topic Re: Question about hostname resolve in Operating System - HP-UX

Question about hostname resolve

chuanpeng.wang — Thu, 31 Jul 2008 08:51:39 GMT

Is there system process will resolve the other server's IP to the hostname?
I found DNS packet in TCP packets, but I don't know which process do this.
I don't have DNS on my server.

/etc/nsswitch.conf
hosts: files[NOTFOUND=continue] dns

Re: Question about hostname resolve

H_16 — Thu, 31 Jul 2008 08:53:45 GMT

Use your host file in /etc/

Re: Question about hostname resolve

Sharma Sanjeev — Thu, 31 Jul 2008 09:28:39 GMT

Hi

Add entry in /etc/hosts file

with Hostname and ip address

Regards
Sanjeev

Re: Question about hostname resolve

Torsten. — Thu, 31 Jul 2008 09:33:24 GMT

>> "I don't have DNS on my server.

/etc/nsswitch.conf
hosts: files[NOTFOUND=continue] dns "

But this line looks like you have (continue to DNS)!

Do you have a config in

/etc/resolv.conf ?

Re: Question about hostname resolve

Torsten. — Thu, 31 Jul 2008 09:36:58 GMT

Easy test:

# nslookup www.hp.com

Re: Question about hostname resolve

Masud Parvez — Thu, 31 Jul 2008 09:37:38 GMT

you can add your hostname and IP address to the /etc/hosts file

or you can point to your existing DNS server by giving entry into /etc/resolv.conf

example (IP=DNS server IP address)
nameserver IP

Re: Question about hostname resolve

Torsten. — Thu, 31 Jul 2008 09:45:46 GMT

I don't think the question is "how to resolve", but "why it is asking DNS".

IMHO the answer is in /etc/nsswitch.conf.

A process wants to resolve a hostname that is not in the hosts file.

That's why I wrote about the easy test - you will just see what happens.

# nslookup www.hp.com
Using /etc/hosts on: xyz

looking up FILES
==> Trying DNS <==
...
Aliases: www.hp.com

Re: Question about hostname resolve

Steven E. Protter — Thu, 31 Jul 2008 09:51:19 GMT

Shalom,

If you have no DNS server to work with then nsswitch.conf should not have a configuration that tries to continue to a non-existent DNS server. That will simply slow network operations on your system. Better to simply let /etc/hosts resolve or fail and get an answer back quickly.

SEP

Re: Question about hostname resolve

Deepak Kr — Thu, 31 Jul 2008 09:57:56 GMT

Hi chuanpeng.wang

If other node information is not found in your local /etc/hosts then only resolution process will move to dns as next resort.

So you have two choices as everyone told.
either use /etc/hosts
or
use DNS server to resolve hostname/IP

File: /etc/hosts
File: /etc/resolv.conf

Re: Question about hostname resolve

chuanpeng.wang — Fri, 01 Aug 2008 00:44:43 GMT

Sorry, I mislead you.
My question is which process ask for DNS resloving.

In the TCP packet, I found some process try to resolve the IP to hostname, but I don't know which process do this.
It seems some system process, because my user application will not do this.
Which system process will try to resolve IP to hostname?
Please give me some example.

Re: Question about hostname resolve

Deepak Kr — Fri, 01 Aug 2008 00:47:29 GMT

If I am not wrong it is inetd service.

Re: Question about hostname resolve

Patrick Wallek — Fri, 01 Aug 2008 01:01:44 GMT

There is no 'system process' that does DNS resolution. This is done by via system calls to networking type routines.

If you can resolve host names to IP addresses, via tools like nslookup, dig, ping, etc., but your application can not, then you application is designed badly and is not really network aware.

I would talk to the application vendor if this is a purchased app. If this is an in-house developed app, then the developers need to go back a look at their code.

Re: Question about hostname resolve

Patrick Wallek — Fri, 01 Aug 2008 01:03:24 GMT

By the way, DNS resolution has absolutely nothing to do with inetd.

Processes started by inetd (telnet, ftp, remsh, rcp, etc.) are network aware and have code built in (or probably more accurately call libraries) that does the network name / IP address lookup.