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DNS stops working on PCs in LAN

We have about 16 PCs in our office LAN that use a Netopia 3347-02 DSL modem/router for internet access (AT&T Business DSL). All PCs obtain their IP address from this router via DHCP and the router acts as the DNS server for the LAN as well. The results of the nslookup command shows the IP address of the Netopia as the DNS server. Throughout the day, all DNS lookups will suddenly fail, but the PCs can still ping the IP address of hosts on the internet. We can resolve the issue only by cycling power on the router. Once the router is powered up the name resolution begins to work again for a while.

chuku

do you have access to the router?
first thing to check would be DNS resolution on the router itself. if it can't resolve there is a local problem and you should contact your vendor (or update the router, test again and then contact the vendor)
sound like the routing is good since you do get ping replies to outside IPs

eitama

Try enabling some sort of logging on the router,
for example, make the router send logging messages in Syslog format to a PC on the LAN,
Set it to the highest level on the DNS section,
Open a syslog application on that PC, and inspect the messages.

Generate a DNS resolution, and watch the log, it may help you find the problem.

craws01

ASKER

I do have access to the router. The router can resolve no problem at all even when the PCs can't.

eitama

Ok,

Next time you have this problem, use wireshark to capture the DNS query and the subsequent http request
from a PC that is having problems, save the pcap to a file, rename it as a jpg file and post it here please.

Please provide some text, where did you try to access, and the source IP of your PC - for the pcap file.

Eitam.

ASKER CERTIFIED SOLUTION

etosan

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