Subject: TCP/IP stack initialization with DHCP client

From: "Ramkumar Perumanam" <[email-masked]>
Date: Mon, 15 May 2000 16:17:05 EDT

Hi All,
    I have a fundamental question regarding the DHCP client initialization 
with TCP/IP protocol stack. If this is a oft repeated question please bear 
with me. Here is my question.
    DHCP is based on UDP and hence requires TCP/IP stack to be setup to be 
functional(to send broadcast messages). If that's the case assuming that 
there is no IP addr yet assigned to the client, is it possible to initialize 
the TCP/IP stack without an IP addr so that DHCP can be used to obtain the 
real IP addr from a DHCP server? Once the DHCP client obtains IP addr from 
the server does the TCP/IP stack need to be reinitialized with the new IP 
addr or how does the reinitialization of TCP/IP with IP addr does not cause 
a reboot of the client machine?
    This is a theoretical question. If you answer this question with a 
practical example(say wrt a commercial implementation) that's fine with me. 
I would like to know how the catch-16 situation between IP stack 
initialization and DHCP client behavior(if at all any) is resolved?
    I really appreciate if any knowledgeable folks could clarify my doubts.

Thanks,
Ram.
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From: "Kostur, Andre" <[email-masked]>
Date: Mon, 15 May 2000 13:32:28 -0700

See RFC2131, Section 2, Page 11 (for how can UDP work with a partially
unconfigured IP stack)

Basically it depends on the behaviour of the DHCP client's IP stack that it
will accept packets destined to its MAC address, regardless of the
destination IP.  So what happens is the client starts off by broadcasting to
the world, and using 255.255.255.255 (I recall seeing Microsoft's stack
using this) as the source IP address.  As part of the DHCP packet, the
device's MAC address is included.  The DHCP servers interested in responding
either:
  1) Broadcast their replys (which a lot of IP stacks seem to accept when
unconfigured)
  2) Unicast their replys back to the origination MAC address, with the
offered IP address as the destination IP address.

Now, as for individual IP stacks and how they behave, that's up to the
implementor.  

-----Original Message-----
From: Ramkumar Perumanam [mailto:[email-masked]]
Sent: Monday, May 15, 2000 1:17 PM
To: DHCPv4 discussion list
Subject: TCP/IP stack initialization with DHCP client

Hi All,

Thanks,
Ram.