NSLOOKUP FAILURE

[Smirjit Singh]

Hi ,

I have configured DNS client my HP D380 Server. It was working perfectly. But sometimes it did not response. When I try to give nslookup command then I get below response.
*** Can't find server name for address < Primary DNS IP>: Timed out
*** Can't find server name for address < BDC IP>: No response from server
*** Default servers are not available
Using /etc/hosts on: hp380d

looking up FILES
Trying DNS
*** can't find www.yahoo.com: No response from server

But if I make reboot then it works fine. I was pinged my PDC & BDC. Everything seems fine. But I did not understand why it is happening.

My Resolv.conf looks like
domain XyZ.co.in
nameserver < PDC IP>
nameserver < BDC IP >

Nsswitch.conf
hosts: files[NOTFOUND=continue UNAVAIL=continue] dns [NOTFOUND=continue UNAVAIL=return]

Would u pls advise me what I should check ?

[Joe Lu_3]

You can try to add PTR entry of your name server to DNS record.

[Printaporn_1]

when the time you get the message name server time out , can you ping the name server IP ?

if sometime it working fine , it couldn't be configuration problem , could be physical network problem.

that you client cannot contact DNS server.

[Smirjit Singh]

Hi,

Our primary name server (NT) is in 203 segment & my HP server is in 208 segment. Everything seems fine. It is also pinging fine. It was working. But somehow it stoppd. If I again reboot now I am sure it would work. Becs I tried earlier then it worked. But I could not understand why it is happening ?

[Steven Sim Kok Leong]

Hi,

When it happens again, try the following:

# telnet IP_of_PDC 53
# telnet IP_of_BDC 53

port 53 is the domain service.

It is most unlikely that both your PDC and BDC domain services would either stop functioning at the same time or get overloaded at the same time.

If the replies to your ICMP request packets (ping) at the time of nslookup failure are fine (ie. no packet losses), then it could possibly meant that there is filtering of domain packets triggered somewhere along the route eg. at firewalls.

Where possible, also perform a tcpdump (can always download) or nettl (never liked it though) on your client interface to very whether domain replies are received when the domain requests are sent.

Hope this helps. Regards.

Steven Sim Kok Leong
Brainbench MVP for Unix Admin
http://www.brainbench.com

[Smirjit Singh]

Hi,

Yes , telnet < PDC IP > 53 is connecting. Ping is also working fine. No data packet loss. I have tested linkloop command & got the below output.
Link connectivity to LAN station: 0x00108336B29F
error: get_msg2 getmsg failed, errno = 4
-- FAILED
frames sent : 1
frames received correctly : 0
reads that timed out : 1

I think it is main culprit. But I could not understand if connection is problem then how it is being able to make ping in same segment or PDC. I don't have very clear idea about linkloop.

[Steven Sim Kok Leong]

Hi,

You should not rely on linkloop. This is because linkloop works only with MAC addresses which are within the same subnetwork. Any MAC addresses beyond your subnetwork is translated automatically by your router.

Given that ping (layer 3) works, layer 2 connectivity should be fine between your client and the router as well as between the router and the PDC.

Try sniffing the client network interface (via tcpdump) using to ascertain that DNS replies are reaching your client. If they are reaching your client machine, then the fault likely lies with your client machine itself. A safe measure would be to install the latest patches related to nslookup.

Also check that you are not running out of connections on your client machine. Check tcp_conn_request_max ndd parameter. Look at your netstat table to see if you are running out of connections. Also perform netstat -i to check your TCP traffic (any losses or discards?), apart from running lanadmin to check your network interface.

Hope this helps. Regards.

Steven Sim Kok Leong
Brainbench MVP for Unix Admin
http://www.brainbench.com

[Plamen SIMEONOV]

Hi,

Some idea:
Would you configure for this HP machine DNS-server. That way we will check if the DNS-client has problems or DNS servers are bad.
Of course in /etc/resolv.conf must make some changes (if you like the idea)
domain domain.com
namaserver 127.0.0.1
nameserver IP_of_PDC
nameserver IP_of_BDC

Plamen

[Steven Sim Kok Leong]

Hi,

One other point.

Note that querying of domain names such as www.yahoo.com require higher level domain servers. If any of the required ones are down, then it is possible that you will not get the IP adress you want.

When your problem happens again, try nslookup an internal domain name (within your own domain) instead of an external one such as www.yahoo.com.

Hope this helps. Regards.

Steven Sim Kok Leong
Brainbench MVP for Unix Admin
http://www.brainbench.com

[Smirjit Singh]

Hi Steven,

I was earler stated that our PDC & BDC is WIN NT server. I did not get any tcpdump software which supports WIN NT. So I could not check it. I think problem is my HP end. Becs when I making nslookup from our NT or WIN2000 workstation then it is working fine. But only HP could not able to fetch the data from NT PDC/BDC.

I tried to configure my HP as DNS server. But also it did not work

[Steven Sim Kok Leong]

Hi,

I had meant tcpdump'ing at your DNS client ie. HP-UX server side to verify that replies have been received. As already mentioned, install all the domain-lookup related patches and make sure that there is no filtering/dropping of domain packets between your DNS client and your PDC/BDC.

Btw, fyi the equivalent of tcpdump on MS Windows is windump which can be downloaded.

Hope this helps. Regards.

Steven Sim Kok Leong
Brainbench MVP for Unix Admin
http://www.brainbench.com