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

[<Hideshi.Enokihara at jp.yokogawa.com>]

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

_______________________________________________
dhcwg mailing list
dhcwg at ietf.org
https://www1.ietf.org/mailman/listinfo/dhcwg