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DNS Problems nslookup failing

By scottf ·
I am having DNS problems on my network. Everything seems to be working correctly but we are having several RPC errors on our network between the Aspen tech server and its clients. We spoke with the Aspen tech folks and they had us run the "nslookup"command utility and the response we got is as follows: Can't find server name for address 10.0.1.254: Timed out.
Default servers are not available
Default Server: UnKnown
Address: 10.0.1.254
I am not sure how long we have had this problem because it does not seem to affect the way our network functions until now. Nothing has changed to make this happen and everything worked until yesterday around 3:30pm 5 Mar 2002. The Aspen tech folks suggested that the problem is in the DNS server reverselookup Zone. I have looked at that and I cannot tell if this is the problem or not. I can ping the DNS server and the Internet DNS servers by IP address and by name.
Thanks,
Scott

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DNS Problems nslookup failing

by mshavrov In reply to DNS Problems nslookup fai ...

Hi!. It looks like you don't have DNS properly configured. If it's UNIX - check that you have name servers in /etc/resolv.conf file. If it's Windows NT - use "ipconfig /all" to check that your DNS Server configuration is correct. Try to use "nslookup" on another computer(s) to check if it's problem with DNS Server itself. It means nothing that you can "ping" server, service may be down or corrupted. Try to use small steps to isolate a problem and you will find solution fast.

Good luck.

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DNS Problems nslookup failing

by Shanghai Sam In reply to DNS Problems nslookup fai ...

Thanks for the answer. The IP settings on the DNS server are correct. Also, nslookup does fail. As a matter of a fact the below answer#2 hit the nail on the head. BeerMonster described the problems to a T.
Thanks,
Scott

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DNS Problems nslookup failing

by BeerMonster In reply to DNS Problems nslookup fai ...

Hi,
This isn't really a problem.
When you perform an nslookup on any IP address, the nslookup util will (for reasons best known to microsoft) attempt to first resolve the ip address of your dns server to a name, and display that name as partof the output. lets say that your dns server is 10.20.30.1 and you want to do an nslookup on myserver.mydomain.com , nslookup will query the REVERSE lookup zone on your dns server to try and resolve your dns server's IP to its hostname. If it can't,you will see the output that you describe, as well as the results for the query on
myserver.mydomain.com. It's basically saying 'I can't resolve the ip address of your default dns server to a hostname, the default server is unknown'. It will then however go on to communicate with the dns server to resolve your myserver.mydomain.com query. This happens when you don't set up reverse address resolution in dns, which in most cases isn't needed anyway. What's important is that the correct IP address is returned by the query for the hostname that you are querying on, if it is then dns is working okay.

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DNS Problems nslookup failing

by Shanghai Sam In reply to DNS Problems nslookup fai ...

This is the problem exactly! This answer does help me but I don't want to close the question yet! Thanks!

The correct address is returned by the query on the hostname. To make this work correctly I need to configure a new reverse address resolution zone? I have the default reverse lookup zone configured and there is a pointer for each machine on my LAN under that folder. The only reason we started looking into this is because our Aspen Tech software began failing (nothing has changed on theLAN) it began giving the Aspen Tech clients RPC errors. The technical folks at Aspen suggested we run the "nslookup" command line utility and one the reply came back: "Default servers not available" they said the software failed because the machine could not see the DNS server. Even though that machine is able to access the Internet with FQDNs. Anyway, thanks for the help. Any tips on created or working with the reverse lookup resolution. Aspen will not help me until I get a postive "nslookup" reply.
Thanks,
Scott

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DNS Problems nslookup failing

by BeerMonster In reply to DNS Problems nslookup fai ...

Right...
It seems to me that you are chasing a dead end with the dns approach. Without looking at your dns setup I can't begin to pinpoint why the reverse resolution isn't working, BUT as you must by now realise that is unrelated to your rpc problems - UNLESS at the time you get the rpc errors you are also unable to resolve the target servers name from the problem workstation. Somewhere in the problem app there will be a reference to the remote 'aspen' server that it is connecting to either in the registry, a config file or (with sloppy coding) hardcoded into the app. If, on the client machine/s you can ping that server by name AS IT APPEARS IN THE CONFIG OR REGISTRY (IE without having to append an fqdn onto it if one is not specified) then name resolution is NOT the problem - especially if the errors are intermittent and when they are happening name resolution is tested and functions correctly fron the machine showing the error. Also, if these Asspen (misspelling intentional) guys are saying otherwise then they have a skills problem and may well not be of much use anyway. In situations like these you MUST hold your ground and make them explain why, if name resolution otherwise works, they suspect dns to be the problem. It may well be that they have no idea what the problem is and are just trying to force it back on you. RPC errors are often caused by slow networks (IE timeouts), but can also be caused by new or misconfiguered firewalls etc. Typically, unless a specific port has been specified, a client will connect on port 135 to query which dedicated port the required service \ app is running on, and will then connect to that port.

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DNS Problems nslookup failing

by BeerMonster In reply to DNS Problems nslookup fai ...

Unless otherwise config'ed that dedicated port can be anyware in the range of 1025 - 65000. If anywhere between them and you a firewall is blocking ports then that could be the problem - although that would mean a continuous not intermittent problem. Microsoft have published a number of articles about RPC errors. I would suggest going to microsoft.com/technet and searching for the keywords 'RPC' and 'Troubleshoot' . Good luck....

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DNS Problems nslookup failing

by BeerMonster In reply to DNS Problems nslookup fai ...

A final point to clarify, when I say without appending an fqdn onto the name I mean that you can ping the target just as it appears in the config or registry, as that will be how the app tries to contact it - obviously if there is a domain name already appended to it in the config \ registry (which unless you have additional domain suffixes listed in the tcpip config on the workstation there should be) then include it in the ping. You could also **** the asspen guys out of the water by using a host file (just as a test) to see if the problem goes away, that takes dns out of the loop altogether.

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DNS Problems nslookup failing

by BeerMonster In reply to DNS Problems nslookup fai ...

one final, final point (these asspen guys have really pi##ed me off). This is an extract from a technet article entitled "Chapter 6 - Windows 2000 DNS" - you'll find it on technet by searching on that title. Note that a PTR record is a reverse lookup record. Note the part that clearly states -
"Nslookup can still query the DNS server, and the DNS server can still answer queries"
-----------------------------------------------
Nslookup might also return one of several errors. The following message means that the resolver did not locate a PTR resource record (containing the host name) for the server IP address. Nslookup can still query the DNS server, and the DNS server can still answer queries. For more information about using Nslookup to verify your DNS configuration, see ?Verifying Your Basic DNS Configuration? later in this chapter.
DNS request timed out.
Timeout was <x> seconds.
*** Can't find server name for address <IP Address>: Timed out
*** Default servers are not available
Default Server: Unknown
Address: <IP address of DNS server>

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DNS Problems nslookup failing

by Shanghai Sam In reply to DNS Problems nslookup fai ...

BeerMonster, Great Information! I did solve the problem. What I did was configure three new reverse lookup zones. The initial one I have is: 10.0.0, in it we had all pointers to all machines on our LAN we have three differnt ranges all with the sameSUBNETMASK 10.0.1.x and 10.0.2.x and 10.0.3.x. I created three new reverse lookup zones as follows: 10.0.1 and 10.0.2 and 10.0.3 this coveres all the IPs I have running here on-site. The Asspen(I like this spelling) guys told me that this should notmake a difference; however, I too referred to the documentation and found Chapter 8 in Osborne's Windows 2000 DNS server book to be very, very helpful. Once I created the new reverse lookup zones now get a positive reply when using "nslookup" and our RPC errors between the ASSpen Clients and the ASSpen server are now gone and the ASSpen software is working.
Thank you for your help,
Scott

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DNS Problems nslookup failing

by scottf In reply to DNS Problems nslookup fai ...

This question was closed by the author

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