expected behavior of 'static' leases/reservations with infinite-is-reserved

[Stephan Seeger]

Hi everybody,

I'm running isc-dhcp-server4.4.1 on a Ubuntu 20.04.3 LTS system in a
ddns config in conjunction with a BIND 9.16.1 and have a question
regarding the 'infinite-is-reserved' directive:

 From what I've read in the docs and various internet sources my
understanding is that setting the directive globally to 'on' in
dhcpd.conf I should be able to have host entries with 'infinite'
leasetimes that serve as 'static' leases/reservations (even) within a
dynamic range.

Respective lines in my dhcpd.conf look like this:


xxxxxxxxxxxxxxxxxx   snip   xxxxxxxxxxxxxxxxxx

...

infinite-is-reserved on;

...

subnet 172.16.1.0 netmask 255.255.255.0 {
  range 172.16.1.10 172.16.1.199;
  option subnet-mask 255.255.255.0;
  option routers 172.16.1.1;
  option broadcast-address 172.16.1.255;
  host test {
   hardware ethernet de:ad:be:ef:de:ad;
   fixed-address 172.16.1.200;
   min-lease-time 4294967295;
   max-lease-time 4294967295;
  }

...

}

xxxxxxxxxxxxxxxxxx   snip   xxxxxxxxxxxxxxxxxx


 From some source I read that these 'static' leases would be processed
by dhcpd's state engine like normal dynamic leases - but at least in my
case this doesn't seem to be true. Doing a tail -f on my servers
/var/lib/dhcp/dhcpd.leases file I was never able to have a lease
generated for host 'test' in above setting - and also not with following
modifications of the host definition:

  host test {
   hardware ethernet de:ad:be:ef:de:ad;
   fixed-address 172.16.1.200;
   min-lease-time -1;
   max-lease-time -1;
  }

...or...

  host test {
   hardware ethernet de:ad:be:ef:de:ad;
   fixed-address 172.16.1.200;
   min-lease-time 2147483647;
   max-lease-time 2147483647;
  }

Seems like the 'fixed-address' directive in the host definition prevents
the server from generating an entry in the leases-file.

Can anybody please clarify whether this is expected behavior or not or
what I'm doing wrong here and point me into the right direction?

PS: I did not verify until now but would suspect that also ddns for my
host 'test' is not possible when there's no lease generated, correct?


Best regards

Stephan