[Kea-users] Subnet ID max value?

[Ashwani Kumar]

Hi Jim

You can use any unique numbers for this. I am using like this and working

{
        "id": 32,
        "subnet": "172.16.32.0/24",
        "pools": [
          {
            "pool": "172.16.32.50 - 172.16.32.250"
          }
        ],
        "option-data": [
          {
            "space": "dhcp4",
            "name": "domain-name-servers",
            "code": 6,
            "data": "172.16.11.30, 172.16.11.31"
          },
          {
            "space": "dhcp4",
            "name": "domain-name",
            "code": 15,
            "data": "example.com"
          },
          {
            "space": "dhcp4",
            "name": "routers",
            "code": 3,
            "data": "172.16.32.1"
          },
          {
            "space": "dhcp4",
            "name": "broadcast-address",
            "code": 28,
            "data": "172.16.32.255"
          }
        ],
        "valid-lifetime": 86400,
        "max-valid-lifetime": 864000
      },
      {
        "id": 40,
        "subnet": "172.16.40.0/24",
        "pools": [
          {
            "pool": "172.16.40.50 - 172.16.40.250"
          }
        ],
        "option-data": [
          {
            "space": "dhcp4",
            "name": "domain-name-servers",
            "code": 6,
            "data": "172.16.11.30, 172.16.11.31"
          },
          {
            "space": "dhcp4",
            "name": "domain-name",
            "code": 15,
            "data": "example.com"
          },
          {
            "space": "dhcp4",
            "name": "routers",
            "code": 3,
            "data": "172.16.40.1"
          },
          {
            "space": "dhcp4",
            "name": "broadcast-address",
            "code": 28,
            "data": "172.16.40.255"
          }
        ],
        "valid-lifetime": 86400,
        "max-valid-lifetime": 864000
      },

On Wed, Aug 27, 2025 at 11:25 PM <jim at wrightthisway.com> wrote:

> On 2025-08-27 12:15, Ben Scott wrote:
> > On 8/27/25 12:33, Jim wrote:
> >> My big question is the ID for each subnet,
> >> I see no info in the docs on if there is a max value for this,
> >
> >   At present it is a 32-bit unsigned integer.  So 4294967295 is the
> > largest possible value (2^32-1, since it counts from zero).
> >
> >   It is defined in src/lib/dhcpsrv/subnet_id.h in the code.
> >
> >> my second concern would be if using large(ish)
> >> values would have any performance impact.
> >
> >   I'm not aware of any.  It's supposed to just be an opaque identifier.
> > There are plenty of people using "large" values here without complaint.
>
> Thank you Ben and Jonas!  I did try searching the docs for this but
> searching for 'subnet' and 'id' weren't helpful.  LOL
>
> Jim
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