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

From: Claudius Zingerli
Subject: Re: [lwip-users] DHCP, switch to static IP if no answer
Date: Sat, 25 Jun 2011 00:11:06 +0200
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv: Gecko/20101207 Lightning/1.0b2 Thunderbird/3.1.7


On 2011-06-22 16:01 PM, Bill Auerbach wrote:

I used dhcp_start and then checked in a loop netif_is_up for a
connection for 5 seconds. If the 5 seconds ran out, I used dhcp_stop,
netif_set_down, netif_set_addr, netif_set_up, and dhcp_inform to set a
static IP address.

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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