Inconsistent renews from F/O peers

Simon Hobson dhcp1 at
Mon May 11 16:02:19 UTC 2015

Mark Sandrock <sandrock at> wrote:

>      it sometimes happens that shortly
> after obtaining an initial lease of MCLT,
> (3600 seconds), some Windows clients
> send a broadcast renew request that
> is responded to differently by the two
> failover peers.

> Although this seems incorrect behavior
> on the switch'es part, the pathological
> behavior of Windows renewing a lease
> only 3 seconds into it, also seems wrong.

When this happens, do you have any indication how long it took to get the reply back to the client ?
I'm wondering if a combination of factors (delay by the server, delay by the switch (I assume that the DHCP packets are being handled by the management CPU)) are leading to a delay at the client which is long enough for it to retry - hence the second renew after 3 seconds.

You may need to leave a packet capture running until you capture an event. IIRC there is a field (who's name escapes me at the moment) in the packet which indicates how long the client has been trying - if the first packet has 0 and the second has 3, then this would seem to support the hypothesis.

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