helpfor option ping-check

Gregory Sloop gregs at
Thu Jun 27 00:49:22 UTC 2013

Do you have logs showing these duplicate leases occurring by ISC-DHCPd?

I'd be surprised to see such a thing - but if it really is happening
as you think, I believe it should be in the DHCP logs - showing the
request and offer and ack/nak of the first host, then then the
request, offer and ack/nak of the second host for the same IP.

Could you dig these out and let us see them?

As far as ping-check - if the DHCP server *really is* handing out
duplicates, then I can't imagine ping-check would prevent that - since
it the DHCP server that's misbehaving and one more check certainly
isn't certain to fix another massive flaw in the DHCP server.

To be clear, I'm doubtful the DHCP server *is* working incorrectly, but
if it is, then ping-check isn't likely to fix a DHCP server that's so
badly borked.

But in any case, seeing logs showing the duplicate dynamic assignment
would seem like the best place to start.


JX> The problem is between two machines who are in dynamic pool, no of them in reserved area.

JX> -----Original Message-----
JX> From: Doug Barton [mailto:dougb at] 
JX> Sent: Thursday, 27 June 2013 10:33 AM
JX> To: Users of ISC DHCP
JX> Cc: Julie Xu
JX> Subject: Re: helpfor option ping-check

JX> On 06/26/2013 05:16 PM, Julie Xu wrote:
>> If I do not use check ping, do I have anyway to fix pool problem? Or do I need check something else on the reason?

JX> Julie,

JX> The only real way to solve this problem is to make sure that your
JX> pools don't include already issued static addresses. The usual way
JX> to do this is to have part of the network reserved for statics,
JX> and start the pool outside of that range. If you have existing
JX> static addresses scattered throughout the network that cannot be
JX> changed for some reason you can create lots of little pools that
JX> are split around those static addresses. The other possible
JX> solution is to create DHCP reservations for the already-assigned
JX> static addresses, but that doesn't really solve your management problem long-term.

JX> Unfortunately, there is no "easy" solution to this problem, your
JX> organization needs to be a little more proactive in your network management.

JX> hope this helps,

JX> Doug

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