Dual DNS server farms in dhcpd.conf

David Forrest drf at maplepark.com
Tue Apr 28 19:35:39 UTC 2009


I had a lot of DHCPINFO from Vista machines and read somewhere it was due 
to the need of a SRV RR.  I put the following suggested RR in my named 
internal view zone and they stopped.  Don't understand it -- it just 
worked. Post hoc ergo propter hoc?  YMMV.

_ldap._tcp.dc._msdcs	SRV	0 0 0 .

Dave

David Forrest                   e-mail   drf @ maplepark.com
Maple Park Development Corporation  http://xen.maplepark.com
St. Louis, Missouri

On Tue, 28 Apr 2009, Randall C Grimshaw wrote:

> You are correct, but I think Vista has a habit of using info in some cases.
>
> Randy
>
> -----Original Message-----
> From: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of John Tabasz (jtabasz)
> Sent: Tuesday, April 28, 2009 2:05 PM
> To: Users of ISC DHCP; Glenn Satchell
> Subject: RE: Dual DNS server farms in dhcpd.conf
>
>
>
> Randy,
>
> Thanks for the response.
>
> In which cases will dhcpd provide the global, and I'm assuming by global
> we are talking about the non PC specific dns entries, dns addresses?
> What I'm assuming that you are saying is that the dhcpd will respond
> with the "class MSFT" defined dns server addresses when responding to a
> DHCPREQ and the client will come up with the correct dns entries. The
> problem comes in when a DHCPINFO is sent to the dhcpd, in which case the
> global dns entries are sometimes sent in response. Is this true?
>
> DHCPINFO is not something that will happen unless specifically initiated
> by the client. Under what circumstances will a DHCPINFO take place on a
> MSFT client?
>
> Just trying to understand,
>
> John
>
>
>
> -----Original Message-----
> From: dhcp-users-bounces at lists.isc.org
> [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Randall C
> Grimshaw
> Sent: Tuesday, April 28, 2009 10:32 AM
> To: Users of ISC DHCP; Glenn Satchell
> Subject: RE: Dual DNS server farms in dhcpd.conf
>
> This sounds like it should work fairly well for you, but one thing to
> follow-up on is the client behavior when issuing DHCPINFO requests.
> DHCPd will provide the global default DNS in such cases.
>
> We do something like this using the group method as someone else
> suggested to you, but the success is limited to a use case where it is
> non-critical that the users get the correct address every time.
>
> Randy
>
> -----Original Message-----
> From: dhcp-users-bounces at lists.isc.org
> [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of John Tabasz
> (jtabasz)
> Sent: Tuesday, April 28, 2009 1:12 PM
> To: Glenn Satchell; Users of ISC DHCP
> Subject: RE: Dual DNS server farms in dhcpd.conf
>
> Hi Glenn,
>
> This is almost exactly what I was looking for. Thanks for the reply.
> I'll test it out today.
> By the way, how would I have found this information on my own?
>
> Thanks,
>
> John
>
> -----Original Message-----
> From: dhcp-users-bounces at lists.isc.org
> [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Glenn Satchell
> Sent: Monday, April 27, 2009 9:21 PM
> To: dhcp-users at lists.isc.org
> Subject: Re: Dual DNS server farms in dhcpd.conf
>
>
>> Date: Mon, 27 Apr 2009 15:23:09 -0700
>> From: "John Tabasz (jtabasz)" <jtabasz at cisco.com>
>>
>> Hi All,
>>
>> I have a situation where I want to use dhcpd.conf to serve up addresses
>
>> that are statically assigned. I have previously used the following to
>> do
>> this:
>>
>> shared-network TEST  {
>>
>> subnet 192.168.200.0 netmask 255.255.255.0 { option routers
>> 192.168.200.1;
>>  option subnet-mask 255.255.255.0;
>>  option domain-name-servers 10.1.1.25,10.1.2.25,10.1.3.25;
>>  option domain-name "mydomain.com";
>> deny unknown-clients;
>> }
>>
>>  host dev5c.mydomain.com                           {
>>   hardware ethernet              0:3:ba:11:b1:75;
>>   fixed-address                   192.168.200.165;
>>   option host-name                       "dev5c";
>>  }
>>
>> }
>>
>> This worked fine until a new requirement came up that the PCs on the
>> network and the Unix workstations on the same subnet should receive a
>> different set of DNS server IP addresses.
>>
>> I wrote a couple of perl scripts that take the host info and massage it
>
>> into the dhcpd.conf file. One way of getting what I want is to add
>> logic into the scripts that examine the hostname and if the name
>> indicates that the device is a PC, add the correct DNS server info into
>
>> the host declaration. This rather than using the shared-network global
>> command to set the DNS servers for the whole subnet.
>>
>> Is there a DHCP option that returns the kernel that the client is
>> running? If so, is there a way to use this info to manipulate the DNS
>> entries?
>>
>> Suggestions?
>>
>
> This will identify the Windows PCs and override their dns servers. The
> subnet definition stays pretty much as it is, although you don't really
> need the shared-network around the subnet and host definitions.
>
> class "MSFT" {
>  match if substring(option vendor-class-identifier, 0, 4) = "MSFT";
>  option domain-name-servers 10.1.1.26,10.1.2.26,10.1.3.26; }
>
> regards,
> -glenn
>
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-- 
David Forrest                     e-mail   drf at maplepark.com
Maple Park Development Corporation  http://xen.maplepark.com
St. Louis, Missouri



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