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

From: Ralph Droms <[email-masked]>
Date: Thu, 16 May 2002 08:21:10 -0400 (EDT)

Original comment:

> 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 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.

> 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.

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.

>    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?

Response:

Clarified text in 20.1 to emphasize that relay agent fills in link-address
field regardless of whether Interface-ID option is used.

Added text explaining why interface-identifier for an interface should
remain stable.

Left interface-id as variable-length value.

*** dhcpv6.tty	Wed May 15 22:43:36 2002
- --- dhcpv6-24.txt	Tue Apr 23 15:35:14 2002
***************
*** 3199,3207 ****
     will be forwarded, the relay agent MUST include an Interface-id
     option (see section 22.19) in the Relay-forward message.  The server
     will include the Interface-id option in its Relay-reply message.
!    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.

     The relay agent copies the source address from the IP datagram
     in which the message was received from the client into the
- --- 3260,3268 ----
     will be forwarded, the relay agent MUST include an Interface-id
     option (see section 22.19) in the Relay-forward message.  The server
     will include the Interface-id option in its Relay-reply message.
!    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.

     The relay agent copies the source address from the IP datagram
     in which the message was received from the client into the
***************
*** 4548,4558 ****
     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.  The Interface-ID value for
!    an interface SHOULD be stable and remain unchanged, for example,
!    after the relay agent is restarted; if the Interface-ID changes, a
!    server will not be able to use it reliabily in parameter assignment
!    policies.

  22.20. Reconfigure Message option
- --- 4646,4652 ----
     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.

  22.20. Reconfigure Message option
------- End of forwarded message -------

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