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No DNS Resolution

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by pozotech

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Have NT 4 network (sp6a) have 1 pdc and 2 bdcs. Have exch 5.5 sp4 server, proxy 2.0 (w2k) and web server (w2k sp1) that all have dual nics. Am connected to full T-1 that comes in through a Ascend Pipeline 130 router. In the last day I have lost the ability to resolve outbound dns names. Our provider has tested the inbound T-1 and all is working to the nic in the servers. I can ping out by ip number but when I try to ping www.name.com I get either a time out or bad ip address response. From the outside my web server works fine. All inbound and outbound email has stopped. Any thing I have missed aside from changing out the router? Thanks Jeff

10 replies

by cavedweller

I would open a command window on your server and try nslookup interactively. Use the "set all" command to view your current settings. Enter a query and see what the error response is. You will be able to verify if your "parent" dns server is responding. You can also temporarily change some of the dns settings and see if it makes an improvement.

by pozotech

When I try nslookup I get the message dns time out. Can't find server name for address. Default Server - unknown. When using set all - what should I see? Is the root= line to have to name of my DNS server? It does not.

by 4u21der

Quick 2 cents:

Your SOA records are pointing to a host named ns1.fix.net and ns2.fix.net! If these DNS servers are local to you then i would check your forwareder records and see where the are pointing and if they are forwarding and resolving replies from "Upstream" DNS servers.

You also did'nt mention if you are running DNS on your W2K box. This can make a big difference.

Try to also perform a nslookup from OUTSIDE your proxy server. Is your Proxy server doing packet filtering? If so, make sure it is passing TCP and UDP port 53 traffic.

I also do not see a MX record for fix.net, if this is your domain and you are the SOA for that domain you need to add that record or ask your ISP to assist you with this.

There is also a great tool that allows you to do more detailed DNS searches and is a bit more user friendly than "nslookup".

If you would like a copy please send me an email and i will send you a copy.

Hope my 2 cents was helpful and not harmful

Good Luck!

by pozotech

Thanks for the info - with our mail server down - the soa and dns info you refered to is my personal account. The info on the Port is what i need . I had turned filtering on - on all machines.

by cavedweller

If you get a timeout it usually means one of two things, either the dns server (and any named backups are down)or you can't communicate with them. You can try to ping them to verify a connection but most servers are set not to respond. You might try telnet or ftp but a secure site is likely to reject these too. Make sure that your proxy server allows dns traffic (port 53) to pass.

The root server is who to query when all else fails and should not be set to your own address except in certain cases where your network is completely isolated.

Call your provider and verify that there dns server hasn't changed address (it probably hasn't).

by pozotech

Thanks for the info - filtering was the answer. I had changed it and reboot made the change effecitive - made the change a couple of months ago - never rebooted. Does dns traffic require port 53 on TCP and UDP?

by stillatit

Either your proxy server is blocking DNS traffic or you are pointing at a bad DNS server.

1. Look at the proxy server, and see if its filtering is on. If it is, turn it off for a moment and see if you can now do DNS lookups. (You may have to restart Proxy server after making the change.) If you can, you need to add a filter allowing DNS traffic to go through the proxy server. Turn filtering back on when you are finished, and test.

2. On the proxy server, check the tcp/ip properties for the dns server in use. Pick another dns server (ask your isp for a number), and replace the old numbers with the new number. Then test DNS lookups. (If you cannot get a number, try using 64.77.55.65 - that is PacBell's name server.) If this works, you need to get a good list of DNS servers from your ISP, and plug these into all stations.

Good luck.

by stillatit

It also might be the case that filtering in the Pipeline 130 got turned on, and is blocking DNS. Telnet into the pipeline and check its filtering.

by pozotech

You #1 answer really got me going in the right direction. Turning the filtering off - and a reboot got the Proxy up and running - had to do the same on the mail server. Really appreciate you help.

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