Document: draft-korhonen-mip4-service-06
Reviewer: Spencer Dawkins
Review Date: 2008-12-02
IETF LC End Date: 2008-12-24
IESG Telechat date: (not known)

Summary: This draft is on the right track for publication as Informational (should it be standards-track, if you're expecting this to be widely deployed? But I'll leave that to the IESG).

I do have comments, especially involving 2119 language.

Comments:

(Can Jouni's e-mail address really be
   Email: jouni.nospam@gmail.com
?)

1.  Introduction

   This document describes a Service Selection Extension for Mobile IPv4
   that is intended to assist home agents to make specific service
   selections for the mobility service subscription during the
   registration procedure.  The service selection may affect home agent
   routing decisions, Home Address assignment policies, firewall
   settings, and security policies.  The Service Selection extension
   SHOULD be used in every Registration Request that makes a new
   registration to the home agent.  The Service Selection extension from
   the Registration Request MAY be echoed back in the Registration
   Reply.

Spencer: I don't usually see 2119 normative language in the introduction of Internet Drafts... at a minimum, these statements appear before the requirements key words are introduced in section 2. I THINK most of these requirements are restated later in the document anyway, so they could probably be dropped here.

   In absence of a specifically indicated service the home agent MUST
   act as if the default service, plain Internet access had been
   requested.  There is no absolute requirement that this default
   service be allowed to all subscribers, but it is highly RECOMMENDED
   in order to avoid having normal subscribers employ operator-specific
   configuration values in order to get basic service.

   Some of the potential use-cases were listed earlier in this section.
   The general aim is better manageability of services and service
   provisioning from both operators and service providers point of view.
   However, it should be understood that there are potential deployment
   possibilities where selecting a certain service may restrict
   simultaneous access to other services from an user point of view.
   For example, services may be located in different administrative
   domains or external customer networks that practice excessive
   filtering of inbound and outbound traffic.

Spencer: I wasn't clear on who this understanding is directed to - it almost reads like you're warning users that bad things might happen if you use a specific service, but surely the user specifies the service because an operator requires this?

3.  Service Selection Extension

   At most one Service Selection extension MAY be included in any Mobile
   IPv4 Registration Request message.  It SHOULD be included at least in

Spencer: seems to be missing a qualifier: "When a non-default service is selected, the Service Selection extension SHOULD be included ..."?

Spencer: If this is qualified, could the SHOULD be a MUST?

Spencer: If it remains as SHOULD, what happens if the Service Selection extension is not included in the initial binding registration, but is included in subsequent binding registrations?

   the Registration Request message that is sent for the initial binding
   registration when the mobile node and the home agent do not have an
   existing binding.  The Service Selection extension MUST be placed in
   the Registration Request message as follows:

   o  When present the extension MUST appear after the MN-NAI extension,
      if the MN-NAI is also present in the message

   o  If the extension was added by the mobile node to a Registration
      Request it MUST appear prior any authentication-enabling
      extensions [RFC3344][RFC4721]

Spencer (editorial): s/prior/before/ or s/prior/prior to/

   o  In the event the foreign agent adds the Service Selection
      extension to a Registration Request, the extension MUST appear
      prior to any Foreign-Home authentication-enabling extensions
      [RFC3344]

4.1.  Mobile Node Considerations

   A mobile node or its proxy representative MAY include the Service
   Selection extension into any Registration Request message.  The
   Service Selection extension can be used with any mobile node
   identification method.  The extension is used to identify the service
   to be associated with the mobility session and SHOULD only be

Spencer: this seems to be more restrictive than previous text that allowed the extension to be included in non-initial registration request messages...

   included into the initial Registration Request message sent to a home
   agent.  If the mobile node wishes to change the selected service, it
   is RECOMMENDED that the mobile node de-register the existing binding

Spencer: why RECOMMENDED and not REQUIRED? RECOMMENDED means that home agents must handle the case where the SHOULD isn't observed anyway.

   with the home agent before proceeding with a binding registration for
   a different service.  The provisioning of the service identifiers to
   the mobile node or its proxy representative is out of scope of this
   specification.

6.  IANA Considerations

   A new Mobile IPv4 skippable Extension type is required for the
   following new Extension described in Section 3.  The Extension type
   must be from the 'skippable Extension' range (128-255):

       Service Selection Extension       is set to TBD

   A new Mobile IPv4 registration denied by home agent error code is
   required.  The error code must be allocated from the 'Error Codes
   from the Home Agent' range (128-192):

       SERVICE_AUTHORIZATION_FAILED      is set to TBD

Spencer: (if you revise this draft, you probably want to use "TBD1", "TBD2", etc. so that it's clearer to IANA which "TBD" gets replaced with each allocated value)