PXEBOOT confsued by dhcrelay -- two gids ?
David W. Hankins
David_Hankins at isc.org
Thu Apr 6 00:42:08 UTC 2006
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
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