[Dnsmasq-discuss] [PATCH] Delay DHCP replies for Raspberry Pi clients

Dan Sneddon dsneddon at redhat.com
Wed Mar 29 21:35:22 BST 2017

On 03/29/2017 10:43 AM, Chris Novakovic wrote:
> On 29/03/2017 18:13, Kurt H Maier wrote:
>> On Wed, Mar 29, 2017 at 02:48:48PM +0200, Floris Bos wrote:
>>> The PXE boot firmware implementation of the Raspberry Pi 3
>>> has a bug causing it to fail if it receives replies
>>> instantly.
>>> As a workaround ensure there is a minimum delay of one
>>> second if the client is a Pi.
>>> On Linux it looks up the exact receive time of the UDP
>>> packet with the SIOCGSTAMP ioctl to prevent multiple
>>> delays if multiple packets come in around the same time,
>>> or if there already was a delay caused by a ping check.
>> Why not have a configurable dhcp-delay setting instead of putting
>> device-specific quirks into the source code of dnsmasq forever?
> +1 for a dhcp-delay setting, ideally per-MAC: the Ethernet adapters on
> older RPi models (as well as the built-in wifi adapter on the RPi 3)
> also use the b8:27:eb OUI, and this artificial delay oughtn't be applied
> to them.
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Another +1 for adding a dhcp-delay setting on a per-MAC basis.

There is a side-benefit that this would enable a form of HA where you
have two servers, and one is set to have a built-in delay in its
responses. This would allow the primary server to (nearly) always
respond first if up, and the secondary server would respond after a
delay in case the first server was down.

Dan Sneddon         |  Senior Principal Software Engineer
dsneddon at redhat.com |  redhat.com/openstack
dsneddon:irc        |  @dxs:twitter

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