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Re: MVP for a DHCP server (was Re: ISC's EoL dhcp suite, including dhcpd)
---- On Mon, 14 Jul 2025 17:28:11 +0100 Martin Husemann <martin%duskware.de@localhost> wrote ---
> On Mon, Jul 14, 2025 at 04:53:01PM +0100, Roy Marples wrote:
> > Why do you need to wire hosts to fixed IP addresses?
>
> Several different reasons, the DNS entry is one of them - think about
> printers that others need to reach over the network for example.
> I am not sure if the old printer devices would work with mDNS.
>
> Putting them outside the dynamic range should work (actually that is how
> I run them currently, but I have way more then 10 non-dynamic IPs).
>
> The other reason is the NFS server has hardwired permissions mapping root
> file systems to IP addresses. So a diskless client mounting its / via NFS
> needs a fixed IP and needs DHCP. I am not sure what you mean with the
> INFORM variant.
>
> And then there are "smart" devices where turning off DHCP does not
> always work so you have to give them a fixed IP via DHCP and matching
> firewall rules. The most popular variant of this is devices allowing
> a fixed IPv4 configuration but then doing IPv6 auto configuration
> w/o any option to disable IPv6 completely.
Would you consider an option to use ethers(5) for this instead?
This would allow IPv4 mapping, but not IPv6.
MVP I guess would be IP address only, no idea how hard it would be to make a DNS call to work out the IP address if it's a hostname.
>
> > This is an important question because there is no equivalent for DHCPv6 as DHCPv6 does not carry a hardware address option.
> > DHCPv6 and DHCPv4 Client ID MUST be treated as opaque values
>
> Opaque value is fine, as long as I can note it in my config somehow.
> No need to only allow this via MAC address.
>
> > Even Infiniband with DHCP has this issue because the hardware address does not fit inside the chaddr field and needs to use a Client ID.
> > https://gitlab.isc.org/isc-projects/kea/-/issues/3331
> >
> > My view is that if you need a host to be a fixed IP address then
> > please configure the fixed IP address on the host and use the INFORM
> > function.
>
> I don't know how you configure INFORM only (but I could look that up). This
> is OK, but having central ways to update those devices to slightly changed
> network settings is very convenient. This clearly is a corner case.
in dhcpcd.conf
interface bge0
inform 192.168.1.12/24
The address is optional - if missed dhcpcd will use the first one on the interface.
Roy
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