DHCP "static" assignments

Simon Hobson dhcp1 at thehobsons.co.uk
Fri Aug 9 14:09:10 UTC 2013

Alex Moen wrote:
>> * Watch out for bootp clients and abandoned leases. Both tie up an address "forever" and can deplete your pool of free addresses. IIRC addresses leased to bootp clients are never returned to free, and abaondoned addresses are only recovered when there's nothing else left.
>Ummm... This innocent and unassuming little comment is quite unsettling.

Aren't all those little "BTW ..." comments like that ?

>We have been running ISC BIND in our ISP business for well over 15 
>years, and I have never known this little tidbit of information (you 
>never quit learning!). It seems that this is a possible resource sucker 
>that we should at least be able to enumerate and understand the impact of.
>Is there an easy way to audit the lease file, to find those addresses 
>that are abandoned and those that are tied up by a BOOTP lease, and 
>release them back to the available pool?

It's a long time since I looked, but I think bootp clients are flagged with "bootp", and abandoned leases are flagged as "abandoned" - both in the lease structures in the leases file.

You can prevent bootp clients getting a lease with "deny bootp" IIRC. The reason their leases never end is because bootp doesn't have an endtime in the protocol - so there is no way for the server to know if the client is still active or not.

More information about the dhcp-users mailing list