Re: [lwip-users] DHCP and changing the MAC address

[Leon Woestenberg]

Hello Tom,

Tom C. Barker wrote:
> I have a manufacturing scenario where I need to change the
> MAC address after DHCP has come up. My code will stop_dhcp
> and then start_dhcp. If I initially zero out the ip address, 
> I get a response from my dhcp server and am up and running
> however, when the code goes to change the listening pcbs 
> for any previously running services, no pcb local addresses 
> get changed to the new dhcp-assigned addressed because the 
> interface ip was set to zero and does not match the original 
> pcb's local address. 
>
> If I do not zero the ip address prior to asking for a new
> dhcp address, (ask for a new dhcp address while I claim I
> have an address) I get no response from my dhcp server. The
> coarse timer simply keeps sending out requests every 10 seconds.
>
> Going back and forth from DHCP-off and a static IP address
> to DHCP-on performs perfectly. 
>
> Could anyone help on this issue? 
Sure.

The current way of stopping DHCP is dhcp_release() then dhcp_stop().
As solo, dhcp_stop() does not release the DHCP lease.

However, release() does exactly what you describe; it also zeroes
the netif address (see dhcp.c source code of _release).

I suggest removing these lines from dhcp_release:
  /* remove IP address from interface */
  netif_set_ipaddr(netif, IP_ADDR_ANY);
  netif_set_gw(netif, IP_ADDR_ANY);
  netif_set_netmask(netif, IP_ADDR_ANY);

and then try again using dhcp_start(), release() then stop(), then 
change MAC, then start().

Of course, that may fail still;

What is interesting to examine then, is what the failing pair of DHCP 
request/offer messages look like. (i.e. where things fail).

Can you use ethereal(.org)? You may especially look at
the dhcp.ciaddr field, source ARP and IP address.

Regards, Leon.