[Kea-users] IPv4 DDNS with existing IPv6 AAAA records

[Darren Ankney]

Hi,

See: https://kea.readthedocs.io/en/kea-2.4.0/arm/ddns.html#conflict-resolution.
In Kea, you can disable `ddns-use-conflict-resolution` which will
cause ddns to send the update regardless of what is there already.
This should be used with caution.  If there are conflicting hostnames
from disparate clients, then there will be problems.  This setting is
probably best used with settings like:

        "ddns-generated-prefix": "dynamic",
        "ddns-replace-client-name": "always",

so that you can be sure that no user setting on the client itself can
cause problems.  See:
https://kea.readthedocs.io/en/kea-2.4.0/arm/dhcp4-srv.html#kea-dhcp4-name-generation-for-ddns-update-requests
for details.

Thank you,

Darren Ankney

On Mon, Jul 24, 2023 at 9:58 AM Brian J. Murrell <brian at interlinx.bc.ca> wrote:
>
> Beyond being EoL, the (other) ISC DHCP server product
> (https://www.isc.org/dhcp/) has a problem in the use-case where you
> want to have DHCP for your IPv4 addresses and have IPv6 (AAAA)
> addresses for the same hosts in your DNS already.
>
> The problem is because the ISC DHCP server is gating adding the A
> record for the IPv4 DHCP lease on there being *no other* (not just
> other A) records in the zone for the host.
>
> When one adds AAAA records for the same host that ISC DHCP wants to
> dynamically add A records for you get the following errors:
>
> Jul 24 09:17:22 server named-pkcs11[3550049]: client @0x7f6c27bb3b30 10.75.22.247#47279/key linux_home_nsupdate: updating zone 'example.com/IN': update unsuccessful: brian-laptop.example.com: 'name not in use' prerequisite not satisfied (YXDOMAIN)
> Jul 24 09:17:22 server named-pkcs11[3550049]: client @0x7f6c24ed2c40 10.75.22.247#48765/key linux_home_nsupdate: updating zone 'example.com/IN': update unsuccessful: brian-laptop.example.com/TXT: 'RRset exists (value dependent)' prerequisite not satisfied (NXRRSET)
> Jul 24 09:17:22 server dhcpd[5836]: Forward map from brian-laptop.example.com to 10.75.22.217 FAILED: Has an address record but no DHCID, not mine.
>
> This makes using the ISC DHCP server in a dual-stack environment
> horrible.
>
> Does the Kea DHCP server have the same problems or can it successfully
> dynamically update the A record even when there are other pre-existing
> records, such as AAAA, for the same host?
>
> Cheers,
> b.
>
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