Static IP and IP management

Glenn Satchell glenn.satchell at
Thu Feb 25 01:23:41 UTC 2016

On Thu, February 25, 2016 6:15 am, Simon Hobson wrote:
> Chuck Anderson <cra at WPI.EDU> wrote:
>> You can do that, but you have to use "reserved" leases rather than
>> fixed-address statements.  ISC dhcpd doesn't track the expiry of
>> fixed-address leases.
> To expand on that ...
> When you use a fixed-address statement to assign an address, no actual
> lease is created. Since it's a fixed address, there's no real need for it
> - so the server takes a shortcut, replies to the client, but doesn't
> actually store anything. So the only DNS update possible is when the
> "lease" is given out.
> A relatively new feature is a "reserved" lease. It acts the same as an
> ordinary lease - including normal expiry and DNS updates/removals - with
> the one difference of being tied to a single client.
> To use this feature, you need to either modify an existing lease (add the
> "reserved" statement), or you should be able to create a skeleton lease
> (including reserved statement) in advance of the client connecting.
> In either case, you probably need to be learning OMAPI to interact with
> the server !

What about not even using reserved leases, but just setting a long enough
lease time? If the lease expires then the DNS entry is removed. Next
system comes along and if that old IP is the only one available it gets

A "long enough" lease time might be a week, month or longer.

This uses DHCP for what it was designed for, and if an old device comes
back, then it will get its old address if that is still available, but it
might also just get a new one. As long as you have a good naming
convention and everything uses dns names rather than IP address it could
"just work".


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