Re: [dhcwg] dhcpv6-24: Interface-ID option

[Ralph Droms <[e-mail]>]

At 11:09 AM 5/8/2002 -0400, Thomas Narten wrote:
> >    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 forwarded, the relay agent MUST include an Interface-id
> >    option (see section 22.19) in the Relay-forward message.  The server
>
>I think the interface-id option may be underspecified. If it is
>included, but there is no valid link-address (which I understand is
>the reason for defining this particular option), how does the server
>know which addresses to assign the client? I.e., how does the server
>know on which link the client is?

The relay agent always fills in the link-address field even if it also 
includes an Interface-id option.  Does the text need to be clarified?


> >    The relay agent puts the client's address in the link-address field
> >    regardless of whether the relay agent includes an Interface-id option
> >    in the Relay-forward message.
>
>This doesn't seem right to me. I thought that the link-address is
>supposed to hold the address of the relay agent. Seems wrong to put
>the client's address in it. The link-address field is what the server
>uses to figure out which link the client is on (right?). Also, since
>the client's address is a link-local address, this field doesn't seem
>to contain useful information for the server in this case.

This text should be edited to (based on suggested text from Bernie):

    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.


> >    Servers MAY use the Interface-ID for parameter assignment policies.
> >    The Interface-ID SHOULD be considered an opaque value, with policies
> >    based on exact string match only; that is, the Interface-ID SHOULD
> >    NOT be internally parsed by the server.
>
>Shouldn't the first MAY be a MUST? I.e., the link-address field
>contains no useful information.

The link-address field does contain useful information (a site-scoped or 
global address); the Interface-ID provides additional information.

>Also, not sure the above is sufficient. Unless the
>interface-identifier is somehow stable, it's not clear how the server
>policy could take it into account. There are no words suggesting the
>interface-identifier needs to be stable.

OK, we'll add some words about stability.


> >       interface-id         An opaque value of arbitrary length generated
> >                            by the relay agent to identify one of the
> >                            relay agent's interfaces
>
>Any reason not to make this 32 bits? the IPv6 API already has 32-bit
>interface IDs. Is there any reason to make it larger?

The relay agent may use another value aside from the IPv6 API for the
interface-id, so we should allow for arbitrary length.

- Ralph



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