topic Re: DNS issue in Operating System - Linux

DNS issue

WW288996 — Tue, 29 Dec 2009 07:27:53 GMT

I have configured a new DNS server and found that it is working, but the issue is it is taking 10 to 15 seconds when I do ping or ssh with bost name.

For example:

[root@blrdns ~]# ping blrdns
PING blrdns.oesblr.nsn-rdnet.net (10.58.131.246) 56(84) bytes of data.

64 bytes from 10.58.131.246: icmp_seq=25 ttl=64 time=0.009 ms
64 bytes from 10.58.131.246: icmp_seq=26 ttl=64 time=0.009 ms
64 bytes from 10.58.131.246: icmp_seq=27 ttl=64 time=0.009 ms
64 bytes from 10.58.131.246: icmp_seq=28 ttl=64 time=0.009 ms

the ping response (64 bytes from ...)will be coming only after 10 seconds.

But if I do nslookup or host command it is immediatly giving the output.

[root@blrdns ~]# nslookup blrdns
Server: 10.58.131.246
Address: 10.58.131.246#53

Name: blrdns.oesblr.nsn-rdnet.net
Address: 10.58.131.246

[root@blrdns ~]# host blrdns
blrdns.oesblr.nsn-rdnet.net has address 10.58.131.246

Can anyone help me why this is happening.

Re: DNS issue

Matti_Kurkela — Tue, 29 Dec 2009 08:07:43 GMT

What happens if you do:

nslookup 10.58.131.246

or

host 10.58.131.246

If these have a delay, then your problem is with reverse DNS requests.

Are you using BIND or some other DNS server software?

With BIND, you can enable query logging on the DNS server side to see exactly what is happening there. Other DNS server software may allow something similar.

MK

Re: DNS issue

Steven Schweda — Tue, 29 Dec 2009 08:08:08 GMT

> I have configured a new DNS server and
> found that it is working, [...]

Not exactly a complete description of how you
configured this new DNS server, nor of how
you tested it.

> [root@blrdns ~]# nslookup blrdns
> [...]

How well does it work in reverse?:

nslookup 10.58.131.246

Re: DNS issue

WW288996 — Tue, 29 Dec 2009 10:24:30 GMT

I have used bind.
[root@blrdns ~]# rpm -qa | grep bind
ypbind-1.19-9.el5
bind-utils-9.3.4-9.P1.el5
bind-9.3.4-9.P1.el5
bind-libs-9.3.4-9.P1.el5

If I use nslookup/host command then output is coming very fast (with in a second)

If I do nslookup 10.58.131.246 then I am getting the following very fast.

[root@blrdns named]# nslookup 10.58.131.246
Server: 10.58.131.246
Address: 10.58.131.246#53

246.131.58.10.in-addr.arpa name = blrdns.oesblr.nsn-rdnet.net.

But Its not showing hostname while pinging, please find the below ,

[root@blrdns named]# ping 10.58.131.246
PING 10.58.131.246 (10.58.131.246) 56(84) bytes of data.
64 bytes from 10.58.131.246: icmp_seq=1 ttl=64 time=0.027 ms
64 bytes from 10.58.131.246: icmp_seq=2 ttl=64 time=0.009 ms

Re: DNS issue

WW288996 — Tue, 29 Dec 2009 10:29:18 GMT

Please find my config files also below,

[root@blrdns named]# cat /etc/named.conf
options {
directory "/var/named";
};
zone "oesblr.nsn-rdnet.net" {
type master;
file "oesblr.nsn-rdnet.zone";
};
zone "131.58.10.in-addr.arpa" {
type master;
notify no;
allow-query { any; };
file "131.58.10.db";
};

-------------------------------------------

[root@blrdns named]# cat /var/named/oesblr.nsn-rdnet.zone
$TTL 86400
@ IN SOA oesblr.nsn-rdnet.net. root. (
535 ; serial (d. adams)
3H ; refresh
15M ; retry
1W ; expiry
1D ) ; minimum
@ IN NS oesblr.nsn-rdnet.net.
blrdns IN A 10.58.131.246
vm131x185 IN A 10.58.131.185

--------------------------------------------

[root@blrdns named]# cat 131.58.10.db
$TTL 86400
131.58.10.in-addr.arpa. IN SOA blrdns.oesblr.nsn-rdnet.net. root. (
42 ; serial (d. adams)
3H ; refresh
15M ; retry
1W ; expiry
1D ) ; minimum
NS oesblr.nsn-rdnet.net
246 IN PTR blrdns.oesblr.nsn-rdnet.net.
185 IN PTR vm131x185.oesblr.nsn-rdnet.net.

Re: DNS issue

Vitaly Karasik_1 — Tue, 29 Dec 2009 12:16:24 GMT

IMO, this is not reverse DNS problem.
What is your /etc/nsswitch.conf file says about "host"?

Re: DNS issue

WW288996 — Tue, 29 Dec 2009 14:41:56 GMT

nsswitch.conf file has dns as first entry.

hosts dns files

Re: DNS issue

Vitaly Karasik_1 — Tue, 29 Dec 2009 15:17:00 GMT

>the ping response (64 bytes from ...)will >be coming only after 10 seconds.

and ping by IP has no delay?

Re: DNS issue

WW288996 — Wed, 30 Dec 2009 04:15:44 GMT

No ping with IP has no delay.

But it is not showing hostname while pingigng with IP.

Re: DNS issue

Vitaly Karasik_1 — Wed, 30 Dec 2009 07:26:35 GMT

>No ping with IP has no delay.
weird.
what is your resolv.conf? do you have just one DNS server into it ?

>But it is not showing hostname while >pingigng with IP.
it's OK - normal ping behaviour

Re: DNS issue

Vitaly Karasik_1 — Wed, 30 Dec 2009 08:50:46 GMT

another thing - please stop "nscd" (name service cache daemon ) - in many cases it causes problems.

Re: DNS issue

Vitaly Karasik_1 — Wed, 30 Dec 2009 09:51:22 GMT

the same recommendation for "avahi" daemon - disable it.

Re: DNS issue

WW288996 — Thu, 31 Dec 2009 04:11:21 GMT

Hello Vitaly Karasik,

Thanks for your support, It worked halfway.

After stopping of avahi-daemon it is pinging immediatly for the same network but it takes 10 seconds time to ping to other networks.

For exmple,

My name server IP is 10.58.131.246

If I ping some machine in the same network it pings very fast but If I ping some other VLAN for example 10.58.121.xxx then it takes same old 10 seconds time to ping.

I have checked the route, it is alredy there.

Can ypou please help.

Also the reverse lookup is also not working.

Re: DNS issue

Vitaly Karasik_1 — Thu, 31 Dec 2009 10:14:48 GMT

>If I ping some machine in the same network >it pings very fast but If I ping some other >VLAN for example 10.58.121.xxx then it >takes same old 10 seconds time to ping

weird! did you try to ping by IP and it worked fast?

and regarding reverse lookup - do you see any errors from named into syslog?

Re: DNS issue

WW288996 — Thu, 31 Dec 2009 10:17:42 GMT

Hi ,

There was a problem in reverse lookup.

I have corrected it , It is working fine now.

But what is this avahi-daemon is it required for machine.

Thank you very much for the support on time.

Re: DNS issue

Vitaly Karasik_1 — Thu, 31 Dec 2009 14:04:03 GMT

>here was a problem in reverse lookup.
>I have corrected it , It is working fine >now.
do you mean that it's fixed lookup problem, not ping?

>But what is this avahi-daemon is it >required for machine.

As far as I understand - avahi is useless in static server environment, it should help for client configurations. I haven't investigated this issue in-depth - probably tweaking avahi configuration will help...

you're welcome!