Configuration by subclass and subnet

Simon Hobson dhcp1 at
Thu Oct 18 06:53:21 UTC 2012

Joao E Pereira Jr wrote:

>My organization has only one DHCP server that provides configuration for
>clients in all subnets and every subnet gateway is able to do dhcp relay. In
>some subnets there are access points that look for a wireless switch
>controller using the value of option 43 of reply packet. Currently it have two
>controllers and I need to include option 43 only for the access points
>assigning the value based on the subnet.
>Subclassing allow me to include option 43 only for the access points, but I
>haven't found a way to assign the value based on subnet so far. I' ve tryed
>conditional behavior as showed in dhcp-eval. All access points end up reaching
>the same controller or got no option 43 at all. Is this scenario feasible?

Does it matter if a few devices get Option43 that aren't access 
points ? If not, then just define the option at the subnet level and 
each device will get the right value automatically. Devices should 
only be sent the option if they ask for it.

Alternatively, how are you addressing the access points - dynamically 
or statically ? And if dynamically, how much spare address space do 
you have ?
One option would be to have a separate pool for the access points, 
and make that available only to them by the same class & subclass you 
have now. Then add the option in the pool scope.

Otherwise, you'll end up with a big if ... elseif ... elseif ... 
statment checking the GI Address field for the subnet and setting the 
option accordingly - messy.
Simon Hobson

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