DHCP "static" assignments

Steven Carr sjcarr at gmail.com
Thu Aug 8 09:59:34 UTC 2013

On 8 August 2013 08:08, Simon Hobson <simon at thehobsons.co.uk> wrote:
> And lastly, sorry lost who wrote that you can have the fixed-address within a pool and it's OK. No you cannot, it is NOT OK.
> Any fixed addresses must **NOT** be in any dynamic range<period>. Certain safety features may (or these days, more likely may not) help you, but if you overlap the config like this then there is a good chance that eventually the server will attempt to hand out the same address to two clients.
> The main thing that will stop this is the "ping before lease" feature. IFF the client with the fixed address is online AND it responds to pings AND you haven't disabled the ping before lease function AND this is an initial offer rather than a renewal, then the server will detect this (it gets a ping reply from that address) and mark the dynamic lease as abandoned. Abandoned leases are only use in the last resort when all other leases are in use - so it would possibly appear to the casual observer that "there's no problem".
> Remove any of those conditions and you risk getting a duplicate address allocation on your network - which is considered "not good".

My bad, I was under the impression that DHCPD knew that the
fixed-address was the owner of the address and so wouldn't hand out a
pool address to a dynamic client (as it was already owned).


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