Selecting fixed or dynamic address based on vendor-class-identifier

[Glenn Satchell]

Hi Anders

Without the host statement, ie assuming you were using a dynamic address
in both subnets this would be easy. Allow pxeclient class in one pool and
deny it in the other.

class "pxeclient" {
    match if substring (option vendor-class-identifier, 0, 9) = "PXEClient";
}

shared-network all {
    subnet 192.168.254.0 netmask 255.255.255.0 {
    pool {
      allow members of "pxeclient";
      range 192.168.254.100 192.168.254.109;
    }
  }

    subnet 192.168.255.0 netmask 255.255.255.0 {
    pool {
      deny members of "pxeclient";
      range 192.168.255.100 192.168.255.109;
    }
  }
}

With the host statement, anything in there applies whether we are
pxe-booting or normal booting, so need to be careful how we do things.
That's why you can't put ignore-booting in the host statement as it will
apply in both cases. I'm not entirely sure this will work, but it might
give you an idea.

host boottest {
    hardware ethernet 02:13:10:07:11:58;
    if substring (option vendor-class-identifier, 0, 9) != "PXEClient" {
        fixed-address 192.168.255.12;
    }
}

fixed-address has higher preference than dynamic address.

Not sure if you can do this, it's only a siggestion, but maybe just let
clients pxe-boot using their fixed ip-address? Add the details for boot
server and filename to the pxeclient class. It would make the dhcpd.conf
much simpler.

regards,
-glenn

On Tue, October 22, 2013 2:24 am, Sten Carlsen wrote:
> My take on this would be to test this:
>
> class "pxeclient" {
>     match if substring (option vendor-class-identifier, 0, 9) =
> "PXEClient";
>   }
>
>   host boottest {
>     hardware ethernet 02:13:10:07:11:58;
>     fixed-address 192.168.255.12;
>   }
>
>
> shared-network all{
>     subnet 192.168.254.0 netmask 255.255.255.0 {
>     pool {
>       allow members of "pxeclient";
>       range 192.168.254.100 192.168.254.109;
>     }
>   }
>
>     subnet 192.168.255.0 netmask 255.255.255.0 {
>       deny members of "pxeclient";   }
> }
>
> The uncertain point here is that in a shared network there is really
> nothing to tell which subnet the host belongs to, no DHCP-Relays etc.
> This should work if a class has higher preference than a host statement.
>
> I don't know the answer to that, I would have to test it.
>
> On 21/10/13 17.06, Anders Blomdell wrote:
>> I would like the ISC dhcpd server to hand out either a dynamic ip
>> address or
>> a fixed address based on the vendor-class-identifier (I want a dynamic
>> address
>> from one subnet during pxeboots and a [possibly] fixed address from
>> another
>> subnet otherwise). I have been able to do it by running two instances
>> of the
>> dhcp server on the interface, but not by using shared-network.
>>
>> The working configuration consists of /tmp/254.conf:
>>
>>   class "pxeclient" {
>>     match if substring (option vendor-class-identifier, 0, 9) =
>> "PXEClient";
>>   }
>>
>>   subnet 192.168.254.0 netmask 255.255.255.0 {
>>     pool {
>>       allow members of "pxeclient";
>>       range 192.168.254.100 192.168.254.109;
>>     }
>>   }
>>
>> and /tmp/255.conf:
>>
>>   host boottest {
>>     hardware ethernet 02:13:10:07:11:58;
>>     fixed-address 192.168.255.12;
>>     if substring(option vendor-class-identifier, 0, 9) = "PXEClient" {
>>       ignore booting;
>>     }
>>   }
>>   subnet 192.168.255.0 netmask 255.255.255.0 {
>>   }
>>
>> when running both of them with:
>>   /usr/sbin/dhcpd -d -cf /tmp/254.conf -lf /tmp/254.lease --no-pid
>>   /usr/sbin/dhcpd -d -cf /tmp/255.conf -lf /tmp/255.lease --no-pid
>>
>> I get the following expected result:
>>
>>   # PXE-booting
>>   DHCPDISCOVER from 02:13:10:07:11:58 via eth0
>>   DHCPOFFER on 192.168.254.100 to 02:13:10:07:11:58 via eth0
>>   # Ordinary boot
>>   DHCPDISCOVER from 02:13:10:07:11:58 via eth0
>>   DHCPOFFER on 192.168.255.12 to 02:13:10:07:11:58 via eth0
>>
>> But I'm not able to achieve it with just one instance of dhcpd,
>> the reason seems to be that the 'ignore booting' will be active
>> for both subnets when the machine is PXE-booting and hence it will
>> not get an address from the pool.
>>
>> Anybody that has a good idea on how to solve this?
>>
>> Regards
>>
>> Anders
>>
>
> --
> Best regards
>
> Sten Carlsen
>
> No improvements come from shouting:
>
>        "MALE BOVINE MANURE!!!"
>
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