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Re: [lwip-users] DHCP, switch to static IP if no answer

From: Bill Auerbach
Subject: Re: [lwip-users] DHCP, switch to static IP if no answer
Date: Mon, 27 Jun 2011 09:03:14 -0400

Yes, I know it can be a problem, but it was more important that our devices
could be found quickly by a discovery program than by the (probably rare)
occurrence of a slow DHCP server.

But, you got me thinking...  it would be interesting if devices had AutoIP
addresses while waiting for the DHCP server.  Wouldn't it make sense to
provide an AutoIP address immediately to be able to talk to and/or find
devices and let the DHCP code change it when (or if) the address is


>Just for the protocol: Doing this, you might run into problems if you
>only wait 5s. RFC2131 (DHCP spec) says:
>"4.4.1 [...] The time over which the client collects messages and the
>mechanism used to select one DHCPOFFER are implementation dependent."
>Well, they don't give any numbers, but Windows/Linux/BSD all wait far
>more than 5s before giving up. Reasons might be ARP checking timeouts at
>the DHCP server wait longer before sending a DHCPOFFER.

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