PXEBOOT confsued by dhcrelay -- two gids ?

[David W. Hankins]

Ah, I understand the problem now.

The relay is leaving giaddr set to itself (what the server set it to),
and pxeboot is ignoring the routers option in favor of the giaddr.


In RFC1542, section 3.4, we find this text:

      DISCUSSION:

         The semantics of the 'giaddr' field were poorly defined.
         Section 7.5 of [1] states:

           "If 'giaddr' (gateway address) is nonzero, then the packets
           should be forwarded there first, in order to get to the
           server."

   In that sentence, "get to" refers to communication from the client to
   the server subsequent to the BOOTP exchange, such as a TFTP session.
   Unfortunately, the 'giaddr' field may contain the address of a BOOTP
   relay agent that is not itself an IP router (according to [1],
   Section 8, fifth paragraph), in which case, it will be useless as a
   first-hop for TFTP packets sent to the server (since, by definition,
   non-routers don't forward datagrams at the IP layer).
...
   To reach a non-local server, clients can obtain a first-hop router
   address from the "Gateway" subfield of the "Vendor Information
   Extensions" [2] (if present), or via the ICMP router discovery
   protocol [5] or other similar mechanism.


Have you already taken this up with the pxeboot people?

Looking again at RFC1542 section 4.1.2:

         All BOOTP fields MUST be preserved intact.  The relay agent
         MUST NOT modify any BOOTP field of the BOOTREPLY message when
         relaying it to the client.

What you want I guess is a way to set giaddr on BOOTREPLY for these
older clients...precisely what that says you can't.

But in practice that shouldn't be dangerous, so I don't know why it
says that except no one probably thought of it at the time.

But there's no way to do it right now...no option you can set to get
this behaviour that I'm aware of.


The only real workaround I can see from my end of the problem is to
setup your relay box to ip forward.

But the pxeboot people might have better news.

-- 
David W. Hankins		"If you don't do it right the first time,
Software Engineer			you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins