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Versions: (draft-blanchet-mif-problem-statement) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 6418

Network Working Group                                        M. Blanchet
Internet-Draft                                                  Viagenie
Intended status: Informational                                  P. Seite
Expires: September 12, 2011                      France Telecom - Orange
                                                          March 11, 2011

     Multiple Interfaces and Provisioning Domains Problem Statement


   This document describes issues encountered by a node attached to
   multiple provisioning domains.  This node receives configuration
   information from each of its provisioning domains where some
   configuration objects are global to the node, others are local to the
   interface.  Issues such as selecting the wrong interface to send
   trafic happen when conflicting node-scoped configuration objects are
   received and inappropriately used.  Moreover, other issues are the
   result of simulatenous attachment to multiple networks, such as
   domain selection or addressing and naming space overlaps, regardless
   of the provisioning mechanism.  While multiple provisioning domains
   are typically seen on nodes with multiple interfaces, this document
   also discusses single interface nodes situation.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 12, 2011.

Copyright Notice

   Copyright (c) 2011 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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   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Scope and Existing Work  . . . . . . . . . . . . . . . . . . .  4
     3.1.  Below IP Interaction . . . . . . . . . . . . . . . . . . .  4
     3.2.  MIF node Characterization  . . . . . . . . . . . . . . . .  4
     3.3.  Hosts Requirements . . . . . . . . . . . . . . . . . . . .  5
     3.4.  Mobility and other IP protocols  . . . . . . . . . . . . .  6
     3.5.  Address Selection  . . . . . . . . . . . . . . . . . . . .  6
     3.6.  Finding and Sharing IP Addresses with Peers  . . . . . . .  6
     3.7.  Interface and Provisioning domain selection  . . . . . . .  7
     3.8.  Session management . . . . . . . . . . . . . . . . . . . .  7
     3.9.  Socket API . . . . . . . . . . . . . . . . . . . . . . . .  8
   4.  MIF Issues . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  DNS resolution issues  . . . . . . . . . . . . . . . . . .  9
     4.2.  Node Routing . . . . . . . . . . . . . . . . . . . . . . . 10
     4.3.  Policies conflict  . . . . . . . . . . . . . . . . . . . . 11
     4.4.  Session management . . . . . . . . . . . . . . . . . . . . 12
     4.5.  Single Interface on Multiple Provisioning Domains  . . . . 12
   5.  Underlying problems and causes . . . . . . . . . . . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   8.  Authors  . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   10. Informative References . . . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19

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1.  Introduction

   A multihomed node may have multiple provisioning domains (via
   physical and/or virtual interfaces).  For example, a node may be
   simultaneously connected to a wired Ethernet LAN, a 802.11 LAN, a 3G
   cell network, one or multiple VPN connections or one or multiple
   tunnels(automatic or manual).  Current laptops and smartphones
   typically have multiple access network interfaces and, thus, are
   often connected to different provisioning domains.

   A multihomed node receives configuration information from each of its
   attached networks, through various mechanisms such as DHCPv4
   [RFC2131], DHCPv6 [RFC3315], PPP [RFC1661] and IPv6 Router
   Advertisements [RFC4861].  Some received configuration objects are
   specific to an interface such as the IP address and the link prefix.
   Others are typically considered by implementations as being global to
   the node, such as the routing information (e.g. default gateway), DNS
   servers IP addresses, and address selection policies, herein named

   When the received node-scoped configuration objects have different
   values from each provisioning domains, such as different DNS servers
   IP addresses, different default gateways or different address
   selection policies, the node has to decide which one to use or how it
   will merge them.

   Other issues are the result of simulatenous attachment to multiple
   networks, such as addressing and naming space overlaps, regardless of
   the provisioning mechanism.

   The following sections define the multiple interfaces (MIF) node, the
   scope of this work, describe related work, list issues and then
   summarize the underlying problems.

   A companion document [I-D.ietf-mif-current-practices] discusses some
   current practices of various implementations dealing with MIF.

2.  Terminology

   Administrative domain

      A group of hosts, routers, and networks operated and managed by a
      single organization [RFC1136].

   Provisioning domain

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      A set of consistent configuration information (e.g.  Default
      router, Network prefixes, DNS,...).  One administrative domain may
      have multiple provisioning domains.

   Reference to IP version

      When a protocol keyword such as IP, PPP, DHCP is used in this
      document without any reference to a specific IP version, then it
      implies both IPv4 and IPv6.  A specific IP version keyword such as
      DHCPv4 or DHCPv6 is meant to be specific to that IP version.

3.  Scope and Existing Work

   This section describes existing related work and defines the scope of
   the problem.

3.1.  Below IP Interaction

   Some types of interfaces have link layer characteristics which may be
   used in determining how multiple provisioning domain issues will be
   dealt with.  For instance, link layers may have authentication and
   encryption characteristics which could be used as criteria for
   interface selection.  However, network discovery and selection on
   lower layers as defined by [RFC5113] is out of scope of this
   document.  Moreover, interoperability with lower layer mechanisms
   such as services defined in IEEE 802.21, which aims at facilitating
   handover between heterogeneous networks [802.21], is also out of

   Some mechanisms (e.g., based on a logical IP interface)
   allow sharing a single IP address over multiple
   interfaces to networks with disparate access technologies.  From the
   IP stack view on the node, there is only a single interface and
   single IP address.  Therefore, this situation is out of scope of this
   current problem statement.  Furthermore, link aggregation done under
   IP where a single interface is shown to the IP stack is also out of

3.2.  MIF node Characterization

   A MIF node has the following characteristics:

   o  A [RFC1122] IPv4 and/or [RFC4294] IPv6 compliant node
   o  A MIF node is configured with more than one IP addresses
      (excluding loopback and link-local)

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   o  A MIF node can attach to more than one provisioning domains, as
      presented to the IP stack.
   o  The interfaces may be logical, virtual or physical.
   o  Configuration objects come from one or more administrative
   o  The IP addresses may be from the same or from different address
      families, such as IPv4 and IPv6.
   o  Communications using these IP addresses may happen simultaneously
      and independently.
   o  Some communications using these IP addresses are possible on all
      the provisioning domains, while some are only possible on a
      smaller set of the provisioning domains.
   o  While the MIF node may forward packets between its interfaces,
      forwarding packets is not taken into account in this definition
      and is out of scope for this document.

3.3.  Hosts Requirements

   The requirements for Internet Hosts [RFC1122] describe the multihomed
   node as if it has multiple IP addresses, which may be associated with
   one or more physical interfaces connected to the same or different

   The requirements states that The node maintains a route cache table
   where each entry contains the local IP address, the destination IP
   address, Type-of-Service and Next-hop gateway IP address.  The route
   cache entry would have data about the properties of the path, such as
   the average round-trip delay measured by a transport protocol.
   Nowadays, implementations are not caching these informations.

   [RFC1122] defines two host models:
   o  The "Strong" host model defines a multihomed host as a set of
      logical hosts within the same physical host.  In this model a
      packet must be sent on an interface that corresponds to the source
      address of that packet.
   o  The "Weak" host model describes a host that has some embedded
      gateway functionality.  In the weak host model, the host can send
      and receive packets on any interface.

   The multihomed node computes routes for outgoing datagrams
   differently depending on the model.  Under the strong model, the
   route is computed based on the source IP address, the destination IP
   address and the Type-of-Service.  Under the weak model, the source IP
   address is not used, but only the destination IP address and the

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3.4.  Mobility and other IP protocols

   The scope of this document is only about nodes implementing [RFC1122]
   for IPv4 and [RFC4294] for IPv6 without additional features or
   special-purpose support for transport layers, mobility, multi-homing,
   or identifier-locator split mechanisms.  Dealing with multiple
   interfaces with such mechanisms is related but considered as a
   separate problem and is under active study elsewhere in the IETF
   [RFC4960], [RFC5206], [RFC5533], [RFC5648],

   When an application is using one interface while another interface
   with better characteristics becomes available, the ongoing
   application session could be transferred to the newly enabled
   interface.  However, in some cases, the ongoing session shall be kept
   on the current interface while initiating the new sessions on the new
   interface.  The problem of the interface selection is within the MIF
   scope and may leverage specific node functions (Section 3.8).
   However, if transfer of IP session is required, IP mobility
   mechanisms, such as [RFC3775], shall be used.

3.5.  Address Selection

   The Default Address Selection specification [RFC3484] defines
   algorithms for source and destination IP address selections.  It is
   mandatory to be implemented in IPv6 nodes, which also means dual-
   stack nodes.  A node-scoped policy table managed by the IP stack is
   defined.  Mechanisms to update the policy table are being defined
   [I-D.ietf-6man-addr-select-sol] to update the policy table.

   Issues on using the Default Address Selection were found in [RFC5220]
   and [RFC5221] in the context of multiple prefixes on the same link.

3.6.  Finding and Sharing IP Addresses with Peers

   Interactive Connectivity Establishment (ICE [RFC5245]) is a technique
   for NAT traversal for UDP-based (and TCP) media streams established
   by the offer/answer model.  The multiplicity of IP addresses, ports
   and transport in SDP offers are tested for connectivity by peer-to-
   peer connectivity checks.  The result is candidate IP addresses and
   ports for establishing a connection with the other peer.  However,
   ICE does not solve issues when incompatible configuration objects are
   received on different interfaces.

   Some application protocols do referrals of IP addresses, port numbers
   and transport for further exchanges.  For instance, applications can
   provide reachability information to itself or to a third party.  The
   general problem of referrals is related to the multiple interface

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   problem, since, in this context, referrals must provide consistent
   information depending on which provisioning domain is used.
   Referrals are discussed in [I-D.carpenter-behave-referral-object] and

3.7.  Interface and Provisioning domain selection

   In a MIF context, the node may handle simultaneously multiple domains
   with disparate characteristics, especially when supporting multiple
   access technologies.  Selection is simple if the application is
   restricted to one specific provisioning domain: the application must
   start on the default provisioning domain if available, otherwise the
   application does not start.  However, if the application can be run
   on several provisioning domains, the selection problem can be

   For example, the interface selection mechanism defined in [TS23.234]
   uses the following information (non exhaustive list):

   o  preferences provided by the user,
   o  policies provided by network operator,
   o  quality of the radio link,
   o  network resource considerations (e.g. available QoS, IP
      connectivity check,...),
   o  the application QoS requirements in order to map applications to
      the best interface

   However, [TS23.234] is designed for a specific multiple-interfaces
   use-case.  A generic way to handle these characteristics is yet to be

3.8.  Session management

   Some implementations, specially in the mobile world, rely on higher-
   level session manager, also named connection manager, to deal with
   issues brought by simultaneous attachment to multiple provisioning
   domains.  Typically, the connection manager may deal with the
   selection of the interface, and/or the provisioning domain, on behalf
   to the applications, or tackle with complex issues such as policies
   conflict resolution (Section 4.3).  As discussed previously in
   Section 3.7, the connection manager may encounter difficulties
   because of multiple and diverse criteria.

   Connection managers usually leverage the link-layer interface to
   gather information (e.g lower layer authentication and encryption
   methods, see Section 3.1) and/or for control purpose.  Such link-
   layer interface may not provide all required services to make a
   proper decision (e.g. interface selection).  Some OS, or terminals,

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   already implement connection managers
   [I-D.ietf-mif-current-practices] and vendor-specific platforms
   sometimes provides specific socket API (Section 3.9) a connection
   manager can use.  However, the generic architecture of a connection
   manager and its associated API are not currently standardized, so
   session management behavior may differ between OS and platforms.

   Multiple interfaces management sometimes relies on a logical
   interface.  For instance, logical interface allows to support multi-
   homing, inter-technology handovers and IP flow mobility in a Proxy
   Mobile IPv6 network [I-D.ietf-netext-logical-interface-support].
   This virtual interface allows a multiple-interfaces node sharing a
   set of IP addresses on multiple physical interfaces and can also add
   benefits to multi-access scenarios such as 3GPP Multi Access PDN
   Connectivity [TS23.402].  In most cases, the virtual interface will
   map several physical network interfaces and the connection manager
   should control both, the configuration of each one of these virtual
   and physical interfaces, as well as the mapping between the virtual
   and the sub-interfaces.

   In multiple interfaces situation, active application sessions should
   survive to path failures.  Here, the connection manager may come into
   play but only relying on existing mechanisms to manage multipath
   (MPTCP [I-D.ietf-mptcp-architecture]) or failover (MIP6 [RFC3775],
   SHIM6 [RFC5533]).  Description of interaction between these
   mechanisms and the connection manager is out of the scope of this

3.9.  Socket API

   An Application Programming Interface (API) may expose objects that
   user applications, or connection managers, use for dealing with
   multiple interfaces.  For example, [RFC3542] defines how an
   application using the Advanced sockets API specifies the interface or
   the source IP address, through a simple bind() operation or with the
   IPV6_PKTINFO socket option.

   Other APIs have been defined to solve similar issues to MIF.  For
   instance, [RFC5014] defines an API to influence the default address
   selection mechanism by specifying attributes of the source addresses
   it prefers.  [I-D.ietf-shim6-multihome-shim-api] gives another
   example, in a multihoming context, by defining a socket API enabling
   interactions between applications and the multihoming shim layer for
   advanced locator management, and access to information about failure
   detection and path exploration.

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4.  MIF Issues

   This section describes the various issues when using a MIF node that
   has already received configuration objects from its various
   provisioning domains or when multiple interfaces are used and results
   in wrong domain selection, addressing or naming space overlaps.  They
   occur, for example, when:

   1.  one interface is on the Internet and one is on a corporate
       private network.  The latter may be through VPN.
   2.  one interface is on one access network (i.e. wifi) and the other
       one is on another access network (3G) with specific services.

4.1.  DNS resolution issues

   A MIF node (M1) has an active interface(I1) connected to a network
   (N1) which has its DNS server (S1) and another active interface (I2)
   connected to a network (N2) which has its DNS server (S2).  S1 serves
   with some private namespace "private.example.com".  The user or the
   application uses a name "a.private.example.com" which is within the
   private namespace of S1 and only resolvable by S1.  Any of the
   following situations may occur:

   1.  M1 stack, based on its routing table, uses I2 to reach S1 to
       resolve "a.private.example.com".  M1 never reaches S1.  The name
       is not resolved.
   2.  M1 keeps only one set of DNS server addresses from the received
       configuration objects and kept S2 address.  M1 sends the forward
       DNS query for a.private.example.com to S2.  S2 responds with an
       error for an non-existent domain (NXDOMAIN).  The name is not
       resolved.  This issue also arises when performing reverse DNS
       lookup.  In the same situation, the reverse DNS query fails.
   3.  M1 keeps only one set of DNS server addresses from the received
       configuration objects and kept S2 address.  M1 sends the DNS
       query for a.private.example.com to S2.  S2 asks its upstream DNS
       and gets an IP address for a.private.example.com.  However, the
       IP address is not the same one S1 would have given.  Therefore,
       the application tries to connect to the wrong destination node,
       or to the wrong interface of the latter, which may imply security
       issues or result in lack of service.
   4.  S1 or S2 has been used to resolve "a.private.example.com" to an
       [RFC1918] address.  Both N1 and N2 are [RFC1918] addressed
       networks.  Traffic may be sent using the wrong interface.  This
       issue is not related to receiving multiple configuration objects,
       but to an address overlap between interfaces or attaching

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   5.  M1 has resolved an FQDN to locally valid IP address when
       connected to N1.  If the node looses connection to N1, the node
       may try to connect, via N2, to the same IP address as earlier,
       but as the address was only locally valid, connection setup
       fails.  Similarly, M1 may have received NXDOMAIN for an FQDN when
       connected to N1.  After detachment from N1, the node should not
       assume the FQDN continues to be nonexistent on N2.
   6.  M1 requests AAAA record from a DNS server on a network that uses
       protocol translators and DNS64 [I-D.ietf-behave-dns64].  If the
       M1 receives synthesized AAAA record, it is guaranteed to be valid
       only on the network it was learned from.  If the M1 uses
       synthesized AAAA on any other network interface, traffic may be
       lost, dropped or forwarded to the wrong network.

4.2.  Node Routing

   A MIF node (M1) has an active interface(I1) connected to a network
   (N1) and another active interface (I2) connected to a network (N2).
   The user or the application is trying to reach an IP address (IP1).
   Any of the following situations may occur:

   1.  For IP1, M1 has one default route (R1) via network (N1).  To
       reach IP1, M1 stack uses R1 and sends through I1.  If IP1 is only
       reachable by N2, IP1 is never reached or is not the right target.
   2.  For the IP1 address family, M1 has one default route (R1, R2) per
       network (N1, N2).  IP1 is reachable by both networks, but N2 path
       has better characteristics, such as better round-trip time, least
       cost, better bandwidth, etc....  These preferences could be
       defined by user, provisioned by the network operator, or else.
       M1 stack uses R1 and tries to send through I1.  IP1 is reached
       but the service would be better by I2.
   3.  For the IP1 address family, M1 has a default route (R1), a
       specific X.0.0.0/8 route R1B (for example but not restricted to
       RFC1918 prefix) to N1 and a default route (R2) to N2.  IP1 is
       reachable by N2 only, but the prefix (X.0.0.0/8) is used in both
       networks.  Because of the most specific route R1B, M1 stack sends
       through I2 and never reach the target.

   A MIF node may have multiple routes to a destination.  However, by
   default, it does not have any hint concerning which interface would
   be the best to use for that destination.  The first-hop selection may
   leverage on local routing policy, allowing some actors (e.g. network
   operator or service provider) to influence the routing table, i.e.
   make decision regarding which interface to use.  For instance, a user
   on such multihomed node might want a local policy to influence which
   interface will be used based on various conditions.  Some SDOs have
   defined policy-based routing selection mechanisms.  For instance, the
   Access Network Discovery and Selection Function (ANDSF) [TS23.402]

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   provides inter-systems routing policies to terminals with both a 3GPP
   and non-3GPP interfaces.  However, the routing selection may still be
   difficult, due to disjoint criteria as discussed in Section 3.8.
   Moreover, information required to make the right decision may not be
   available.  For instance, interfaces to lower layer may not provide
   all required hints to the selection (e.g. information on interface

   A node usually has a node-scoped routing table.  A MIF node is
   connected to multiple provisioning domains.  If each of these domains
   pushes routing policies to the node, then conflicts between policies
   may happen and the node has no easy way to merge or reconciliate

   On a MIF node, some source addresses are not valid if used on some
   interfaces.  For example, an RFC1918 source address might be
   appropriate on the VPN interface but not on the public interface of
   the MIF node.  If the source address is not chosen appropriately,
   then packets may be filtered in the path if source address filtering
   is in place ([RFC2827], [RFC3704]) and reply packets may never come
   back to the source.

4.3.  Policies conflict

   The distribution of configuration policies (e.g. address selection,
   routing, DNS selection...) to end nodes is being discussed (e.g.
   ANDSF in [TS23.402], [I-D.ietf-mif-dhcpv6-route-option]).  If
   implemented in multiple provisioning domains, such mechanisms may
   conflict and bring issues to the multihomed node.  Considering a MIF
   node (M1) with an active interface(I1) connected to a network (N1)
   and another active interface (I2) connected to a network (N2), the
   following conflicts may occur:
   1.  M1 receives from both networks (N1 and N2) an update of its
       default address selection policy.  However, the policies are
       specific to each network.  The policies are merged by M1 stack.
       Based on the merged policy, the chosen source address is from N1
       but packets are sent to N2.  The source address is not reachable
       from N2, therefore the return packet is lost.  Merging address
       selection policies may have important impacts on routing.
   2.  A node usually has a node-scoped routing table.  However, each of
       the connected provisioning domains (N1 and N2) may push routing
       policies to the node, then conflicts between policies may happen
       and the node has no easy way to merge or reconciliate them.
   3.  M1 receives from one of the network an update of its access
       selection policy, e.g. via the 3GPP/ANDSF [TS23.402].  However,
       the policy is in conflict with the local policy (e.g. user
       defined, or default OS policy).  Assuming that the network
       provides list of overloaded access network, if the policy sent by

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       the network is ignored, packet may be sent to an access network
       with poor quality of communication.

4.4.  Session management

   Consider that a node has selected an interface and managed to
   configure it (i.e. the node obtained a valid IP address from the
   network).  However, the Internet connectivity is not available.  The
   problem could be due to the following reasons:
   1.  The network requires a web-based authentication (e.g. the access
       network is a WiFi Hot Spot).
   2.  IP interface is configured active but layer 2 is so poor (e.g.
       poor radio condition) that no layer 3 traffic can succeed.

   In this situation, the session management should be able to perform
   IP connectivity checks before selecting an interface.

   Session issues may also arise when the node discovers a new
   provisioning domain.  Consider a MIF node (M1) has an active
   interface(I1) connected to a network (N1) where an application is
   running a TCP session.  A new network (N2) becomes available.  If N2
   is selected (e.g. because of better quality of communication), M1
   gets IP connectivity to N2 and updates the routing table priority.
   So, if no specific route to the correspondent node and if the node
   implements the weak host model [RFC1122], the TCP connection breaks
   as next hop changes.  In order to continue communicating with the
   correspondent node, M1 should try to re-connect the server via N2.
   In some situation, it could be preferable to maintain current
   sessions on N1 while new sessions start on N2.

4.5.  Single Interface on Multiple Provisioning Domains

   When a node using a single interface is connected to multiple
   networks, such as different default routers, similar issues as
   described above happen.  Even with a single interface, a node may
   wish to connect to more than one provisioning domain: that node may
   use more than one IP source address and may have more than one
   default router.  The node may want to access services that can only
   be reached using one of the provisioning domain.  In this case, it
   needs to use the right outgoing source address and default gateway to
   reach that service.  In this situation, that node may also need to
   use different DNS servers to get domain names in those different
   provisioning domains.

5.  Underlying problems and causes

   This section lists the underlying problems, and their causes, which

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   lead to the issues discussed in the previous section.  The problems
   can be divided into five categories: 1) Configuration 2) DNS
   resolution 3) Routing 4) Address selection and 5) connection
   management and API.  They are shown as below:

   1.  Configuration.  In a MIF context, configuration information
       specific to a provisioning domain may be ignored because:
       1.  Configuration objects (e.g.  DNS servers, NTP servers, ...)
           are node-scoped.  So the IP stack is not able to maintain the
           mapping between information and corresponding provisioning
       2.  Same configuration objects (e.g.  DNS server addresses, NTP
           server addresses, ..) received from multiple provisioning
           domains may be overwritten.
       3.  Host implementations usually do not keep separate network
           configuration (such as DNS server addresses) per provisioning
   2.  DNS resolution
       1.  Some FQDN can be resolvable only by sending queries to the
           right server (e.g. intranet services).  However, DNS query
           could be sent to the wrong interface because DNS server
           addresses may be node-scoped.
       2.  A DNS answer may be only valid on a specific provisioning
           domain but applications may not be aware of that mapping
           because DNS answers may not be kept with the provisioning
           from which the answer comes from.
   3.  Routing
       1.  In the MIF context, routing information could be specific to
           each interface.  This could lead to routing issue because, in
           current node implementations, routing tables are node-scoped.
       2.  Current node implementations do not take into account the
           Type-of-Service or path characteristics in the routing table.
       3.  Even if implementations take into account path
           characteristics, the node has no way to properly merge or
           reconciliate the provisioning domain preferences.
       4.  a node attached to multiple provisioning domain could be
           provided with incompatible selection policies.  If the
           different actors (e.g. user and network operator) are allowed
           to provide their own policies, the node has no way to
           properly merge or reconciliate multiple selection policies.
       5.  The problem of first hop selection could not be solved via
           configuration (Section 3.7), and may leverage on
           sophisticated and specific mechanisms (Section 3.8).
   4.  Address selection
       1.  Default Address Selection policies may be specific to their
           corresponding provisioning domain.  However, a MIF node may
           not be able to manage per-provisioning domain address
           selection policies because default Address Selection policy

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           is node-scoped.
       2.  On a MIF node, some source addresses are not valid if used on
           some interfaces or even on some default routers on the same
           interface.  In this situation, the source address should be
           taken into account in the routing table; but current node
           implementations do not support such a feature.
       3.  Source address or address selection policies could be
           specified by applications.  However, there is no advanced
           APIs to allow applications realizing such operations.
   5.  Session management and API
       1.  Some implementations, specially in the mobile world, have
           higher-level API and/or connection manager to address MIF
           issues.  These mechanisms are not standardized and do not
           necessarily behave the same way across different OS, and/or
           platforms, in the presence of the MIF problems.  This lack of
           consistency is an issue for user and operator who could
           experience different connection manager behaviors depending
           on the terminal.
       2.  Connection managers usually leverage on interface to link
           layer to gather information (e.g lower layer authentication
           and encryption methods) and/or for control purpose.  However,
           such link layer interface may not provide all required
           services (e.g. may not provide all information allowing to
           make a proper interface selection).
       3.  A MIF node can support different connection managers, which
           may have contradictory ways to solve the MIF issues.  For
           instance, because of different selection algorithms, two
           different connection managers could select different domains
           in a same context.  Or, when dealing with different domain
           selection policies, a connection manager may give precedence
           to user policy while another could favor mobile operator
       4.  When host routing is updated and if weak host model is
           supported, ongoing TCP sessions may break if routes changes
           for these sessions.  When TCP sessions should be bound to the
           interface, the strong host model should be used.
       5.  When provided by different actors (e.g. user, network,
           default-OS), policies may conflict and, thus, need to be
           reconciliated at the host level.  Policy conflict resolution
           may impact other functions (e.g. naming, routing).
       6.  Even if the node has managed to configure an interface,
           Internet connectivity could be not available.  It could be
           due to an access control function coming into play above the
           layer 3, or because of poor layer 2 conditions.  IP
           connectivity check should be performed before selecting an

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6.  Security Considerations

   The problems discussed in this document have security implications,
   such as when the packets sent on the wrong interface might be leaking
   some confidential information.  Configuration parameters from one
   provisioning domain could cause a denial of service on another
   provisioning domain (e.g.  DNS issues).  Moreover, the undetermined
   behavior of IP stacks in the multihomed context bring additional
   threats where an interface on a multihomed node might be used to
   conduct attacks targeted to the networks connected by the other
   interfaces.corrupted provisioning domain selection policy may induce
   a node to make decisions causing certain traffic to be forwarded to
   the attacker.

   Additional security concerns are raised by possible future mechanisms
   that provide additional information to the node so that it can make a
   more intelligent decision with regards to the issues discussed in
   this document.  Such future mechanisms may themselves be vulnerable
   and may not be easy to protect in the general case.

7.  IANA Considerations

   This document has no actions for IANA.

8.  Authors

   This document is a joint effort with authors of the MIF requirements
   draft [I-D.yang-mif-req].  The authors of this document, in
   alphabetical order, include: Marc Blanchet, Jacqni Qin, Pierrick
   Seite, Carl Williams and Peny Yang.

9.  Acknowledgements

   The initial Internet-Drafts prior to the MIF working group and the
   discussions during the MIF BOF meeting and on the mailing list around
   the MIF charter scope on the mailing list brought very good input to
   the problem statement.  This draft steals a lot of text from these
   discussions and initial drafts (e.g.  [I-D.yang-mif-req],
   [I-D.ietf-mif-dns-server-selection]).  Therefore, the editor would
   like to acknowledge the following people (in no specific order), from
   which some text has been taken from: Jari Arkko, Keith Moore, Sam
   Hartman, George Tsirtsis, Scott Brim, Ted Lemon, Bernie Volz, Giyeong
   Son, Gabriel Montenegro, Julien Laganier, Teemu Savolainen, Christian
   Vogt, Lars Eggert, Margaret Wasserman, Hui Deng, Ralph Droms, Ted

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   Hardie, Christian Huitema, Remi Denis-Courmont, Alexandru Petrescu,
   Zhen Cao, Gaetan Feige, Telemaco Melia and Juan-Carlos Zuniga.  Sorry
   if some contributors have not been named.

10.  Informative References

   [802.21]   IEEE, "IEEE Standard for Local and Metropolitan Area
              Networks - Part 21: Media Independent Handover Services,
              IEEE LAN/MAN Std 802.21-2008, January 2009.", 2010.

              Carpenter, B., Boucadair, M., Halpern, J., Jiang, S., and
              K. Moore, "A Generic Referral Object for Internet
              Entities", draft-carpenter-behave-referral-object-01 (work
              in progress), October 2009.

              Hui, M. and H. Deng, "Problem Statement and Requirement of
              Simple IP Multi-homing of the Host",
              draft-hui-ip-multiple-connections-ps-02 (work in
              progress), March 2009.

              Matsumoto, A., Fujisaki, T., and R. Hiromi, "Solution
              approaches for address-selection problems",
              draft-ietf-6man-addr-select-sol-03 (work in progress),
              March 2010.

              Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum,
              "DNS64: DNS extensions for Network Address Translation
              from IPv6 Clients to IPv4 Servers",
              draft-ietf-behave-dns64-11 (work in progress),
              October 2010.

              Wasserman, M. and P. Seite, "Current Practices for
              Multiple Interface Hosts",
              draft-ietf-mif-current-practices-08 (work in progress),
              February 2011.

              Dec, W., Mrugalski, T., Sun, T., and B. Sarikaya, "DHCPv6
              Route Option", draft-ietf-mif-dhcpv6-route-option-00 (work
              in progress), January 2011.


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              Savolainen, T. and J. Kato, "Improved DNS Server Selection
              for Multi-Homed Nodes",
              draft-ietf-mif-dns-server-selection-01 (work in progress),
              March 2011.

              Ford, A., Raiciu, C., Handley, M., Barre, S., and J.
              Iyengar, "Architectural Guidelines for Multipath TCP
              Development", draft-ietf-mptcp-architecture-05 (work in
              progress), January 2011.

              Melia, T. and S. Gundavelli, "Logical Interface Support
              for multi-mode IP Hosts",
              draft-ietf-netext-logical-interface-support-01 (work in
              progress), October 2010.

              Nordmark, E., "Shim6 Application Referral Issues",
              draft-ietf-shim6-app-refer-00 (work in progress),
              July 2005.

              Komu, M., Bagnulo, M., Slavov, K., and S. Sugimoto,
              "Socket Application Program Interface (API) for
              Multihoming Shim", draft-ietf-shim6-multihome-shim-api-16
              (work in progress), February 2011.

              Yang, P., Seite, P., Williams, C., and J. Qin,
              "Requirements on multiple Interface (MIF) of simple IP",
              draft-yang-mif-req-00 (work in progress), March 2009.

   [RFC1122]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.

   [RFC1136]  Hares, S. and D. Katz, "Administrative Domains and Routing
              Domains: A model for routing in the Internet", RFC 1136,
              December 1989.

   [RFC1661]  Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
              RFC 1661, July 1994.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",

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              RFC 2131, March 1997.

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, May 2000.

   [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.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

   [RFC3542]  Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei,
              "Advanced Sockets Application Program Interface (API) for
              IPv6", RFC 3542, May 2003.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, March 2004.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC4294]  Loughney, J., "IPv6 Node Requirements", RFC 4294,
              April 2006.

   [RFC4477]  Chown, T., Venaas, S., and C. Strauf, "Dynamic Host
              Configuration Protocol (DHCP): IPv4 and IPv6 Dual-Stack
              Issues", RFC 4477, May 2006.

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

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

   [RFC5014]  Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6
              Socket API for Source Address Selection", RFC 5014,
              September 2007.

   [RFC5113]  Arkko, J., Aboba, B., Korhonen, J., and F. Bari, "Network
              Discovery and Selection Problem", RFC 5113, January 2008.

   [RFC5206]  Nikander, P., Henderson, T., Vogt, C., and J. Arkko, "End-
              Host Mobility and Multihoming with the Host Identity
              Protocol", RFC 5206, April 2008.

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   [RFC5220]  Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
              "Problem Statement for Default Address Selection in Multi-
              Prefix Environments: Operational Issues of RFC 3484
              Default Rules", RFC 5220, July 2008.

   [RFC5221]  Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
              "Requirements for Address Selection Mechanisms", RFC 5221,
              July 2008.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              April 2010.

   [RFC5533]  Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
              Shim Protocol for IPv6", RFC 5533, June 2009.

   [RFC5648]  Wakikawa, R., Devarapalli, V., Tsirtsis, G., Ernst, T.,
              and K. Nagami, "Multiple Care-of Addresses Registration",
              RFC 5648, October 2009.

              3GPP, "3GPP system to Wireless Local Area Network (WLAN)
              interworking; TS 23.234", 2009.

              3GPP, "Architecture enhancements for non- 3GPP accesses;
              TS 23.402", 2010.

Authors' Addresses

   Marc Blanchet
   2875 boul. Laurier, suite D2-630
   Quebec, QC  G1V 2M2

   Email: Marc.Blanchet@viagenie.ca
   URI:   http://viagenie.ca

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   Pierrick Seite
   France Telecom - Orange
   4, rue du Clos Courtel, BP 91226
   Cesson-Sevigne  35512

   Email: pierrick.seite@orange-ftgroup.com

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