etc/resolv.conf not resolving two Windows Domain Controlers

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sjose
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Joined: 2018/09/07 13:25:23

etc/resolv.conf not resolving two Windows Domain Controlers

Post by sjose » 2018/09/07 13:52:44

Hi,
We have problem to communicate with a number of windows hosts from a CentOS 6.9 host.

The Set is like below,

All nodes are in the same subnet, including the CentOS node,

From the windows side, there is a Management node configured using Active directory, there can be a number of hosts configured under this management node.

In the CentOS box, this Management node ip is configured in the etc/resolv.conf as below

Code: Select all


options timeout:1 attempts:1
nameserver IDM04MG1.IDM04.iyntax.net      # hostname of the MG node
nameserver 192.168.59.132                         #  IP of the MG node


now from the, CentOS box its possible to communicate to all the nodes, those are coming under this particular MG node... No issue here.


But when we have to communicate to more than one set up, where the configuration is similar, its not happening,

That is in the etc/resolv.conf

Code: Select all


options timeout:1 attempts:1
nameserver IDM04MG1.IDM04.iyntax.net        # hostname of the First MG node
nameserver 192.168.59.132                            # IP of the First MG node
nameserver SHDMG1.SHD.iyntax.net        # hostname of the second MG node
nameserver 192.168.59.156                             # IP of the second MG node

With the above configuration, its only possible to establish communication with the First MG (IDM04MG1.IDM04.iyntax.net) node (ping IDM04MG1.IDM04.iyntax.net works) and the nodes coming under that.

But when its comes to the second one (SHDMG1.SHD.iyntax.net), its not at all possible to communicate,

Code: Select all

ping SHDMG1.SHD.iyntax.net  #  Fails


If I change the order as below

Code: Select all


options timeout:1 attempts:1
nameserver SHDMG1.SHD.iyntax.net              # hostname of the First MG node
nameserver 192.168.59.156                           # IP of the First MG node
nameserver IDM04MG1.IDM04.iyntax.net        # hostname of the second MG node
nameserver 192.168.59.132                           # IP of the Second MG node



its only possible to establish communication with the SHDMG1.SHD.iyntax.net node (ping SHDMG1.SHD.iyntax.net works) and the nodes coming under that.

But not with the second one, I'm stuck at the moment with it, Please help me.
Last edited by sjose on 2018/09/10 09:04:27, edited 1 time in total.

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TrevorH
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Re: etc/resolv.conf not resolving two dns

Post by TrevorH » 2018/09/07 14:08:41

First, you can't use names on nameserver lines. Well, apparently can you try but then you would get into a chicken/egg situation in that you need a name server to resolve the name of the nameserver... Running man resolv.conf starts off with
nameserver Name server IP address
Internet address of a name server that the resolver should query, either an IPv4 address (in dot notation), or an
IPv6 address in colon (and possibly dot) notation as per RFC 2373.
Second, you seem to not quite understand how it works on linux (and possibly other o/s's too). Only the first name server is ever used. Only if there is no response from the first one will the next one be consulted. If the first one replies with a "Never heard of it" then that is the final answer and the search stops. If it replies with the correct info then that's the end of the search and no more are used either. You can specify options rotate which causes round-robin selection of nameservers from among those listed (i.e. the 1st query will consult the first nameserver then the next query will use the 2nd etc). But it still won't use more than one for each lookup unless the first server consulted returns no answer within the timeout period.
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sjose
Posts: 4
Joined: 2018/09/07 13:25:23

Re: etc/resolv.conf not resolving two dns

Post by sjose » 2018/09/10 09:02:24

I tried as below,

Code: Select all


options timeout:1 attempts:1 rotate

nameserver 192.168.59.132                           # IP of the First MG node (IDM04MG1.IDM04.iyntax.net)
nameserver 192.168.59.156                           # IP of the Second MG node (SHDMG1.SHD.iyntax.net)

but it did not help...

Its possible to ping seemlessly to both IP, but when it comes to Domain Controllers, hostname its not happening..

Code: Select all


ping 192.168.59.132                                    # Works
ping 192.168.59.156                                    # Works
ping IDM04MG1.IDM04.iyntax.net                  # Works
ping SHDMG1.SHD.iyntax.net                        # Not Working 


See the nslookup command out put.

Code: Select all

nslookup -type=any IDM04MG1.IDM04.iyntax.net

Server:         192.168.59.132
Address:        192.168.59.132#53

Name:   IDM04MG1.IDM04.iyntax.net
Address: 192.168.59.132
IDM04MG1.IDM04.iSyntax.net      has AAAA address fd00:59::250:56ff:febc:75ee

Code: Select all

##################################
nslookup -type=any SHDMG1.SHD.iyntax.net
;; Got recursion not available from 192.168.59.132, trying next server
Server:         192.168.59.156
Address:        192.168.59.156#53

Name:   SHDMG1.SHD.iyntax.net
Address: 192.168.59.156

Is it because of IPV6...?

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TrevorH
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Re: etc/resolv.conf not resolving two Windows Domain Controlers

Post by TrevorH » 2018/09/10 10:20:06

Only the first name server is ever used. Only if there is no response from the first one will the next one be consulted. If the first one replies with a "Never heard of it" then that is the final answer and the search stops
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sjose
Posts: 4
Joined: 2018/09/07 13:25:23

Re: etc/resolv.conf not resolving two Windows Domain Controlers

Post by sjose » 2018/09/11 05:10:06

I very much require the communication to two Windows Domain controllers simulatneously from a CentOS 6.9 Box..

Can I configure dnsmasq here..? will it help ..?

tunk
Posts: 448
Joined: 2017/02/22 15:08:17

Re: etc/resolv.conf not resolving two Windows Domain Controlers

Post by tunk » 2018/09/11 12:18:37

I have no experience with Windows Domain Controllers, but to me this looks like a windows DNS problem.
I would guess that you will have to setup your first DNS to resolve the second and vice versa.
You should also upgrade to 6.10 as there's no (security) updates for 6.9.

sjose
Posts: 4
Joined: 2018/09/07 13:25:23

Re: etc/resolv.conf not resolving two Windows Domain Controlers

Post by sjose » 2018/09/18 06:26:01

It worked with the below configuration

Installed the dnsmasq library in the CentOS box, and configured the server in the /etc/dnsmasq.conf file, with the part of FQDN as below.

server=/IDMT.iSyntax.net/192.168.59.156
server=/IST.iSyntax.net/192.168.59.132

tunk
Posts: 448
Joined: 2017/02/22 15:08:17

Re: etc/resolv.conf not resolving two Windows Domain Controlers

Post by tunk » 2018/09/18 11:51:14

Adding entries in /etc/hosts might also have solved the problem.

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