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Re: [lwip-users] Multiple IP addresses

From: Leon Woestenberg
Subject: Re: [lwip-users] Multiple IP addresses
Date: Thu, 10 Jun 2004 19:14:23 +0200
User-agent: Mozilla Thunderbird 0.5 (Windows/20040207)

Hello Paul,

Paul wrote:
I have been asked to implement a dhcp assigned ip address such that if there is no dhcp server present the interface will default to a 10.0.0.x ip address. I figure I could start the dhcp code and some time later check if the
interface has an ip address or

Two things:
1) I would like to add this to lwIP, but I will do it the neat way
which will involve a netif NETIF_UP and DOWN flag.

2) If you want something that works now, the easiest thing to do is modify this piece of code in dhcp.c:

static void dhcp_timeout(struct netif *netif)
  /* back-off period has passed, or server selection timed out */
  if ((dhcp->state == DHCP_BACKING_OFF) ||
      (dhcp->state == DHCP_SELECTING)) {
  /* receiving the requested lease timed out */
  } else if (dhcp->state == DHCP_REQUESTING) {

into this:

static void dhcp_timeout(struct netif *netif)
  if ((dhcp->state == DHCP_BACKING_OFF)
    /* stop trying DHCP */
    /* fallback */
  } else if (dhcp->state == DHCP_SELECTING) {
    if (dhcp->tries <= 2) {
    } else {
      /* stop trying DHCP */
      /* fallback */

In ipconfig_fallback() configure the network interface as you like.

I am wondering if it is possible to have an interface configured for DHCP
and have a second ip address assigned to the same interface?

Not at the moment. What I would like to see implemented is this:

1) Mark the interface down.
2) *Optionally* provide an address to the interface using netif_addr()
3) If (2) did not provide an address, start ARP quering for available addresses in the address space allocated for that (like Windows does when it does not find a DHCP server). (Must lookup defacto spec...).
3) In parallel, (!) query for a DHCP server.
4) If 3 fails, fallback to 3 (or to 2 if an address was specified).

If you want to work in either area, I am interested in reviewing the
code for inclusion in the CVS source tree, but only if it is not
hackery. :-)



Or, if the

or is there a better way ?


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