DHCP peer failure and pool exhaustion...

Steven Carr sjcarr at gmail.com
Mon Sep 9 18:14:08 UTC 2013

On 9 September 2013 18:50, Gregory Sloop <gregs at sloop.net> wrote:
> So, does that sound right?

Yes, your assumptions are correct, it sounds like the peer ran out of
leases from it's side of the pool.

> If so, is there any way to "automagically" put the peer in partner
> down state if it's not able to be contacted in X amount of time?

No, and that's generally a bad thing to do, that type of DR scenario
should not be automated as it could be triggered accidentally by a
number of situations.

> Or, perhaps I should simply say - I don't want the DHCP server to end
> up without available addresses to lease, if the peer goes off-line and
> I'm not able to do some manual process to intervene. That's my goal.
> With that goal in mind, what's the best way to accomplish it?

There is no way on the DHCP side that would resolve your current
situation. The easiest way is to fix the network side of things,
increase the number of IPs you have in the pools by increasing the
size of the networks or add additional networks to cope with your

It also seems that you have a high churn rate of clients, without
enough IPs if they all came online at once. Your leases are being
recycled and not reused by the same client repeatedly so when you get
a spike there is no existing expired lease that the client can grab a
hold of so you end up depleting the remaining half pool quickly.

You should calculate the pools to ensure that there is enough IPs for
all the clients, plus some buffer space to allow for a host to fail. I
would usually size the pool at 120-150% of the number of clients
depending on the size of the subnet to start with.


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