padding before end of DHCPOFFER packet?

Joseph Bernard jhb at
Mon Sep 8 13:18:50 UTC 2014

That is exactly the same issue.  I’m working with Cisco 3560X switches that replace Option 82 with padding.  The old Jetdirects refuse to handle the padding at all.  I did some testing by tweaking the DHCP packets, and it wouldn’t even accept a single pad that was within the spec.

Joseph B.

On Sep 5, 2014, at 5:35 PM, Christian Kratzer <ck-lists at> wrote:

> Hi,
> On Thu, 4 Sep 2014, Joseph Bernard wrote:
>> Is it valid to have padding (0) before the end (255) of a DHCPOFFER packet?  I have a Cisco switch doing this, but I’m not sure if it valid.  I have some old HP Jetdirect boxes that will not take a packet constructed like this.  I just want to be sure if the padding is valid or not so I don’t mistakingly accuse Cisco of having bad code.
> I saw this when a customer upgraded their Cisco4500 from Sup6 with IOS to Sup7 with IOS XE.
> The padding was from the cisco removing option82 information before passing the packet back to the client. IOS squeezed the space out of the packet. IOS XE poked padding over the deleted regions.
> Zyxel MES2110 switches choked on this but Zyxel provided an updated firmare.
> Greetings
> Christian
> -- 
> Christian Kratzer                   CK Software GmbH
> Email:   ck at               Wildberger Weg 24/2
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