Re: Re: Re: [Etherboot-users] [PATCH] ISC dhcpd siaddr (next-server) zero default change in 3.0.2

On Thu, Sep 15, 2005 at 06:11:23PM +0200, [email protected] wrote:
> > On Sep 14, 2005, at 7:35, Marty Connor wrote:
> >> On Sep 14, 2005, at 8:36 AM, Harald Welte wrote:
> >> 2) dhcp-3.0.2 suddenly changed the default from the dhcp server
> >> address
> >>    to 0.0.0.0.  ...
> >
    <snip/> 
> RFC2131 (http://rfc.net/rfc2131.html) says:
> >   DHCP clarifies the interpretation of the 'siaddr' field as the
> >   address of the server to use in the next step of the client's
> >   bootstrap process.  A DHCP server may return its own address in the
> >   'siaddr' field, if the server is prepared to supply the next
> >   bootstrap service (e.g., delivery of an operating system executable
> >   image).

Thanks for posting  it here ( I didn't have time to review RFC 2131 )

> So the main question is: What is meant by "next step of the client's
> bootstrap process"?

Example given: Delivery of an operating system executable.

> I guess the correct behavior would be using 'siaddr' for the TFTP-Server
> but not for the DHCP-Server. I don't think it would make sense to send
> DHCPREQUEST (Reply to DHCPOFFER) to the server in 'siaddr' which could
> be another machine than the sender of DHCPOFFER. This message should
> IMHO always be sent to the DHCP-Server in 'server identifier'.
> 
> Later, after finishing DHCP, the next step in the bootstrap process
> is TFTP. So 'siaddr' should be used here.
> 
> This is necessary if the DHCP and the TFTP server are different
> hardware.

And having those servers on different hardware does happen.

> What is not mentioned in the RFC is the behavior if 'siaddr' is set to
> zero. Either the bootstrap process should be aborted then, or the DHCP
> server could be asked if it also provides bootimages by TFTP.

Please implement the proposal that was posted in another message

 Drop the DHCP offer and wait for DHCP offer that a non-zero siaddr.

> I think defaulting to the DHCP server is much more convenient.

And I think it is a lie to say in a poor configurated DHCP server
that the same hardware is also a TFTP server. The right thing is
to tell in the DHCP server where the TFTP server is.

From the manual page of ISC DHCP server:

      next-server server-name;

      The next-server statement is used to specify the host address of
      the server from which the initial boot file (specified in the file-
      name  statement) is to be loaded. Server-name should be a numeric
      IP address or a domain name.


So doing the right thing is this time easy  :-)


> Thanks for your great work!

You are welcome.

> Bye, Max


St

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