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Re: [lwip-users] Strategy Question for DHCP

From: Robert Deschambault
Subject: Re: [lwip-users] Strategy Question for DHCP
Date: Thu, 14 May 2015 15:53:07 -0400

Thanks for the input!  I will see if it works with our system.

On Thu, May 14, 2015 at 2:55 PM, Zach Smith <address@hidden> wrote:

Use the auto ip feature of lwip which I believe is the proper way to handle this situation. With this feature enabled, after a certain number of dhcp timeouts the device will fail over to an “auto ip” address. The auto ip address is an address the device chooses for itself in the range 169.254.x.x. It will perform a quick check to see if any other device out there has the address. If so, it chooses another one and checks again. Upon finding a free address it self-configures with that address. dhcp discover messages continue to go out at some defined interval and if a dhcp server ever responds then the assigned address overwrites the previously assigned auto ip address.


Check out autoip.c (it does all this for you) and the following defines:


#define LWIP_AUTOIP                                              1  

#define LWIP_DHCP_AUTOIP_COOP                  1 //defines auto ip to work with dhcp

#define LWIP_DHCP_AUTOIP_COOP_TRIES    6 // controls how many dhcp discovers to try before timing out to an auto ip address

#define LWIP_AUTOIP_CREATE_SEED_ADDR     //lets you control the first auto ip address the device will try


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Bob Deschambault

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