[Kea-users] Error: Unable to override definition of option '121' in standard option space 'dhcp4'

[Darren Ankney]

Hi Mark,

> Is there a way to get around the error "unable to override definition of option '121' in standard option space 'dhcp4' "?

Yes.  This article describes such a method:
https://kb.isc.org/docs/redefining-standard-options

Thank you,
Darren Ankney

On Sat, May 31, 2025 at 6:33 PM ldm--- via Kea-users
<kea-users at lists.isc.org> wrote:
>
> Hi!
>
> With recent Kea version 2.6.2 I am getting:
> Error encountered: unable to override definition of option '121' in standard option space 'dhcp4'.
>
> Because my kea-dhcp4.conf relies on:
>
> "option-def": [
>   {
>     "space": "dhcp4",
>     "name": "rfc3442-classless-static-routes",
>     "code": 121,
>     "array": true,
>     "type": "record",
>     "record-types": "uint8,uint8,uint8,uint8,uint8,uint8,uint8,uint8"
>   },
>   {
>     "space": "dhcp4",
>     "name": "ms-classless-static-routes",
>     "code": 249,
>     "array": true,
>     "type": "record",
>     "record-types": "uint8,uint8,uint8,uint8,uint8,uint8,uint8,uint8"
>   }
> ]
>
> with some research I found issue #3074
> https://gitlab.isc.org/isc-projects/kea/-/issues/3074
>
>
> and a one year old merge request #2135
> https://gitlab.isc.org/isc-projects/kea/-/merge_requests/2135
>
> The issue states:
>
> > While routes can be hand-mangled into the correct order and then expressed as a string of hex bytes, this is onerous for DHCP administrations and error-prone.
>
> While I appreciate the option_classless_static_route.cc offers a new less error-prone way of publishing static routes, I would still expect that I can keep using the legacy old way of defining static classless routes in my config. Especially since I want to use the same config on my failover kea server that is still on Kea version 2.4.1 (stable) and can't be easily upgraded. So the Kea version 2.6.2 apparently can't use the old way, and the Kea version 2.4.1 (stable) can't use the new way of defining routes.
>
>
> I found this https://kb.isc.org/docs/kea-configuration-sections-explained documentation, but I am not sure how to use it. It seems more about defining client classes than what I need.
>
>
> Is there a way to get around the error "unable to override definition of option '121' in standard option space 'dhcp4' "?
>
>
> Best regards
>
> Mark
>
>
>
>
>
>
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