MIF Working Group                                         D. Anipko, Ed.
Internet-Draft                                     Microsoft Corporation
Intended status: Informational                             July 03, 2014
Expires: January 02, 2015

               Multiple Provisioning Domain Architecture


   This document is a product of the work of MIF architecture design
   team.  It outlines a solution framework for some of the issues,
   experienced by nodes that can be attached to multiple networks.  The
   framework defines the notion of a Provisioning Domain (PVD) - a
   consistent set of network configuration information, and PVD-aware
   nodes - nodes which learn PVDs from the attached network(s) and/or
   other sources and manage and use multiple PVDs for connectivity
   separately and consistently.

Status of this Memo

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   This Internet-Draft will expire on January 02, 2015.

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   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights

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   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
   2.  Definitions and types of PVDs  . . . . . . . . . . . . . . . .  4
     2.1.  Explicit PVDs  . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Implicit PVDs and incremental adoption of the explicit PVDs 5
     2.3.  Relationship between PVDs and interfaces . . . . . . . . .  6
     2.4.  PVD identity/naming  . . . . . . . . . . . . . . . . . . .  6
     2.5.  Relationship to dual-stack networks  . . . . . . . . . . .  7
     2.6.  Elements of PVD  . . . . . . . . . . . . . . . . . . . . .  7
   3.  Conveying PVD information using DHCPv6 and Router Advertisement 7
     3.1.  Separate messages or one message . . . . . . . . . . . . .  8
     3.2.  Securing the PVD information . . . . . . . . . . . . . . .  8
     3.3.  Backward compatibility . . . . . . . . . . . . . . . . . .  8
     3.4.  Selective propagation  . . . . . . . . . . . . . . . . . .  8
     3.5.  Retracting/updating PvD information  . . . . . . . . . . .  9
     3.6.  Conveying configuration information using IKEv2  . . . . .  9
   4.  Example network configurations and number of PVDs  . . . . . .  9
     4.1.  A mobile node  . . . . . . . . . . . . . . . . . . . . . .  9
     4.2.  A node with a VPN connection . . . . . . . . . . . . . . . 10
     4.3.  A home network and a network operator with multiple PvDs . 11
   5.  Reference model of PVD-aware node  . . . . . . . . . . . . . . 12
     5.1.  Constructions and maintenance of separate PVDs . . . . . . 12
     5.2.  Consistent use of PVDs for network connections . . . . . . 13
       5.2.1.  Name resolution  . . . . . . . . . . . . . . . . . . . 13
       5.2.2.  Next-hop and source address selection  . . . . . . . . 14
       5.2.3.  Listening applications . . . . . . . . . . . . . . . . 14  Processing of incoming traffic . . . . . . . . . . 15
   Connection-oriented APIs . . . . . . . . . . . 15
   Connection-less APIs . . . . . . . . . . . . . 15
       5.2.4.  Enforcement of security policies . . . . . . . . . . . 15
     5.3.  Connectivity tests . . . . . . . . . . . . . . . . . . . . 16
     5.4.  Relationship to interface management and connection manage 16
   6.  PVD support in APIs  . . . . . . . . . . . . . . . . . . . . . 17
     6.1.  Basic  . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     6.2.  Intermediate . . . . . . . . . . . . . . . . . . . . . . . 17
     6.3.  Advanced . . . . . . . . . . . . . . . . . . . . . . . . . 18
   7.  PVD-aware nodes trust to PVDs  . . . . . . . . . . . . . . . . 18
     7.1.  Untrusted PVDs . . . . . . . . . . . . . . . . . . . . . . 18
     7.2.  Trusted PVDs . . . . . . . . . . . . . . . . . . . . . . . 18
       7.2.1.  Authenticated PVDs . . . . . . . . . . . . . . . . . . 19
       7.2.2.  PVDs trusted by attachment . . . . . . . . . . . . . . 19
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     11.1.  Normative References  . . . . . . . . . . . . . . . . . . 20
     11.2.  Informative References  . . . . . . . . . . . . . . . . . 20

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   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21

1.  Introduction

   Nodes attached to multiple networks may encounter problems due to
   conflict of the networks configuration  and/or simultaneous use of
   the multiple available networks.  While existing implementations
   apply various techniques ([RFC6419]) to tackle such problems, in many
   cases the issues may still appear.  The MIF problem statement
   document [RFC6418] describes the general landscape as well as
   discusses many specific issues and scenarios details.

   Problems, enumerated in [RFC6418], can be grouped into 3 categories:

   1.  Lack of consistent and distinctive management of configuration
       elements, associated with different networks.

   2.  Inappropriate mixed use of configuration elements, associated
       with different networks, in the course of a particular network
       activity / connection.

   3.  Use of a particular network, not consistent with the intent of
       the scenario / involved parties, leading to connectivity failure
       and / or other undesired consequences.

   An example of (1) is a single node-scoped list of DNS server IP
   addresses, learned from different networks, leading to failures or
   delays in resolution of names from particular namespaces; an example
   of (2) is use of an attempt to resolve a name of a HTTP proxy server,
   learned from a network A, with a DNS server, learned from a network
   B, that is likely to fail; an example of (3) is use of an employer-
   sponsored VPN connection for peer-to-peer connectivity, unrelated to
   employment activities.

   This architecture describes a solution to these categories of
   problems, respectively, by:

   1.  Introducing a formal notion of the PVD, including PVD identity,
       and ways for nodes to learn the intended associations among
       acquired network configuration information elements.

   2.  Introducing a reference model for a PVD-aware node, preventing
       inadvertent mixed use of the configuration information, which may
       belong to different PVDs.

   3.  Providing recommendations on PVD selection based on PVD identity
       and connectivity tests for common scenarios.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",

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   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Definitions and types of PVDs

   Provisioning Domain: a consistent set of network configuration
   information.  Classically, the entire set available on a single
   interface is provided by a single source, such as network
   administrator, and can therefore be treated as a single provisioning
   domain.  In modern IPv6 networks, multihoming can result in more than
   one provisioning domain being present on a single link.  In some
   scenarios, it is also possible for elements of the same domain to be
   present on multiple links.

   Typical examples of information in a provisioning domain, learned
   from the network, are: source address prefixes that can be used by
   connections within the provisioning domain, IP address of DNS server,
   name of HTTP proxy server if available, DNS suffixes associated with
   the network, default gateway address etc.

   PVD-aware node: a node that supports association of network
   configuration information into PVDs, and using these PVDs to serve
   requests for network connections in ways, consistent with
   recommendations of this architecture.

2.1.  Explicit PVDs

   A node may receive explicit information from the network and/or other
   sources, about presence of PVDs and association of particular network
   information with a particular PVD.  PVDs, constructed based on such
   information, are referred to in this document as "explicit".

   Protocol changes/extensions will likely be required to support the
   explicit PVDs by IETF-defined mechanisms.  As an example, one could
   think of one or several DHCP options, carrying PVD identity and / or
   its elements.  A different approach could be to introduce a DHCP
   option, which only carries identity of a PVD, while the association
   of network information elements with that identity, is implemented by
   the respective protocols - such as e.g., with a Router Discovery
   [RFC4861] option associating an address range with a PVD.

   Specific, existing or new, features of networking protocols to enable
   delivery of PVD identity and association with various network
   information elements will be defined in companion design documents.

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   Link-specific and/or vendor-proprietary mechanisms for discovery of
   PVD information, different from the IETF-defined mechanisms, can be
   used by the nodes separately from or together with IETF-defined
   mechanisms, as long as they allow to discover necessary elements of
   the PVD(s). Another example of a delivery mechanism for PVDs are key
   exchange or tunneling protocols, such as  IKEv2 [RFC5996] that allow
   transporting host configuration information.  In all cases, by
   default nodes must ensure that the lifetime of all dynamically
   discovered PVD configuration is appropriately limited by the relevant
   events - for example, if an interface media state change was
   indicated, the previously discovered information may no longer be
   valid and needs to be re-discovered or confirmed.

   It is expected, that how the node makes use of the PVD information,
   generally is independent of the specific particular mechanism/
   protocol that was used to receive the information.

   It shall be possible for sources of PVD information to communicate
   that some of their configuration elements could be used within a
   context of other networks/PVDs.  PVD-aware nodes, based on such
   declaration and their policies, may choose to inject such elements
   into some or all other PVDs they connect to.

   In some network topologies, the network infrastructure elements may
   need to advertise multiple PVDs.  The details of how this is done
   generally will be defined in the individual companion design
   documents.  However, where different design choices are possible, the
   choice that requires smaller number of packets shall be preferred for

2.2.  Implicit PVDs and incremental adoption of the explicit PVDs

   It is likely that for a long time there may be networks which do not
   advertise explicit PVD information, since deployment of any new
   features in networking protocols is a relatively slow process.

   When connected to networks, which don't advertise explicit PVD
   information, PVD-aware node shall automatically create separate PVDs
   for received configuration.  Such PVDs are referred to in this
   document as "implicit".

   With implicit PVDs, PVD-aware nodes may still provide benefits to
   their users as compared to non-PVD aware nodes, by using network
   information from different interfaces separately and consistently to
   serve network connection requests, following best practices described
   in Section 5.

   In the mixed mode, where e.g., multiple networks are available on the
   link the interface is attached to, and only some of the networks
   advertise PVD information, the PVD-aware node shall create explicit
   PVDs based on explicitly learned PVD information, and associate the
   rest of the configuration with an implicit PVD created for that

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2.3.  Relationship between PVDs and interfaces

   By default, implicit PVDs are limited to network configuration
   information received on a single interface.  If additional
   information is available to the host through mechanisms out of scope
   of this document, the host may form implicit PVDs with different
   granularity, such as e.g.  spanning multiple interfaces (an example
   scenario, where this may be useful, is a Homenet with a router that
   has multiple internal interfaces).

   Explicit PVDs, in practice will often also be scoped to a
   configuration related to a particular interface, however per this
   architecture there is no such requirement or limitation and as
   defined in this architecture, explicit PVDs may include information
   related to more than one interfaces, if the node learns presence of
   the same PVD on those interfaces and the authentication of the PVD ID
   meets the level required by the node policy (generally,
   authentication of a PVD ID may be also required in scenarios,
   involving only one connected interface and/or PVD).

   It is an intent of this architecture to support such scenarios among
   others.  Hence, it shall be noted that no hierarchical relationship
   exists between interfaces and PVDs: it is possible for multiple PVDs
   to be simultaneously accessible over one interface, as well as single
   PVD to be simultaneously accessible over multiple interfaces.

2.4.  PVD identity/naming

   For explicit PVDs, PVD ID (globally unique ID, that possibly is
   human-readable) is received as part of that information.  For
   implicit PVDs, the node assigns a locally generated with a high
   probability of being globally unique ID to each implicit PVD.

   PVD-aware node may use these IDs to choose a PVD with matching ID for
   special-purpose connection requests, in accordance with node policy
   or choice by advanced applications, and/or to present human-readable
   representation of the IDs to the end-user for selection of Internet-
   connected PVDs.

   A single network provider may operate multiple networks, including
   networks at different locations.  In such cases, the provider may
   chose whether to advertise single or multiple PVD identities at all

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   or some of those networks, as it suits their business needs.  This
   architecture doesn't impose specific requirements in this regard.

   When multiple nodes are connected to the same link, where one or more
   explicit PVDs are available, this architecture assumes that the
   information about all available PVDs is advertized by the networks to
   all the connected nodes.  At the same time, the connected nodes may
   have different heuristics, policies and/or other settings, including
   configured set of their trusted PVDs, which may lead to different
   PVDs actually being used by different nodes for their connections.

   Possible extensions, where different sets of PVDs may be advertised
   by the networks to different connected nodes, are out of scope of
   this document.

2.5.  Relationship to dual-stack networks

   When applied to dual-stack networks, the PVD definition allows for
   multiple PVDs to be created, where each PVD contain information for
   only one address family, or for a single PVD that contains
   information about multiple address families.  This architecture
   requires that accompanying design documents for the PVD-related
   protocol changes must support PVDs containing information from
   multiple address families.  PVD-aware nodes must be capable of
   dealing with both single-family and multi-family PVDs.

   For explicit PVDs, the choice of either of the approaches is a policy
   decision of a network administrator and/or node user/administrator.
   Since some of the IP configuration information that can be learned
   from the network can be applicable to multiple address families (for
   instance DHCP address selection option [RFC7078]), it is likely that
   dual-stack networks will deploy single PVDs for both address

   For implicit PVDs, by default PVD-aware nodes shall including
   multiple IP families into single implicit PVD created for an
   interface.  At the time of writing of this document in dual-stack
   networks it appears to be a common practice for configuration of both
   address families to be provided by a single source.

   A PVD-aware node that provides API to use / enumerate / inspect PVDs
   and/or their properties shall provide ability to filter PVDs and/or
   their properties by address family.

2.6.  Elements of PVD

3.  Conveying PVD information using DHCPv6 and Router Advertisements

   DHCPv6 and Router Advertisements are the two most common methods of
   configuring hosts and they would need to be extended to convey
   explicit PVD information.  There are several things that need to be
   considered before finalizing a mechanism to augment DHCPv6 and RAs
   with PvD information.

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3.1.  Separate messages or one message

   When information from several PVDs is available at the same
   configuration source, there are two possibilities regarding how to
   send these out.  One way is to send information from different
   provisioning domains in separate messages.  The other is to combine
   information from several PVDs onto one message.  The latter method
   has the advantage of being more efficient but could have issues due
   to authentication and authorization issues as well as potential
   issues with accommodating common information and information not
   tagged with any PVD information.

3.2.  Securing the PVD information

   DHCPv6 and RAs both provide some form of authentication that ensures
   the identity of the source as well as the integrity of the contents
   that have been secured.  While this is useful, the authenticity of
   the information provides no information whether the configuration
   source is actually allowed to provide information from a given PVD.
   In order to do be able to do this, there must be a mechanism for the
   owner of the PVD to attach some form of authorization token to the
   configuration information that is delivered.

3.3.  Backward compatibility

   The extensions to RAs and DHCPv6 should be defined in such a manner
   than unmodified hosts (i.e.  hosts not aware of PvDs) will continue
   to function as well as they did before the PvD information got added.
   This could imply that some information may need to be duplicated in
   order to be conveyed to legacy hosts.  Similarly PvD aware hosts need
   to be able to handle legacy configuration sources which do not
   provide PvD information.  There are also several initiatives ongoing
   that are aimed at adding some form of additional information to
   prefixes [refs to draft-bhandari and draft-korhonen] and any new
   mechanism should try to consider co-existence with these existing

3.4.  Selective propagation

   When a configuration source has information regarding several PvDs it
   is not clear whether it should provide information about all of them
   to any host that requests info from it.  While it may be reasonable
   in some cases, this might become an unreasonable burden once the
   number of PvDs starts increasing.  One way to restrict the
   propagation of useless information is for the host to select the PvD
   information they desire in their request to the configuration source.
   One way this could be accomplished is by using an ORO with the PvDs
   that are of interest.  The configuration source can then respond with
   only the requested information.

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   By default, a configuration source SHOULD provide information related
   to all provisioning domains without expecting the client to request
   the PvD(s) it requires.  This is necessary to ensure that hosts that
   do not support requesting selective PvD information will continue to
   work.  Also note that IPv6 neighbor discovery does not provide any
   functionality analogous to the DHCPv6 ORO.

   In this case, when a host receives PvD information it does not
   require, the information can simply be discarded.  Also, in
   constrained networks such as LLNs, the amount of configuration
   information needs to be restricted to ensure that the load on the
   hosts is bearable while keeping the information identical across all
   the hosts.

   In case selective propogation is required, some form of PvD discovery
   mechanism needs to be specified so that hosts/applications can be
   pre-provisioned to request a specific PvD. Alternately, the set of
   PvDs that the network can provide to the host can be propogated to
   the host using RAs or stateless DHCPv6. The discovery mechanism may
   potentially support the discovery of available PvDs on a per-host

3.5.  Retracting/updating PvD information

   After the PvD information is provided to the host it may be outdated
   or updated with newer information before the hosts would normally
   request updates.  Thos would require the mchanism to be able to
   update and/or withdraw all (or some subset) of information related to
   a given PvD. For efficiency reasons, there should be a way to specify
   that all the information from the PvD needs to be reconfigured
   instead of individually updating each item associated with the PvD.

3.6.  Conveying configuration information using IKEv2

   Internet Key Exchange protocol version 2 (IKEv2) [RFC5996] [RFC5739]
   is another widely used and a popular method of configuring IP
   information in a host.  In the case of IKEv2 the provisioning domain
   could actually be implicitly learnt from the Identification -
   Responder (IDr) payloads the IKEv2 initiator and the responder inject
   during the IKEv2 exchange.  The IP configuration may depend on the
   named IDr.  Another possibility could be adding specific provisioning
   domain identifying payload extensions to IKEv2. All of the
   considerations listed above for DHCPv6 and RAs potentialy apply to
   IKEv2 as well.

4.  Example network configurations and number of PVDs

4.1.  A mobile node

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   As an example, consider a mobile node that has two network
   interfaces: one is a mobile network interface, the other is a Wi-Fi
   network interface.  When the mobile node connects only to the mobile
   network, it will typically have one PvD, implicit or explicit.  Then
   when the mobile node discovers and connects to a Wi-Fi network, it
   will have zero or more (typically - one) additional PvD(s).

   Some of the existing OS implementations only allow one active network
   connection.  In that case, only the PVD(s) associated with that
   interface will be connected PvD at any given time.

   As an example, the mobile network can explicitly deliver the PvD
   information through the PDP context activation process.  Then the PvD
   aware mobile node will treat the mobile network as an explicit PvD.
   Conversely, the legacy Wi-Fi network may not explicitly communicate
   the PvD information to the mobile node.  The PvD aware mobile node
   will treat the network configuration of the Wi-Fi network as
   associated with an implicit PvD in this case.

   The following diagram illustrates the use of different PvDs in this

                            <------      Wi-Fi 'Internet' PvD  ------>
                   | +----+ |    +----+         _   __              _  _
                   | |WiFi| |    |    |        ( `    )            ( `   )_
                   | |-IF +-|----+    |--------------------------(         `)
                   | |    | |    |WiFi|      (         )        (_ Internet  _)
                   | +----+ |    | AP |     (           )         `- __  _) -
                   |        |    |    |    (  Service    )
                   |        |    +----+    (  Provider's   )
                   |        |              (   Networks    -
                   | +----+ |               `_            )           _  _
                   | |CELL| |                (          )           ( `   )_
                   | |-IF +-|-------------------------------------(         `)
                   | |    | |                (_     __)          (_ Internet  _)
                   | +----+ |                 `- --               `- __  _) -
                            <------- Mobile 'Internet' PvD ----------->

           An example PvD use with Wi-Fi and mobile interfaces.

4.2.  A node with a VPN connection

   If the node has established a VPN connection, zero or more (typically
   - one) additional PvD(s) will be created.  These may be implicit or
   explicit PvD(s).  The routing to the IP addresses within this PvD
   will be set up via the VPN connection, and the routing to addresses
   outside the scope of this PvD will remain unaffected.  If there were
   already N connected PvDs on the node prior to establishing VPN

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   connection, once a VPN session is connected typically the number of
   PvDs will become N+1.

   The following diagram illustrates the use of different PvDs in this

                   <------      'Internet' PvD       ------>
           | +----+ |    +----+         _   __              _  _
           | |Phy | |    |    |        ( `    )            ( `   )_
           | |-IF +-|----+    |--------------------------(         `)
           | |    | |    |    |      (         )        (_ Internet  _)
           | +----+ |    |    |     (           )         `- __  _) -
           |        |    |Home|    (  Service    )             ||
           |        |    |gate|    (  Provider's   )           ||
           |        |    |-way|    (   Network     -           ||
           | +----+ |    |    |    `_            )        +---------+  +------------+
           | |VPN | |    |    |      (          )         |   VPN   |  |            |
           | |-IF +-|----+    |---------------------------+ Gateway |--+  Private   |
           | |    | |    |    |       (_     __)          |         |  |  Services  |
           | +----+ |    +----+         `- --             +---------+  +------------+
                   <-------------  Explicit 'VPN' PvD ----------->

                       An example PvD use with VPN.

4.3.  A home network and a network operator with multiple PvDs

   An operator may use separate PvDs for individual services which they
   offer to their customers.  This may be used so that services can be
   designed and provisioned to be completely independent of each other
   allowing for complete flexibility in combinations of services which
   are offered to customers.

   From the perspective of the home network and the node, this model is
   functionally very similar to being multihomed to multiple upstream
   operators: Each of the different services offered by the service
   provider is its own PvD with associated PvD information.  In this
   case, the operator may provide a generic/default PvD (explicit or
   implicit), which provides Internet access to the customer.
   Additional services would then be provisioned as explicit PvDs for
   subscribing customers.

   The following diagram illustrates this, using video-on-demand as a
   service-specific PvD:

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                        <------ Implicit 'Internet' PvD ------>
                   +----+     +----+         _   __              _  _
                   |    |     |    |        ( `    )            ( `   )_
                   | PC +-----+    |--------------------------(         `)
                   |    |     |    |      (         )        (_ Internet  _)
                   +----+     |    |     (           )         `- __  _) -
                              |Home|    (  Service    )
                              |gate|    (  Provider's   )
                              |-way|    (   Network     -
                   +-----+    |    |    `_            )        +---------+
                   | Set |    |    |      (          )         |ISP Video|
                   | Top +----+    |---------------------------+on Demand|
                   | Box |    |    |       (_     __)          | Service |
                   +-----+    +----+         `- --             +---------+
                         <-- Explicit 'Video-on-Demand' PvD -->

                 An example PvD use with a homet network.

   In this case, the number of PVDs that a single operator could
   provision is based on the number of independently provisioned
   services which they offer.  Some examples may include:

   o  Real-time packet voice

   o  Streaming video

   o  Interactive video (n-way video conferencing)

   o  Interactive gaming

   o  Best effort / Internet access

5.  Reference model of PVD-aware node

5.1.  Constructions and maintenance of separate PVDs

   It is assumed that normally, configuration information contained in a
   single PVD, shall be sufficient for a node to fulfill a network
   connection request by an application, and hence there should be no
   need to attempt to merge information across different PVDs.

   Nevertheless, even when a PVD lack some parts of the configuration,
   merging of information from different PVD(s) shall not be done
   automatically, since typically it would lead to issues described in

   A node may use other sources, such as e.g., node local policy, user
   input or other mechanisms, not defined by IETF, to either construct a
   PVD entirely (analogously to static IP configuration of an
   interface), or supplement with particular elements all or some PVDs
   learned from the network, or potentially merge information from

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   different PVDs, if such merge is known to the node to be safe, based
   on explicit policies.

   As an example, node administrator could inject a not ISP-specific DNS
   server into PVDs for any of the networks the node could become
   attached to.  Such creation / augmentation of PVD(s) could be static
   or dynamic.  The particular implementation mechanisms are outside of
   the scope of this document.

5.2.  Consistent use of PVDs for network connections

   PVDs enable PVD-aware nodes to use consistently a correct set of
   configuration elements to serve the specific network requests from
   beginning to end.  This section describes specific examples of such
   consistent use.

5.2.1.  Name resolution

   When PVD-aware node needs to resolve a name of the destination used
   by a connection request, the node could decide to use one, or
   multiple PVDs for a given name lookup.

   The node shall chose one PVD, if e.g., the node policy required to
   use a particular PVD for a particular purpose (e.g.  to download an
   MMS using a specific APN over a cellular connection).  To make the
   choice, the node could use a match of the PVD DNS suffix or other
   form of PVD ID, as determined by the node policy.

   The node may pick multiple PVDs, if e.g., they are general purpose
   PVDs providing connectivity to the Internet, and the node desires to
   maximize chances for connectivity in Happy Eyeballs style.  In this
   case, the node could do the lookups in parallel, or in sequence.
   Alternatively, the node may use for the lookup only one PVD, based on
   the PVD connectivity properties, user choice of the preferred
   Internet PVD, etc.

   In either case, by default the node uses information obtained in a
   name service lookup to establish connections only within the same PVD
   from which the lookup results were obtained.

   For simplicity, when we say that name service lookup results were
   obtained from a PVD, what we mean is that the name service query was
   issued against a name service the configuration of which is present
   in a particular PVD.   In that sense, the results are "from" that
   particular PVD.

   Some nodes may support transports and/or APIs, which provide an
   abstraction of a single connection, aggregating multiple underlying
   connections.  MPTCP [RFC6182] is an example of such transport
   protocol.  For the connections provided by such transports/APIs, a
   PVD-aware node may use different PVDs for servicing of that logical

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   connection, provided that all operations on the underlying
   connections are done consistently within their corresponding PVD(s).

5.2.2.  Next-hop and source address selection

   For the purpose of this discussion, let's assume the preceding name
   lookup succeeded in a particular PVD.  For each obtained destination
   address, the node shall perform a next-hop lookup among routers,
   associated with that PVD. As an example, such association could be
   determined by the node via matching the source address prefixes/
   specific routes advertized by the router against known PVDs, or
   receiving explicit PVD affiliation advertized through a new Router
   Discovery [RFC4861] option.

   For each destination, once the best next-hop is found, the node
   selects best source address according to the [RFC6724] rules, but
   with a constraint that the source address must belong to a range
   associated with the used PVD. If needed, the node would use the
   prefix policy from the same PVD for the best source address selection
   among multiple candidates.

   When destination/source pairs are identified, then they are sorted
   using the [RFC6724] destination sorting rules and the prefix policy
   table from the used PVD.

5.2.3.  Listening applications

   Consider a host, connected to several PVDs and running an application
   that opens a listening socket/transport API object, where the
   application authorized by the host policy to use a subset connected
   PVDs, that may or may not be equal to the complete set of the
   connected PVDs.  For example, in case there are different PVDs on a
   Wi-Fi and a cellular interfaces, for general internet traffic the
   host could decide to use only one preferred PVD at a time (and
   accordingly, advertise to remote peers the host name and addresses
   associated with that PVD), or it could decide to use one PVD as a
   preferred one by default for outgoing connections, while still
   allowing use of the other PVDs simultaneously.  Another example is
   where a host established a VPN connection.  Depending on the security
   policies provisioned on the host, all or some applications may or may
   not be allowed to use the VPN PVD and/or other PVDs.

   For non-PVD aware applications, the OS policies determine the
   authorized set of PVDs and the preferred outgoing PVD.  For PVD-aware
   applications, both the authorized set of PVDs and the default
   outgoing PVD can be determined as a meet of the subset produced by
   the OS policies and the set of PVD IDs or characteristics, provided

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   by the application.  The application input could be provided on per-
   application, per-transport-API-object or per-transport-API-call
   basis.  The API for application input may have an option for to
   specify whether the input should be treated as a preference instead
   of a requirement.  Processing of incoming traffic

   Unicast IP packets are received on a specific IP address, associated
   with a PVD.  For multicast packets, the host can derive the
   association with a PVD from other configuration information, such as
   an explicit PVD property or local policy.

   The node OS or middleware may apply more advanced techniques for
   determination of the resultant PVD and/or authorization of the
   incoming traffic.  Those techniques are outside of scope of this

   If the determined receiving PVD of the packet is not in the allowed
   subset of PVDs for the particular app/transport API object, the
   packet should be handled in the same way as if there were no
   listener.  Connection-oriented APIs

   For connection-oriented APIs, when the initial incoming packet is
   received, the packet PVD is remembered for the established
   connection, and used for handling of the outgoing traffic for that
   connection.  While typically the connection-oriented APIs use
   connection-oriented transport protocol, such as TCP, it is possible
   to have a connection-oriented API, which uses generally connection-
   less transport protocol, such as UDP.  For APIs/protocols, which
   support multiple IP traffic flows associated with a single transport
   API connection object (such as e.g.  multi path TCP), the processing
   rules may be adjusted accordingly.  Connection-less APIs

   For connection-less APIs, the host should provide an API, which PVD-
   aware applications could use to query the PVD associated with the
   packet.  For outgoing traffic on this transport API object, the OS
   should use the selected outgoing PVDs, determined as described above.

5.2.4.  Enforcement of security policies

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   PVDs by themselves don't define and can't be used for communication
   of security policies.  When implemented in a network, this
   architecture provides the host with information about the connected
   networks.  The actual behavior of the host then depends on the host
   policies (provisioned through mechanisms out of scope of this
   document), applied taking received PVD information into account.  In
   some scenarios, such as e.g . VPN, such policies could require the
   host to use only a particular VPN PVD for some/all of the
   applications' traffic (VPN 'disable split tunneling' also known as
   'force tunneling' behavior), or apply such restrictions only to
   select applications and allow simultaneous use of the VPN PVD
   togetheer with the other connected PVDs by the other or all
   applications (VPN 'split tunneling' behavior).

5.3.  Connectivity tests

   Although some PVDs may appear as valid candidates for PVD selection
   (e.g.  good link quality, consistent connection parameters, etc.),
   they may provide limited or no connectivity to the desired network or
   the Internet.  For example, some PVDs provide limited IP connectivity
   (e.g., scoped to the link or to the access network), but require the
   node to authenticate through a web portal to get full access to the
   Internet.  This may be more likely to happen for PVDs, which are not
   trusted by the given PVD-aware node.

   An attempt to use such PVD may lead to limited network connectivity
   or connection failures for applications.  To prevent the latter, a
   PVD-aware node may perform connectivity test for the PVD, before
   using it to serve network connection requests of the applications.
   In current implementations, some nodes do that, for instance, by
   trying to reach a dedicated web server (e.g., see [RFC6419]).

   Per Section 5.2, a PVD-aware node shall maintain and use multiple
   PVDs separately.  The PVD-aware node shall perform connectivity test
   and, only after validation of the PVD, consider using it to serve
   application connections requests.  Ongoing connectivity tests are
   also required, since during the IP session, the end-to-end
   connectivity could be disrupted for various reasons (e.g.  poor L2,
   IP QoS issues); hence a connectivity monitoring function is needed to
   check the connectivity status and remove the PVD from the set of
   usable PVDs if necessary.

   There may be cases where a connectivity test for PVD selection may be
   not appropriate and should be complemented, or replaced, by PVD
   selection based on other factors.  This could be realized e.g., by
   leveraging some 3GPP and IEEE mechanisms, which would allow to expose
   some PVD characteristics to the node (e.g.  3GPP Access Network
   Discovery and Selection Function (ANDSF) [TS23.402], IEEE 802.11u

5.4.  Relationship to interface management and connection managers

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   Current devices such as mobile handsets make use of proprietary
   mechanisms and custom applications to manage connectivity in
   environments with multiple interfaces and multiple sets of network
   configurations.  These mechanisms or applications are commonly known
   as connection managers [RFC6419].

   Connection managers sometimes rely on policy servers to allow the
   node, connected to multiple networks, perform the network selection.
   They can also make use of routing guidance from the network (e.g.
   3GPP ANDSF [TS23.402]).  Although connection managers solve some
   connectivity problems, they rarely address the network selection
   problems in a comprehensive manner.  With proprietary solutions, it
   is challenging to present a coherent behaviour to the end user of the
   device, as different platforms present different behaviours even when
   connected to the same network, with the same type of interface, and
   for the same purpose.

6.  PVD support in APIs

   In all cases changes in available PVDs must be somehow exposed,
   appropriately for each of the approaches.

6.1.  Basic

   Applications are not PVD-aware in any manner, and only submit
   connection requests.  The node performs PVD selection implicitly,
   without any otherwise applications participation, and based purely on
   node-specific administrative policies and/or choices made by the user
   in a user interface provided by the operating environment, not by the

   As an example, such PVD selection can be done at the name service
   lookup step, by using the relevant configuration elements, such as
   e.g., those described in [RFC6731].  As another example, the PVD
   selection could be done based on application identity or type (i.e.,
   a node could always use a particular PVD for a VOIP application).

6.2.  Intermediate

   Applications indirectly participate in selection of PVD by specifying
   hard requirements and soft preferences.  As an example, a real time
   communication application, intending to use the connection for
   exchange of real time audio/video data, may indicate a preference or
   a requirement for connection quality, which could affect PVD
   selection (different PVDs could correspond to Internet connections
   with different loss rates and latencies). Another example is a
   connection of an infrequently executed background activity, which
   checks for availability of applications updates and performs large
   downloads - for such connections, a cheaper or zero cost PVD may be
   preferrable, even if such connection will have a higher relative loss
   rate or lower bandwidth.  The node performs PVD selection, based on
   applications inputs and policies and/or user preferences.  Some / all
   properties of the resultant PVD may be exposed to applications.

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6.3.  Advanced

   PVDs are directly exposed to applications, for enumeration and
   selection.  Node polices and/or user choices, may still override the
   application preferences and limit which PVD(s) can be enumerated and/
   or used by the application, irrespectively of any preferences which
   application may have specified.  Depending on the implementation,
   such restrictions, imposed per node policy and/or user choice, may or
   may not be visible to the application.

7.  PVD-aware nodes trust to PVDs

7.1.  Untrusted PVDs

   Implicit and explicit PVDs for which no trust relationship exists are
   considered untrusted.   Only PVDs, which meet the requirements in
   Section 7.2, are trusted; any other PVD is untrusted.

   In order to avoid various forms of misinformation that can be
   asserted when PVDs are untrusted, nodes that implement PVD separation
   cannot assume that two explicit PVDs with the same identifier are
   actually the same PVD.  A node that did make this assumption would be
   vulnerable to attacks where for example an open Wifi hotspot might
   assert that it was part of another PVD, and thereby might draw
   traffic intended for that PVD onto its own network.

   Since implicit PVD identifiers are synthesized by the node, this
   issue cannot arise with implicit PVDs.

   Mechanisms exist (for example, [RFC6731]) whereby a PVD can provide
   configuration information that asserts special knowledge about the
   reachability of resources through that PVD.   Such assertions cannot
   be validated unless the node has a trust relationship with the PVD;
   assertions of this type therefore must be ignored by nodes that
   receive them from untrusted PVDs.   Failure to ignore such assertions
   could result in traffic being diverted from legitimate destinations
   to spoofed destinations.

7.2.  Trusted PVDs

   Trusted PVDs are PVDs for which two conditions apply.   First, a
   trust relationship must exist between the node that is using the PVD
   configuration and the source that provided that configuration; this
   is the authorization portion of the trust relationship.   Second,
   there must be some way to validate the trust relationship.   This is
   the authentication portion of the trust relationship.   Two
   mechanisms for validating the trust relationship are defined.

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   It shall be possible to validate the trust relationship for all
   advertised elements of a trusted PVD, irrespectively of whether the
   PVD elements are communicated as a whole, e.g.  in a single DHCP
   option, or separately, e.g.  in supplementary RA options.  Whether or
   not this is feasible to provide mechanisms to implement trust
   relationship for all PVD elements, will be determined in the
   respective companion design documents.

7.2.1.  Authenticated PVDs

   One way to validate the trust relationship between a node and the
   source of a PVD is through the combination of cryptographic
   authentication and an identifier configured on the node.   In some
   cases, the two could be the same; for example, if authentication is
   done with a shared secret, the secret would have to be associated
   with the PVD identifier.   Without a (PVD Identifier, shared key)
   tuple, authentication would be impossible, and hence authentication
   and authorization are combined.

   However, if authentication is done using some public key mechanism
   such as a TLS cert or DANE, authentication by itself isn't enough,
   since theoretically any PVD could be authenticated in this way.   In
   addition to authentication, the node would need to be configured to
   trust the identifier being authenticated.  Validating the
   authenticated PVD name against a list of PVD names configured as
   trusted on the node would constitute the authorization step in this

7.2.2.  PVDs trusted by attachment

   In some cases a trust relationship may be validated by some means
   other than described in Section 7.2.1, simply by virtue of the
   connection through which the PVD was obtained.   For instance, a
   handset connected to a mobile network may know through the mobile
   network infrastructure that it is connected to a trusted PVD, and
   whatever mechanism was used to validate that connection constitutes
   the authentication portion of the PVD trust relationship.
   Presumably such a handset would be configured from the factory, or
   else through mobile operator or user preference settings, to trust
   the PVD, and this would constitute the authorization portion of this
   type of trust relationship.

8.  Acknowledgements

   This document was created as a product of a MIF architecture design
   team and includes contributions from the MIF working group

9.  IANA Considerations

   This memo includes no request to IANA.

10.  Security Considerations

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   There are at least three different form of attacks that can be
   performed using configuration sources that use multiple provisioning

   Tampering with configuration information provided An attacker may
      attempt to modify the information provided inside the PVD
      container option.  These attacks can easily be prevented by using
      the message integrity features provided by the underlying protocol
      used to carry the configuration information.  e.g.  SEND [RFC3971]
      would detect any form of tampering with the RA contents and the
      DHCPv6 [RFC3315] AUTH option that would detect any form of
      tampering with the DHCPv6 message contents.  This attack can also
      be performed by a compromised configuration source by modifying
      information inside a specific , in which case the mitigations
      proposed in the next subsection may be helpful.

   Rogue configuration source A compromised configuration source such as
      a router or a DHCPv6 server may advertise information about PvDs
      that it is not authorized to advertise.  e.g.  A coffee shop may
      advertise configuration information purporting to be from an
      enterprise and may try to attract enterprise related traffic.  The
      only real way to avoid this is that the PvD related configuration
      container contains embedded authentication and authorization
      information from the owner of the PvD. Then, this attack can be
      detected by the client by verifying the authentication and
      authorization information provided inside the PVD container option
      after verifying its trust towards the PvD owner (e.g.  a
      certificate with a well-known/common trust anchor).

   Replay attacks A compromised configuration source or an on-link
      attacker may try to capture advertised configuration information
      and replay it on a different link or at a future point in time.
      This can be avoided by including some replay protection mechanism
      such as a timestamp or a nonce inside the PvD container to ensure
      freshness of the provided information.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

11.2.  Informative References

              IEEE, "IEEE Standard 802.11u-2011 (Amendment 9:
              Interworking with External Networks)", 2011.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and
              M. Carney, "Dynamic Host Configuration Protocol for IPv6
              (DHCPv6)", RFC 3315, July 2003.

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   [RFC3971]  Arkko, J., Kempf, J., Zill, B. and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W. and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC5739]  Eronen, P., Laganier, J. and C. Madson, "IPv6
              Configuration in Internet Key Exchange Protocol Version 2
              (IKEv2)", RFC 5739, February 2010.

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y. and P. Eronen, "Internet
              Key Exchange Protocol Version 2 (IKEv2)", RFC 5996,
              September 2010.

   [RFC6182]  Ford, A., Raiciu, C., Handley, M., Barre, S. and J.
              Iyengar, "Architectural Guidelines for Multipath TCP
              Development", RFC 6182, March 2011.

   [RFC6418]  Blanchet, M. and P. Seite, "Multiple Interfaces and
              Provisioning Domains Problem Statement", RFC 6418,
              November 2011.

   [RFC6419]  Wasserman, M. and P. Seite, "Current Practices for
              Multiple-Interface Hosts", RFC 6419, November 2011.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A. and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012.

   [RFC6731]  Savolainen, T., Kato, J. and T. Lemon, "Improved Recursive
              DNS Server Selection for Multi-Interfaced Nodes", RFC
              6731, December 2012.

   [RFC7078]  Matsumoto, A., Fujisaki, T. and T. Chown, "Distributing
              Address Selection Policy Using DHCPv6", RFC 7078, January

              3GPP, "3GPP TS 23.402; Architecture enhancements for non-
              3GPP accesses; release 12", .

Author's Address

   Dmitry Anipko, editor
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA 98052

   Phone: +1 425 703 7070
   Email: dmitry.anipko@microsoft.com

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