fixed and dynamic ip address allocation for same client

[Tarik Gasmi]

Hello,

our ISC DHCP Service is serving a campus-wide network infrastructure.

we are facing the problem to get the flexibility in ip-client-allocation
that we need:

some mobile ip-devices (notebooks, pdas, mobile-ip-phones, etc.) have a
fixed-address in one subnet, e.g. in the office, but on the other hand
they also have to receive dynamic ip addresses from lease pools in other
subnets, e.g. when the user is moving around on the campus to other
departments.

when a host is configured with a fix ip-allocation

host foo {
  hardware ethernet <foomac>;
  fixed-address ip-subnet1;
}

it gets the ip-subnet1 when connected to subnet1. but it receives no ip
address from a dynamic pool in subnet2 when connected to subnet2

subnet2 <network> <netmask> {
  ...
  pool {
    allow unknown-clients;
    <some dynamic range>;
  }
}

in the logs we get the message "DISCOVER ... peer holds all free leases"

we also tried by adding a second host declaration for the same host like

host foo-dyn {
  hardware ethernet <foomac>;
}

still not working.

we could have host declarations for the same host with fixed-addresses
of all subnets it would probably connect to. but this is not very
flexible and would cost a lot of ip addresses to be allocated fixed.

is there a way to set up a fix&dynamic ip-allocation for dhcp clients?

thank you and best regards,
tarik