Hack/modification to enforce minimum time?
Simon Hobson
dhcp1 at thehobsons.co.uk
Wed Mar 7 22:40:05 UTC 2007
Oscar Ricardo Silva wrote:
>Not sure if I'll describe this properly ... we're considering a
>modification of
>the dhcp server code to add extra time to the lease so it's completely not
>available for an amount of time after lease expiration. Before going forward
>with this we'd like to know if anyone has already worked on this or
>implemented it.
>
>We have several public networks that have a lot of churn, lots of users coming
>and going. Client A comes along, requests an address, gets address 1.2.3.4,
>the lease time is set to an hour but the client leaves after being on for only
>10 minutes so he issues a release. Let's say our accounting
>software refreshes
>its records every 20 minutes. Since Client A issued the release,
>the address is
>marked as available. Client B comes along, requests and address,
>gets 1.2.3.4.
> As far as our accounting records go, we still think Client A is
>using address
>1.2.3.4. We want to enforce the lease time (or maybe half the lease time) so
>that an address is marked as unavailable during either the lease time or half
>the lease time. That way, when client B comes along, even though address
>1.2.3.4 is marked as released, it's still in the original lease time
>so client B
>has to be assigned another address.
I think you've missed a key detail here - addresses are reused on a
least recently used basis, so if the address really is reused in
that short a time then I think you have a more serious problem ! For
this to happen, you would have to have no other expired leases which
expired earlier - which in practical terms you have virtually no free
leases. Which means, you have insufficient addresses for your
networks.
However, if you did want to implement the modification, I suspect the
simplest way to do it is to simply ignore dhcp-release messages. You
will then start getting complaints because, in the scenario above,
client B would not get an address as there wouldn't be one free.
More information about the dhcp-users
mailing list