Declaring subclasses on a per-subnet basis

[Glenn Satchell]

Hi Tihomir

If the option is only required for specific subnets, then perhaps the
group{} functionality would work better, for example:

group {
    option root-path "nfs:192.168.1.1:/nbi:NetInstall-Restore.dmg";

    subnet 10.10.0.0 netmask 255.255.0.0 {
    ...
    }
    subnet 10.11.0.0 netmask 255.255.0.0 {
    ...
    }
}
Or if it is only to be valid in a single subnet you could set the option
in that subnet or pool only.

Classes are more useful for globally matching a subset of hosts based on
some other parameter other than subnet.

regards,
-glenn

On Thu, August 9, 2012 12:36 pm, Hristov, Tihomir H. wrote:
>
>   Dear all,
>
>  I an a Network engineer for Old Dominion University, Norfolk, Virginia
> and my team is looking into a future PXE configuration. We are trying to
> define classes with special options and have them applicable only to some
> special "lab" subnets of the environment.
>
>  Based on research done so far, we have seen that classes and subclasses
> are parsed on a global level and thus would apply to all clients, and
> just the special "lab" subnets.
>
>  Still in a post from June 2012
> (https://lists.isc.org/pipermail/dhcp-users/2012-June/015558.html) we see
> an interesting configuration. Using it as an example, the configuration
> we have in mind would match on a substring of vendor-class-identifier
> (value AAPLBSDPC in this case) and set the root-path option (an example).
> It would look like this:
>
> class "vendor-class" {
> 		match substring(option vendor-class-identifier,0,9);
> }
>
> subnet 10.10.0.0 netmask 255.255.0.0 {
>
>   subclass "vendor-class" "AAPLBSDPC"  {
>      option root-path "nfs:192.168.1.1:/nbi:NetInstall-Restore.dmg";
>   }
>   pool {
> 		option routers 10.10.1.1;
> 		option domain-name-servers 10.101.21;
> 		range 10.10.7.1 10.10.7.254;
> 		option domain-name-servers 10.101.21;
>   }
> }
>
>  The main question here is:
>   1. Would this configuration work as we would like and the class
> declaration would affect only clients in the 10.10.0.0 subnet?
>   2. Or would the ISC DHCP parser end up treating the subclass as a global
> declaration and thus set option root-path to
> "nfs:192.168.1.1:/nbi:NetInstall-Restore.dmg" for all clients,
> regardless of their subnet?
>
>
> In case this would end up a global configuration, we were thinking of
> declaring a class that matches on 2 conditions.
>
>  1. vendor-class-identifier substring
>  2. giaddress
>
>  Since we use DHCP Relay Agents all over our network, we would be able to
> use the giaddress and match it to the special "lab" subnets. We have seen
> some references to
>
>    match if (option dhcp-giaddress-field= 10.10.10.1)
>
>  and we were wondering if that would work. If not, what is the way to
> check the Relay Agent IP Address?
>
>
>  Your help and guidance would be greatly appreciated.
>
>  Sincerely,
>
>  Tihomir Hristov
>  Senior Network Engineer
>  Old Dominion University
>  Office of Computing and Communications Services
>
> _______________________________________________
> dhcp-users mailing list
> dhcp-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users
>