[Kea-users] Multi-Class Evaluation in Subnets and Pools (ISC to Kea Migration Pattern)

[Kraishak Mahtha]

Hi All,

In the recent Kea 3.0.4 updates, I noticed that the client-classes
attribute in the subnet/pool configuration is now defined as an array,
which is a good improvement. However, I noticed that we still cannot
directly specify multiple client classes as a comma-separated list and have
them evaluated as a combination.

For example, in the Kea Reference Guide under *16.12.7 – Load Balancing
With Advanced Classification*, multiple classes are created to represent
combinations such as:

=====Sample config=======
{
  "Dhcp4": {
    "client-classes": [{
        "name": "phones",
        "test": "substring(option[60].hex,0,6) == 'Aastra'"
    }, {
        "name": "laptops",
        "test": "not member('phones')"
    }, {
        "name": "phones_server1",
        "test": "member('phones') and member('HA_server1')"
    }, {
        "name": "phones_server2",
        "test": "member('phones') and member('HA_server2')"
    }, {
        "name": "laptops_server1",
        "test": "member('laptops') and member('HA_server1')"
    }, {
        "name": "laptops_server2",
        "test": "member('laptops') and member('HA_server2')"
    }],

     "subnet4": [{
        "id": 1,
        "subnet": "192.0.3.0/24",
        "pools": [{
            "pool": "192.0.3.100 - 192.0.3.125",
            "client-classes": [ "phones_server1" ]
        }, {
            "pool": "192.0.3.126 - 192.0.3.150",
            "client-classes": [ "laptops_server1" ]
        }],

        "option-data": [{
            "name": "routers",
            "data": "192.0.3.1"
        }],
    }]
  }
}
=========================================

This approach works, but it can result in a large number of additional
client classes when we have multiple base classes and need different
combinations for different subnets/pools.

For example, if we have six classes and need:

   -

   Subnet 1 → Class 1 + Class 2 + Class 3
   -

   Subnet 2 → Class 2 + Class 4 + Class 6
   -

   Subnet 3 → Class 1 + Class 5 + Class 6

We would need to create separate combination classes for each required
combination. This can make the configuration large and difficult to
maintain.

In ISC DHCP, this can be handled more easily using statements such as:

allow members of "class1";
allow members of "class2";

and additional classes can be added independently as required.

Can anyone please suggest whether there is an existing Kea mechanism or a
recommended approach to handle such class combinations without creating a
separate class for each combination?

If not, this is a useful enhancement/feature request for Kea, allowing
multiple client classes to be associated with a pool and evaluated
independently, similar to the allow members of approach in ISC DHCP.

Thanks in Advance
Kriashak
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