On Sat, Aug 16, 2025 at 08:03:40AM +0000, Francis Dupont wrote:
> In Kea the subnet-mask (1) option is explicitely NOT in the list of
> standard DHCPv4 options configurable by an administrator so trying to
> set a value in an option-data entry does not work.
>
> So you have to use the flex option hook library to supersede the option
> value before responses are sent. I am afraid that it is the most common
> usage of this tool but it was reported to do the job by all persons
> who asked this question about how to change the netmask in this list...
Huh, I saw this as my first search hit:
https://kb.isc.org/docs/altering-the-subnet-mask-option-based-on-giaddr
and thought, that can't be the simplest way to set the client's netmask,
but I now know it is the simplest way, and this works fine:
// Allow the listening netmask to be different from the client's netmask
// https://kb.isc.org/docs/altering-the-subnet-mask-option-based-on-giaddr
"hooks-libraries": [
{
"library": "/usr/lib/x86_64-linux-gnu/kea/hooks/libdhcp_flex_option.so",
"parameters": {
"options": [
{
"name": "subnet-mask",
"supersede": "255.254.0.0"
}
]
}
}
],
> PS: there is a KB article about this but if you believe this should be
> added as an example in the ARM open a ticket in Kea gitlab.
In reading the KB article, I assume the hook was only for _computing_
the netmask, not the simplest way for a constant netmask. I was wrong.
Thanks, everything works now.
--
Bruce Momjian <[email protected]> https://momjian.us
EDB https://enterprisedb.com
Do not let urgent matters crowd out time for investment in the future.
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