Question

NSSWITCH.CONF file and DNS issue

Asked by: rbkumaran

I'm testing my nsswitch.conf file owing to some resolving issues on my sun solaris (8) boxes.

My nsswitch.conf file has the config for hosts as

hosts: dns [NOTFOUND=return] files nis

I'm sure this means when DNS server is available and that it says there isn't a record that exist for this query then return the same back to the client and not to check the "files".

However, when I check adding a dummy host entry in /etc/hosts file and then trying to ping the host, I can still ping the device even though the nsswitch.conf shouldnt allow it.

I did restart the nscd daemon to clear the cache but that doesn't help.

Any ideas???

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Asked On
2007-07-10 at 06:05:22ID22685740
Tags

solaris

,

dns

Topic

Sun Solaris

Participating Experts
3
Points
125
Comments
15

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Answers

 

by: CaseybeaPosted on 2007-07-10 at 07:03:00ID: 19453633

try:

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

 

by: rbkumaranPosted on 2007-07-10 at 07:10:27ID: 19453723

I did try and it doesn't help. Moreover, this means that the DNS server should be checked for a record also in case of DNS server being unavailable return the results back to the client but my requirement is to stop from going beyond the DNS server (to test). Every other combination seems OK. For example, set "hosts: nis [NOTFOUND=return] files dns" where it returns straight after the NIS check.

 

by: CaseybeaPosted on 2007-07-10 at 08:00:34ID: 19454303

What does your /etc/resolv.conf look like?  

 

by: rbkumaranPosted on 2007-07-10 at 08:03:38ID: 19454331

right dns servers in correct domain search order

nameserver x.x.x.x
nameserver y.y.y.y
search xyz.com

 

by: CaseybeaPosted on 2007-07-10 at 13:37:12ID: 19457511

I wonder if the dns [notfound....] behavior only works when the LOCAL host is also a dns server?

Just a thought; this is after all solaris :-(

 

by: TintinPosted on 2007-07-10 at 15:40:53ID: 19458446

I think the issue here is not so much the nsswitch.conf configuration, but what tools actually consult it.

From memory, I think ping may not actually consult nsswitch.conf.

You're better off testing by using something like telnet or ftp to test the dummy address you've added to /etc/hosts

 

by: JustUNIXPosted on 2007-07-11 at 00:29:49ID: 19460399

Verify with
   getent hosts <hostname>
to see what actually gets resolved. This way, it uses nsswitch.conf

 

by: rbkumaranPosted on 2007-07-11 at 01:09:37ID: 19460510

I did a GETENT and have rather interesting results.

1. When I remove FILES from nsswitch.conf file and do a getent for a host listed only on hosts file, it fails.

2. When I remove DNS from nsswitch.conf file and do a getent, I can still get the name resolution happening. (I've restarted nscd to clear cache)



 

by: JustUNIXPosted on 2007-07-11 at 01:11:54ID: 19460524

how does your "hosts" entry look like in nsswitch.conf actually?

# grep '^hosts:' /etc/nsswitch.conf

 

by: TintinPosted on 2007-07-11 at 01:12:32ID: 19460529

What version of Solaris are you running?  nscd has been know to have a lot of issues in older Solaris versions and in fact, a lot of people disable it.

 

by: rbkumaranPosted on 2007-07-11 at 01:13:42ID: 19460535


hosts:      dns [NOTFOUND=return] files nis

 

by: JustUNIXPosted on 2007-07-11 at 01:36:36ID: 19460618

Does a
  # nslookup hostname
return successfully (no such domain) or is DNS not working correctly?

If DNS does not answer "not found" FILES will be tried next. Searching will only stop if DNS replies with a NOT FOUND condition.

You may also want to stop nscd while testing your nsswitch.conf

 

by: rbkumaranPosted on 2007-07-11 at 02:54:31ID: 19460956

Stopped nscd.

NSLOOKUP works OK as it looks at the /etc/resolv.conf directly which has the Windows DNS servers rsponding.

I know NOT FOUND=return will stop looking at the next database only if NOT FOUND answer is returned and that is exactly what I'm trying to prove works right...I've added a host entry in the /etc/hosts for a host not avialable on the DNS servers to test this



 

by: JustUNIXPosted on 2007-07-11 at 03:37:52ID: 19461163

any change if nscd is not running?

 

by: rbkumaranPosted on 2007-07-11 at 03:39:52ID: 19461170

Unfortunately NO.

20120131-EE-VQP-002

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