Subject: [dhcwg] Link Address filed in Relay Messages

From: "punit shah" <[email-masked]>
Date: Thu, 15 Mar 2007 11:02:59 +0530

We are currently designing a s/ware that will act as a plug in for a RADIUS
Server. It will then emulate the users (who login to the NAS)
as DHCPv6 Client and the generated messages will be submitted to a Relay
Agent on the same box for transmission to a DHCPv6 Server.

The question is that DHCPv6 Servers can allocate addresses based on Link
Address field.

The RFC says Relay Agent must fill the RElay-Forward messages with a
global/site local(now deprecated) address belonging to the same
link as that of the user who needs to be allocated IPv6 address. But the
problem is our sware has no means of knowing which link (or even MAC
address) of the
user and IPv6 addresses on the users link.

Is it possible to solve this problem in a rfc compliant manner and how?

Also would link local address be acceptable or alternatively a fictitious
global address not neccesarily on the usre's l;ink?

rgds,
punith ([email-masked])
P.S.G. College of Technology, India.
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From: "David W. Hankins" <[email-masked]>
Date: Mon, 19 Mar 2007 09:55:30 +0100

> Is it possible to solve this problem in a rfc compliant manner and how?

I do not think so.

The MAC address is unimportant to a DHCPv6 server.  So long as the
DUID and IAID combine together to form one unique binding for one
unique client, the mechanics of those identifiers are irrelevant.

Not knowing at least one global address that resides on the link
the client is connected to is a big problem.

> global address not neccesarily on the usre's l;ink?

I do not think so.

I think the best you can do is fill the link address field with
zeroes and hope for the best, but this requires some very strange
DHCPv6 server configuration - where the server is expected to
know where all clients are singly attached (this is very odd for
a DHCP server...the expectation is always that they move between
networks), and can give such addresses despite lack of hints from
the relay agents.

-- 
ISC Training!  http://www.isc.org/training/  [email-masked]
Washington DC area, April 16-20 2007.  DNS & BIND, DDNS & DHCP.
-- 
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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From: "Bernie Volz \(volz\)" <[email-masked]>
Date: Mon, 19 Mar 2007 05:16:48 -0400

The link-addr field should be filled in with a global unicast address of
the interface on which the relayed request was received.

But, there may be relay agents that have no global unicast address
available to place in the link-addr field (perhaps the link on which the
client's message was received only has link-local addresses). And, what
should that relay agent put in this field then?

I do NOT think putting the link-local address for the interface is the
correct answer. If there is no global unicast address, the relay should
place the 0::0 address in the link-addr field.

I would also like to see text in a future RFC 3315 replacement that
recommends that if a server uses the link-addr value to determine where
a client is located and absent any other policy, the server should look
through the Relay-Forw messages, starting with the Relay-Forw closest to
the client (innermost) for the first non-zero link-addr field and use
that.

Note that servers can use whatever policies they want to determine the
client's "location"; thus a server is free to always use something like
the 3rd Relay-Forw's link-addr field or other options in a Relay-Forw to
determine the client's location.

- Bernie

-----Original Message-----
From: David W. Hankins [mailto:[email-masked]] 
Sent: Monday, March 19, 2007 4:56 AM
To: punit shah
Cc: [email-masked]
Subject: Re: [dhcwg] Link Address filed in Relay Messages

I do not think so.

I do not think so.

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From: "David W. Hankins" <[email-masked]>
Date: Mon, 19 Mar 2007 11:07:56 +0100

> place the 0::0 address in the link-addr field.

I agree, but I'm not sure it fits in the network being described by
punit shah.

I suspect in this network that there is a disconnect between where
a client is connected, where the radius/DHCPv6 relay is, and the
server's ability to discover the client's connection.