FW: DHCPDECLINE messages question

David W. Hankins David_Hankins at isc.org
Mon Oct 2 17:26:04 UTC 2006

On Mon, Oct 02, 2006 at 10:03:49AM -0400, Dennis Dufford wrote:
> We are receiving duplicate dhcp broadcasts because of a bug in the Cisco router code.
> We run Cisco routers in HSRP, but due to a code bug, the inactive HSRP router is also sending the dhcp broadcast.  This is fixed in a later version, and we intend to upgrade.  BTW: this has caused (a very few) problems in the past where, because two broadcasts were sent, and maybe the dhcp servers (or network) were busy, the failover server got a reply back to the client first, and the client ended up on the wrong address.  We have a few very picky people who want the same IP every time.  According to Murphy's law, it is these picky people who will observe this anomaly - and they did.

I don't consider this a bug.  I used to be the kind of sysop who liked
things simple and easy.  To that end, it would be my preference for
both routers to relay broadcasts, rather than trying to outsmart
themselves and only pick one router to transmit.

It's hard to imagine, but it's happened to me a few times: weird
situations where one router's unicasts to the server fail but the
other's succeed.

So if Cisco does have a feature (I'm not aware of) that lets them
silence the partner's ip-helper in an HSRP pair, I would advise
against using it.

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David W. Hankins	"If you don't do it right the first time,
Software Engineer		you'll just have to do it again."
Internet Systems Consortium, Inc.	-- Jack T. Hankins

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