dhcpd sporadically ignoring one of two "copies" of a DHCP request

Niall O'Reilly niall.oreilly at ucd.ie
Tue Mar 11 16:31:54 UTC 2014


At Tue, 11 Mar 2014 16:00:55 +0000,
Phil Mayers wrote:
> On 11/03/14 15:10, Phil Mayers wrote:
> > So: why would dhcpd sporadically ignore a 2nd DISCOVER? How can I debug
> > this?
> Bit more info: it only does this for DISCOVER messages which are using
> a dynamic lease. It doesn't do it for broadcast REQUEST, or for
> DISCOVER on a fixed-address.
> Perhaps some locking around the dynamic lease allocation?

  We have a similar network, without Juniper, and with HSRP running
  between paired routers.  We had a similar problem with clients not
  getting leases.  Once we had our OSPF costs aligned with the HSRP
  priorities, we didn't see the problem any more.  That's to say, our
  particular way of looking at the problem led us to treat it as a
  routing problem, not an ignored DISCOVER problem.

  You seem to be looking at it from the other end, and may be onto
  an aspect that we missed, but found we didn't need to address.

  I wonder whether the missing DISCOVER is actually reaching the
  server where it's being ignored, or rather has taken a path
  where it falls foul of some uRPF check.  What does packet capture

  I hope this helps.

  Best regards,
  Niall O'Reilly

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