topic Re: DNS in Operating System - HP-UX

DNS

Tim King_3 — Mon, 19 Sep 2005 10:35:18 GMT

Not sure what's happening but our HPUX 9000 11.0 server may be having a problem resolving host names. The majority of the users on our network run a telnet session to our main app through Accuterm. All of a sudden there is a long delay before you get a login. Anywhere from 30 seconds to 15 min. Also there is some email sent from the server that is not going out. When I telnet to the port 25 and type "mail from: emailaddress" I get: "Sender domain must resolve" I'm not that familiar with hpux, can someone help me troubleshoot this?

Thanks
Tim

Re: DNS

Uday_S_Ankolekar — Mon, 19 Sep 2005 10:40:11 GMT

This could be due to setttings in /etc/resolv.conf file.

It should have entries like this
domain yourdomain.name
name server x.x.x.x (Ip Address of DNS server)
name server x.x.x.x ( Secodary DNS server )

You /etc/nsswtich.conf file should like this for DNS resolution
hosts: files [NOTFOUND=continue UNAVAIL=continue] dns [NOTFOUND=return UNAVAIL=continue TRYAGAIN=return]

-USA..

Re: DNS

Orhan Biyiklioglu — Mon, 19 Sep 2005 10:44:41 GMT

Check the contents of the file /etc/resolv.conf
Are the nameservers specified correctly and use the nslookup command whether you can resolve from the DNS servers specified.

Re: DNS

Hakan Aribas — Mon, 19 Sep 2005 10:49:49 GMT

Please make sure that your DNS server can make reverse DNS queries. In our environment, we had a very similar problem with Weblogic server. After enabling reverse dns and adding prt records of server, there is no problem :-)

Re: DNS

Tim King_3 — Mon, 19 Sep 2005 11:00:31 GMT

How would I check or enable reverse DNS?

Thanks

Re: DNS

Mel Burslan — Mon, 19 Sep 2005 11:01:12 GMT

Tim,

if you are not the administrator of dns servers, check with the people who perform this function to see if they took the dns servers down or changed the ip addresses of DNS Servers without telling people like you. If you are working in a predominantly windows centric environment, Active driectory tied dns, may change transparent to windows users but have dire consequences for other types of servers.

Re: DNS

Mel Burslan — Mon, 19 Sep 2005 11:02:04 GMT

if you can provide this output, it would help tremendously as well:

cat /etc/nsswitch.conf
cat /etc/resolv.conf
cat /etc/hosts

Re: DNS

Tim King_3 — Mon, 19 Sep 2005 11:26:15 GMT

resolv.conf

nameserver 192.99.99.163
#domain jmg
#nameserver 10.220.1.10
#nameserver 10.220.2.10

nsswitch.conf

#hosts: dns [NOTFOUND=continue] files
hosts: files [NOTFOUND=continue] dns

Re: DNS

Mel Burslan — Mon, 19 Sep 2005 11:29:19 GMT

can you ping or telnet/ssh to the dns server at IP address 192.99.99.163 ? You do not need to have a login but do you know it is alive and accesible from your network. SOmetimes, strange subnetting or inserting an additonal router between your server and this one may cause you some headaches

Re: DNS

Tim King_3 — Mon, 19 Sep 2005 11:35:07 GMT

Yes I can, the 2 conf files reside on that server.

Re: DNS

Mel Burslan — Mon, 19 Sep 2005 11:40:54 GMT

before the nameserver line in your /etc/resolv.conf, insert your domain as follows

(if your server's fully qulaified domain name is myserver.lab.mycompany.com")

domain lab.mycompany.com

this may help you get past the sendmail problem.

after doing this, make an nslookup query to another remote server in your company. How long does it take you to get the response back ? almost immediately or is there some sort of a delay ?

Re: DNS

Bill Hassell — Mon, 19 Sep 2005 11:55:05 GMT

Normal DNS queries are hostnames, returning an IP address. Reverse DNS queries are IP addresses returning hostnames. It is a classic DNS config problem when telnet delays for 20-30 seconds per DNS server in /etc/resolv.conf. It means that the incoming computer (PC, server, etc) is unknown to the DNS server and telnet is trying to validate that this client should even be allowed to connect. When reverse DNS fails, the resolver then tries the next DNS server, and then the next. Each one requires about 20-30 seconds to timeout. If you wait for more than 90 seconds, you'll get a normal login. This is a standard security procedure and cannot be turned off.

Start by changing the default /etc/nsswitch.conf so that the resolver will look in /etc/hosts on the server first. Change this line:

hosts: dns [NOTFOUND=return] nis [NOTFOUND=return] files

to

files [NOTFOUND=continue UNAVAIL=continue] dns [NOTFOUND=return UNAVAIL=continue TRYAGAIN=return]

To see if the PC is not in the DNS server, login and type: nslookup 12.34.56.78
where 12.34.56.78 is the IP address of your PC. If you get no hostname in return (ie, can't find ... Non-existent domain) then the problem is with the DNS server--it is not connected to your DHCP server and the assigned IP addresses from DHCP have no hostnames.

To get rid of the delays, fix your DNS server (they probably deleted all the reverse lookup records, thus causing the problem), or get all of the po9ssible DHCP addresses in your company, assign them arbitrary names like dummy1234, dummy1235, etc, and put that list into all your /etc/hosts files (after changing /etc/nsswitch.conf).

Re: DNS

Tim King_3 — Tue, 20 Sep 2005 13:37:54 GMT

It turned out to be a missing entry in the host file for our secondary DNS server. It's strange because I'm sure it was never there to begin with.

I would like to thank you all for the generous responses!!

Tim

Re: DNS

Bill Hassell — Tue, 20 Sep 2005 15:31:17 GMT

Usually this means the DNS servers do not know each other's names--a common error in administering DNS servers. All DNS servers should know about each other and be able to return a name in response to a query about the IP address (reverse lookup).