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Network Working Group                                 G. Montenegro
Internet Draft                                            D. Thaler
Intended status: Informational                       Shyam Seshadri
                                              Microsoft Corporation
Expires: September 4, 2009                            March 4, 2009


                     Multiple Interfaces on Windows
                  draft-montenegro-mif-multihoming-00


Status of this Memo

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   This Internet-Draft will expire on September 4, 2009.




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Copyright

   Copyright (c) 2009 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
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-
   info). Please review these documents carefully, as they describe
   your rights and restrictions with respect to this document.



Abstract

   Increasingly, hosts have more than one network interface active
   at any given point in time. Such multiplicity of interfaces
   leads to multiple and potentially conflicting (or overlapping)
   sets of configuration information and policies. How these are
   arbitrated and managed influence how the host resolves DNS
   queries, and-with respect to outgoing packets-how it selects a
   source address and an outgoing interface.



Table of Contents


   1. Introduction...................................................2
      1.1. Requirements Language.....................................3
      1.2. Terminology...............................................3
   2. Default Router Selection.......................................3
   3. Selecting the Proper Interface for Outgoing or Incoming Packets4
   4. DNS Configuration..............................................4
      4.1. Host-wide DNS configuration...............................4
      4.2. Interface-specific DNS configuration......................5
   5. DNS Names and Dynamic DNS Behavior.............................5
   6. DNS Query Behavior.............................................5
   7. Security Considerations........................................6
   8. IANA Considerations............................................6
   9. Acknowledgments................................................6
   10. References....................................................6
      10.1. Normative References.....................................6
      10.2. Informative References...................................7

1. Introduction

   Increasingly, hosts have more than one network interface active
   at any given point in time. In such scenarios, it is important
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   to distinguish between host-wide and interface-specific
   networking configuration information and policies. In addition
   to these (hopefully) disjoint sets, such multiplicity of
   interfaces may lead to potentially conflicts or overlaps. The
   arbitration and management of these sets of policy or
   configuration influence how the host behaves: e.g., how it
   selects a source address and an outgoing interface with respect
   to outgoing packets, and how it resolves DNS queries.

   This document explains how the Microsoft Windows family of
   operating systems handles multi-homing for hosts. Furthermore,
   it only discusses host behavior, not router behavior. It is
   offered to aid discussion with respect to the MIF BoF [MIFPS],
   and is not guaranteed to be correct nor complete. More detailed
   and authoritative information on Microsoft Corporation's
   protocol implementations can be found in other sources such as
   MSDN (http://msdn.microsoft.com/en-us/default.aspx), the MCPP
   (http://www.microsoft.com/protocols/mcpp.mspx) or WSPP
   (http://www.microsoft.com/protocols/wspp/wspp.mspx) Protocol
   Documentation series.



1.1. Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described
   in RFC 2119 [RFC2119].

1.2. Terminology

   Preferred interface - This is the first interface bound to the
             TCP/IP stack during bootup, but this ordering can be
             changed programmatically or via user interface. The
             preferred interface has been used in previous versions
             of Windows for routing and is also used for DNS query
             purposes.



2. Default Router Selection

   It is possible to configure default routes for different interfaces,
   leading to more than one default router. This is not desirable, as it
   may lead to inconsistent results, given that interfaces may connect
   to disjoint networks. If there are multiple such default routes, the
   usual routing precedence decides which one is used. First, the
   interface with the lowest metric is preferred (generally, the faster
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   an interface, the lower its metric). If multiple interfaces share the
   same metric (e.g., because they have equal or very similar nominal
   speeds), then behavior changed starting with Windows Vista.
   Previously, the default route on the preferred interface is used.

   With Windows Vista, such preferred interface is not used for routing.
   Instead, host-to-router load sharing [RFC4311] is used for both IPv4
   and IPv6.

   For more information, refer to [DefGateway].

3. Selecting the Proper Interface for Outgoing or Incoming Packets

   For outgoing packets whose source address has not been determined
   previously by applications, the stack chooses from addresses assigned
   to its interfaces. Similarly, for incoming packets, valid destination
   addresses must match the address of one of its interfaces. Per host
   requirements [RFC1122], such choices depend on whether a host
   implements the strong or weak host model.

   Windows has implemented the weak host model on IPv4 as follows:
   Windows 2000, Windows XP and Windows Server 2003. IPv6 has always
   implemented the strong host model (starting with Windows XP and
   Windows Server 2003). Starting with Windows Vista and Windows Server
   2008, the strong host model became the default for IPv4 as well,
   although the weak model is still possible via per-interface
   configuration.

   For IPv6, Windows follows [RFC3484]. Starting in Vista, Windows
   follows 3484 for IPv4 as well.  Prior to Vista, IPv4 would choose the
   first address on the outgoing interface for all traffic where the
   application didn't specify a source address.

   For more information, see [StrongAndWeakHost] and [SrcDstSel].

4. DNS Configuration

   A Windows host has host-wide as well as interface-specific
   configuration items.

4.1. Host-wide DNS configuration

   Host-wide DNS configuration is input either via static configuration
   or via Microsoft's Group Policy. The latter, however, is available
   only within deployments that make use of Active Directory (e.g.,
   within corporate or enterprise environments). Upon joining an Active
   Directory domain, clients may receive such configuration.

   The host-wide DNS configuration comprises the following:
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   .  Primary DNS suffix - This is typically set to the domain name of
     the Active Directory in environments in which the host joins a
     domain. Otherwise, this can be set via static configuration. This
     can be set to something other than the Active Directory domain,
     and is sometimes unavoidable (e.g., upon corporate mergers), but
     is not recommended.

   .  Host-wide suffix list - Host-wide list of suffixes that can be
     appended to names being queried (see "DNS Query Behavior" below).
     Prior to Windows Vista, this would be appended to any unqualified
     multi-label query (e.g., to names not ending in a ".").  As of
     Vista, this is by default only appended to single-label queries
     (although the previous behavior is still configurable).

   Before Windows Vista and Windows Server 2008 there used to be a
   global DNS servers configuration which took precedence over the per-
   interface DNS servers (see below). This global value is now
   deprecated.

4.2. Interface-specific DNS configuration

   Interface-specific DNS configuration is input either via static
   configuration or via DHCP.

   .  Interface-specific suffix list

   .  List of DNS server IP addresses - The first one is the "primary"
     with all others being secondary.



5. DNS Names and Dynamic DNS Behavior

   TBD



6. DNS Query Behavior

   The DNS Client service queries the DNS servers in the following
   order:

   1. The DNS Client service sends the name query to the first DNS
     server on the preferred interface's list of DNS servers and waits
     one second for a response.

   2. If the DNS Client service does not receive a response from the
     first DNS server within one second, it sends the name query to the

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     first DNS servers on all interfaces that are still under
     consideration and waits two seconds for a response.

   3. If the DNS Client service does not receive a response from any DNS
     server within two seconds, the DNS Client service sends the query
     to all DNS servers on all interfaces that are still under
     consideration and waits another two seconds for a response.

   4. If the DNS Client service still does not receive a response from
     any DNS server, it sends the name query to all DNS servers on all
     interfaces that are still under consideration and waits four
     seconds for a response.

   5. If it the DNS Client service does not receive a response from any
     DNS server, the DNS client sends the query to all DNS servers on
     all interfaces that are still under consideration and waits eight
     seconds for a response.

   More information is available at sources such as [DNSWorks] (See, for
   example, "Overview of DNS Query Process" or [DNSClient].



7. Security Considerations

   TBD.

8. IANA Considerations

   This document has no IANA considerations.

9. Acknowledgments

   The authors would like to acknowledge the following people for
   their feedback and interesting discussions.



10. References

10.1. Normative References

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





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10.2. Informative References

   [DefGateway] Default Gateway Behavior for Windows TCP/IP:
             http://technet.microsoft.com/en-
             us/library/bb878104.aspx

   [DNSClient] Domain Name System Client Behavior in Windows Vista:
             http://technet.microsoft.com/en-
             us/library/bb727035.aspx

   [DNSWorks] How DNS Works: http://technet.microsoft.com/en-
             us/library/cc772774.aspx

   [MIFPS] Blanchet, M., "Multiple Interfaces Problem
             Statement",draft-blanchet-mif-problem-statement-00.txt
             (work in progress), December 2008.

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

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

   [RFC4191] R. Draves, D. Thaler, "Default Router Preferences and
             More-Specific Routes", RFC 4191, November 2005.

   [RFC4311] R. Hinden, D. Thaler, "IPv6 Host-to-Router Load
             Sharing", RFC 4311, November 2005.

   [SrcDstSel] Source and Destination Address Selection for IPv6:
             http://microsoft.com/technet/community/columns/cablegu
             y/cg0206.mspx

   [StrongAndWeakHost] Strong and Weak Host Models
             http://technet.microsoft.com/en-
             us/magazine/2007.09.cableguy.aspx













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Author's Addresses

   Gabriel Montenegro
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052
   USA

   Phone:
   Email: gabriel.montenegro@microsoft.com


   Dave Thaler
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052
   USA

   Phone:
   Email: dthaler@microsoft.com


   Shyam Seshadri
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052
   USA

   Phone:
   Email: sseshad@microsoft.com



















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