definition of an outside DNS server on my laptop, and it seems to be okay. With the DHCP-provided netgear as DNS, I could ping one server in a domain, but not others, then I could, then not...

I just haven't deciphered whether it is the fault of the Netgear, or of one of the MCHSI.COM servers that are provided to the Netgear by DHCP.

I think I'll plug my stable address into the Netgear, instead of using the DHCP supplied addresses, and see what happens.

Hmmm. Maybe that's it. attbi just isn't stable for me. Plugging in the dns from my favored ISP, instead of the DHCP-supplied address into the router config gives me the router as the DNS address at my PC, but it seems to be working well.

I might change back to DHCP-supplied in the router later. Other than manually testing different addresses, I don't know what tool to use to investigate this problem.

My WGR614v4 is working fine for me with the DHCP-supplied DNS address. But I have long since given up on DNS working reliably from my ISP, and use a DNS caching program now. There are a number of freeware ones, but ExtraDNS is the best I have found, even if not free. But you have to run it as Administrator if using Win2K/XP.

Or, with XP or W2K, you can just run: ipconfig /flushdns I have this command setup as an icon on my desktop.

Other useful DNS incantations are: /flushdns Purges the DNS Resolver cache. /registerdns Refreshes all DHCP leases and re-registers DNS names /displaydns Display the contents of the DNS Resolver Cache. /showclassid Displays all the dhcp class IDs allowed for adapter. /setclassid Modifies the dhcp class id.

I just love this message: ipconfig /registerdns Registration of the DNS resource records for all adapters of this computer has been initiated. Any errors will be reported in the Event Viewer in 15 minutes.

Yawn. I get to wait 15 minutes to find out what went wrong. Sigh.

I would recommend running services.msc from the Start|Run box and observing whether or not the DNS Client service is running (likely it is). I routinely stop that service and set it to disabled - this is the client side caching dns client that caches not only good dns replies, but also caches dns lookup failures. Caching failures may not be such a smart thing to do IMHO - especially if you are using your ISP's dns servers which may be overloaded and therefore busy and unresponsive.

HTH

You can keep the DNS Client running, and just eliminate the caching of dns lookup failures by downloading the script file W2KWXPDNSfix.reg

Thanks for posting that. Disabling the negative caching is something I knew was possible via registry hacks; having it automated makes it somewhat safer.

Winner. That would explain symptoms I've seen here and at work for a long time. At work it happens infrequently, but I think I'll still whack it.

I still don't know how to pinpoint who is causing the errors. Since setting the router to use a stable DNS server, I've been fine.

Make sure that if you previously had ICS installed on the machine, that it has been removed, otherwise the DNS requests will firstly try and get DNS in this way, resulting in a timeout. Only after this has timed out will the DNS servers on your router be contacted, by which time your browser may well have timed out as well. I had this problem on a customer's machine who was complaining of big latency when trying to view any URL, which resulted in most pages not being displayed, and the ones that did were VERY slow even though they had 2Mb dsl. Removing ICS from the machine fixed the problem.

VERY slow pings are a symptom of this problem.

Hope this helps

Peter Phillips Software Director Kinetiq Networks Ltd (UK)

Then I would have been a little less tired of re-running the command last night ;-(

The closest that I can come to "troubleshooting" would be a script to drive nslookup, checking each of several name servers. But if it's a flaky server, that might not have pointed the finger well enough.

I've set the router to a static DNS server IP. The router in turn gives its own address as the DNS server to my network via DHCP. It seems to work fine today. If it fails, I presume that it will fail in solid fashion and be a little easier to track down except that I will certainly forget that I set the static address on that obscure router screen.