[Kea-users] assigning pools based on DHCPv4 relay id

[Lexi Winter]

hello,

i'm using Kea to serve a single IPv4 network, which we'll call
192.0.2.64/26.  this network is presented as a single /26 to clients,
but it's routed internally, which means clients on a specific switch
need to be allocated IP addresses from a pool containing the addresses
routed to that switch.  the switches use a standard DHCP relay to
forward requests to Kea.

in diagram form:

                  [Kea] ------- [wireless controller]
                  /    \           192.0.2.88/29,
                 /      \          192.0.2.96/27
                /        \
               /          \
        [switch 1]       [switch 2]
      192.0.2.66/32,   192.0.2.68/32,
      192.0.2.70/32    192.0.2.80/32

so for example, if Kea receives a request from the wireless DHCP relay,
it needs to allocate an address from either the /29 or /27 network
routed to the wireless controller.  in some cases, like the other two
switches, the addresses are not contiguous and might be represented as
a set of /32 prefixes.

i tried to do this with a client class, like this:

  "client-classes": [
    {
      "name": "wireless",
      "test": "relay4[2].hex == 'wireless'"
    }
  ],
  // ...
  "subnet4": [
    {
      "id": 1,
      "subnet": "192.0.2.64/26",
      "pools": [
         {
          "pool": "192.0.2.88 - 192.0.2.126",
          "client-classes": [ "wireless" ]
        }
      ],
    }
  ],

however this doesn't seem to work; Windows in particular is very unhappy
with this configuration and never acquires its initial lease. 

i think what happens is the initial address allocation via the relay
works fine, but when the client sends a unicast request directly to Kea,
it's no longer a member of the "wireless" class and Kea has no pool for
it to use.

is there another way to do this?  i'm considering using a separate
subnet for each pool and overriding the netmask in the response, but
having a separate subnet for every /32 prefix doesn't seem like a
very clean way to do this.

thanks in advance for any advice.
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