RE: [dhcwg] [Question] When should we use Interface-ID option

["Bernie Volz \(volz\)" <volz at cisco.com>]

Hideshi:

If a relay agent (which is a router) terminates a bunch of circuits, it
may well be that each of those circuits does not have their own unique
prefix (and hence a link-addess field that can be used). For example, a
relay may have one global address for all of these circuits.

In such a case, the relay must know on which circuit to relay any
replies from a server, and hence the interface-id can be used.

- Bernie

-----Original Message-----
From: Hideshi.Enokihara at jp.yokogawa.com
[mailto:Hideshi.Enokihara at jp.yokogawa.com] 
Sent: Friday, October 06, 2006 3:43 AM
To: dhcwg at ietf.org
Subject: [dhcwg] [Question] When should we use Interface-ID option

Hi all,

I have a question regarding Interface-ID option in DHCPv6.

RFC3315 defines Interface-ID option, 
but I cannot understand in what situation this option should be used. 

RFC3315 20.1.1 says,
----------
(snip)
   If the relay agent cannot use the address in the link-address field
   to identify the interface through which the response to the client
   will be relayed, the relay agent MUST include an Interface-id option
   (see section 22.18)
(snip)
----------

I cannot imagine above sentence situation.
I mean that I can't think up the situation("Relay agent cannot use the
address 
in the link-address field to identify the interface")

Someone, please teach me the situation that Relay agent should use
Interface-ID option in detail.

Moreover, I can't understand actual meaning of following statement.
#I feel the RFC is unclear regarding Interface-id option usage.
--------------
20.1.1. Relaying a Message from a Client
   (snip)	
 
                                                                     The
   relay agent fills in the link-address field as described in the
   previous paragraph regardless of whether the relay agent includes an
   Interface-id option in the Relay-forward message.
---------------
In this statement, when a Relay agent includes an Interface-id option,
what should the Relay agent fill in the link-address field?

What do you think?

Best Regards,

*************************************
Hideshi Enokihara
IPv6 Business
Network & Software Development Dept.
Yokogawa Electric Corporation

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