GitLab

name: Per-host subnet overrides
about: It's occasionally useful to drop an option on a one-off basis in a group

Initial Questions

If you have a configuration like:

authoritative;
log-facility daemon;
default-lease-time 3600;
max-lease-time 86400;
option domain-name "example.com";
subnet 192.168.1.0 netmask 255.255.255.0 {
 range 192.168.1.128 192.168.1.254;
 option subnet-mask 255.255.255.0;
 option broadcast-address 192.168.1.255;
 default-lease-time 43200;
 max-lease-time 43200;
 option routers 192.168.1.1;
 option domain-name-servers 192.168.1.1;
 option ntp-servers 192.168.1.40;
}

...
# and a bunch of static allocations in as "host" reservations

host switch {
 hardware ethernet 00:01:02:03:04:05;
 fixed-address 192.168.1.2;
 option host-name "switch";
}

...
# and an alarm system that should never have a default-route
host alarm {
 hardware ethernet 00:01:02:0a:0b:0c;
 fixed-address 192.168.1.8;
 option host-name "alarm";
 option routers none;
}

In this case, it's easier to default all of the hosts as getting a default-route, except for one where that isn't the case and call that out explicitly.

In the special case of IPv4 routers, you can set it to "0.0.0.0" and an ISC-DHCP client will reject this value, but the same is not true of many other DHCP clients, including the built-in one in NetworkManager, and indeed this should be handled server-side anyway ("Be conservative in what you send...").

Prior Discussion

This has been brought up on the #isc-dhcp IRC channel as well as the dhcp-workers mailing list.

Limitations/Genesis

If I have a subnet with 250 hosts, 249 of which should receive a default route, and 1 of which shouldn't, I shouldn't have to write 250 host definitions... and if I'm using dynamic allocations, this isn't even possible. Configuration should be powerful, simple, and easy.

Desired Solution Be able to override subnet defaults on a per-host basis.

Alternatives There really aren't any. Even if I were to use classes as a shorthand, I'd still need to default all hosts on my network.

Additional context None

Funding its development See below.

Participating in development I'd be willing to drive the development of this feature and do most of it myself, but I might need some guidance navigating the code base as I'm not well-versed in it.

Contacting you Comments on this issue, or as philipp@redfish-solutions.com via email, or as philipp64 on IRC (freenode.org).