[lwip-users] [lwip] Re: DHCP client to the lwIP stack

[leon . woestenberg]

Hello Michal,

I've received this message from Michal, who addressed a delicate issue in
DHCP.

Thanks for that feedbacj Michal.

> I have just downloaded and reviewed your implementation of a DHCP client
for
> the lwIP stack. In my mind a question was born. Namely, I'd like to learn
> why don't you set the BORADCAST bit in the DHCP header's field "flags"?
This
> would allow you not to do checking, which you are doing in the function
> input.c. I mean about the fragment:
>
That approach would work, and would not need the ip.c/ip_input() patch.

But it is not recommended, as per RFC1542 (referenced by RFC2131):

---
3.1.1 The BROADCAST flag

   ...
   If a client does not have this limitation (i.e., it is perfectly able
   to receive unicast BOOTREPLY messages), it SHOULD NOT set the
   BROADCAST flag (i.e., it SHOULD clear the BROADCAST flag to 0).

      DISCUSSION:

         This addition to the protocol is a workaround for old host
         implementations.  Such implementations SHOULD be modified so
         that they may receive unicast BOOTREPLY messages, thus making
         use of this workaround unnecessary.  In general, the use of
         this mechanism is discouraged.
---

So, with respect to RFC1542, I've decided to follow the recommendation
above, which I emailed to Adam through the list a week or so ago.

Adam, maybe you can add this comment to my ip.c/ip_input() patch:

/* as recommended by RFC 1542 section 3.1.1, referred by RFC 2131 */



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