Your Discuss on draft-ietf-dhc-subscriber-id

[Ralph Droms <rdroms@cisco.com>]

Bert - I see that you had a Discuss on draft-ietf-dhc-subscriber-id:

  An AAA-doctor reviewed this and has a question:

    This document looks good. One question: There seems to be a
    growing number of identifiers (client-id etc) for users in
    the DHCP space. Is there some rule set to determine which of
    the attributes and in which order are used when, say,
    determining if the same or different IP address should be
    handed to the client? For instance, if the client-id has
    changed but the subscriber ID stays the same, what do you
    do? Or is this all left to policy?

  Do we have an answer?

I also see that your position is now "No-objection".  Just to be clear, the
subscriber-id sub-option is an identifier for a subscriber that is supplied
by the DHCP relay agent, based on the logical port to which that subscriber
is attached, and not an identifier for a specific device (which is what the
client-id identifies, as supplied by the DHCP client) or for a user (DHCP
doesn't have a user identifier, per se).  So, while the subscriber-id is yet
another identifier, it does not overlap the function of the existing
client-id or MAC address identifiers.  The subscriber-id is not supplied by
the DHCP client and requires no configuration support in the client.

The circuit ID and remote ID relay agent sub-options are close in function
to the subscriber-id sub-option.  The motivation for the subscriber-id is to
provide late binding between the subscriber and the identifier tag, so
changes in the subscriber port assignment can be made without reprogramming
the DHCP server. This function is useful in the case where the subscriber
connection management is in a different administrative domain from the DHCP
server (e.g., MSO owns the subscriber connection, ISP runs the DHCP server).

In any event, policy in the DHCP server governs the use of the various
values in the DHCP options and relay agent sub-options to determine the IP
address assignment, accounting and other provisioning.  For example, an ISP
DHCP server would likely use the subscriber-id sub-option to identify the
subscriber to which a device belongs and the client-id to identify which of
the subscriber's devices is initiating the DHCP message exchange.

- Ralph