From the ISC web site [LWN.net]

From the ISC web site

Posted May 29, 2025 20:54 UTC (Thu) by bferrell (subscriber, #624)
Parent article: Local vulnerabilities in Kea DHCP

ISC has developed a new DHCP server, Kea, which we intend to replace ISC DHCP in most server implementations. We recommend that new implementers use Kea and implement ISC DHCP only if Kea does not meet their needs. The Kea distribution does not currently include either a client or a relay. Anyone interested in underwriting the development of a DHCP client or relay is encourage to contact ISC at info@isc.org.

So... Suse selected a not yet complete project and wrote up the flaws.

The good news is that dhcpcd (used mostly in debian based distros at one time) wasn't used by default. I've not done a modern deb install in a while so it may still be in use.

I spent a full 36 hours troubleshooting an odd behavior... If ISC dhcp is set to send extra routes, the last extra route ends up the default route for dhcpcd. A lot of fiddling with ISC dhcpd will get dhcpcd to work right... But then it breaks dhcp in iphones, android devices, "smart" plugs and Windows.

The machines that caused me to look into it (raspberry pi) got dhcpcd yanked and the ISC dhcp client installed.

Yes, I DID discuss it with the dev and gave up. It does faithfully support an obscure RFC. But the RFC is broken (as far as I'm concerned).

to post comments

From the ISC web site

Posted May 29, 2025 21:23 UTC (Thu) by rschroev (subscriber, #4164) [Link] (9 responses)

The other text on the page were you got that is:

"ISC has announced the end of maintenance for ISC DHCP as of the end of 2022. ISC will continue providing professional support services for existing subscribers, but does not intend to issue any further maintenance releases. For resources that may help in migrating your existing ISC DHCP server deployment to our newer DHCP server, Kea, please see this page.

ISC DHCP was a complete open source solution for implementing DHCP servers, relay agents, and clients."

Clearly the ISC really wants you to use Kea instead of ISC DHCP server. You don't want to run network software that hasn't been maintained since 2022.

It does feel weird that ISC doesn't have a client or relay agent anymore. Did people migrate to other solutions?

From the ISC web site

Posted May 30, 2025 9:43 UTC (Fri) by jengelh (subscriber, #33263) [Link]

>Did people migrate to other solutions?

I migrated to IPv6/SLAAC :-p
NetworkManager has its own client. And some people might have gone with udhcp or systemd-networkd.

From the ISC web site

Posted May 30, 2025 10:08 UTC (Fri) by joib (subscriber, #8541) [Link] (4 responses)

There's dhcpcd (used in Ubuntu initramfs, presumably Debian and other Debian-based distros as well). Not sure what other distros are using for initramfs needs. And NetworkManager as well as systemd-networkd have their own internal clients, which I guess is what most distros are using by default.

I'm not aware of any maintained open source relay agent. One particular brand of switches I'm aware of hasn't migrated off isc dhcp relay, presumably the vendor is supporting it themselves.

From the ISC web site

Posted May 30, 2025 16:46 UTC (Fri) by auerswal (subscriber, #119876) [Link] (1 responses)

Dnsmasq (https://dnsmasq.org/doc.html) contains DHCP relay functionality, is available under the GPL, version 2 or version 3, and maintained.

From the ISC web site

Posted May 30, 2025 18:38 UTC (Fri) by joib (subscriber, #8541) [Link]

Oh! I'm familiar with dnsmasq, but I didn't realize it provides dhcp relay functionality as well. Thanks!

From the ISC web site

Posted Jun 1, 2025 13:18 UTC (Sun) by bferrell (subscriber, #624) [Link] (1 responses)

from my previous post:

The machine that prompted me to investigate (a Raspberry Pi) had dhcpcd removed and the ISC DHCP client installed.

Yes, I DID discuss it with the dev and gave up. It does faithfully support an obscure RFC. But the RFC is broken (as far as I'm concerned).

From the ISC web site

Posted Jun 2, 2025 15:18 UTC (Mon) by hmh (subscriber, #3838) [Link]

This is interesting... can you post some details? a link to a bug report, or the reference to the "obscure RFC", etc ?

From the ISC web site

Posted May 30, 2025 13:13 UTC (Fri) by Sesse (subscriber, #53779) [Link]

I believe you can use Kea itself as a relay agent (though not a client).

OpenBSD dhcpd?

Posted May 30, 2025 14:52 UTC (Fri) by DemiMarie (subscriber, #164188) [Link]

Is that still maintained?

From the ISC web site

Posted Jun 4, 2025 0:02 UTC (Wed) by fratti (subscriber, #105722) [Link]

> Clearly the ISC really wants you to use Kea instead of ISC DHCP server. You don't want to run network software that hasn't been maintained since 2022.

You are talking to a Debian user. They only run software that hasn't been maintained since 2022.

From the ISC web site

Posted May 30, 2025 18:33 UTC (Fri) by gherkin (guest, #177675) [Link]

There's quite a lot of interesting background/historical info on the ISC site, touching on both Kea and ISC DHCP, and their history, for example the blog article announcing the EoL for ISC DHCP (https://www.isc.org/blogs/isc-dhcp-eol/) - which points to a lot of the reasons why Kea was developed, and notes the following from one of the ISC DHCP maintainers:

"The relay was never really popular - people mostly used their ethernet switches features for relaying - but it provided value by being a “tool in the toolbox” so to speak, useful in a pinch."

And the relay and client functionality was EoL'd from ISC DHCP about a year and a half before the rest of the project, so it's perhaps understandable that ISC saw little demand for that functionality in Kea from their sponsors and other funding sources.

https://www.isc.org/dhcphistory/ was interesting too, particularly Kea's origins in BIND 10.

(Given the links to BIND 10, and that era at ISC, I'd suspect that there are probably some fun bits of history that didn't make it past the PR machine ;) )