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

From: <[email-masked]>
Date: Fri, 6 Oct 2006 16:42:42 +0900

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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---

From: Anthony Baire <[email-masked]>
Date: Fri, 13 Oct 2006 17:51:18 +0200

Hi Hideshi and all,

I am also wondering how the Interface-Id field should be used practically.

RFC3315 is quite clear about how to use it for routing Relay-Reply
messages back to the client. But the rfc is evasive about how to use it
in practice, especially how to integrate it into the address assignment
process.

RFC3315 says servers can use the link-address field for identifying to
which link the client is attached so as to assign a suitable ipv6
address. However when a relay-forward message carries an Interface-Id
option, the link-address field is undefined[1]  but the server may still
process it. The outcome is undefined and the rfc does not address this
issue.

What do others think about this ?

Do people here actually use the Interface-Id option ? if yes, which
policy is used for assigning ipv6 addresses to the clients ?

Regards

--
Anthony Baire
INRIA/IRISA - ARMOR Project

[1]  as it is suggested in your message: rfc says the field must be
filled but does not say which value should be used.