\
none yet                                                      A. Suhonen
Internet-Draft                         Tampere University of Technology,
Updates: 3484 (if approved)                                      Finland
Intended status: Experimental                              July 29, 2009
Expires: January 30, 2010


     Address Selection Using Source Address Specific Routing Tables
                         draft-axu-addr-sel-00

Status of this Memo

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   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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

   RFC 3484 defines two algorithms for default source and destination
   address selection, but it has several shortcomings as specified in
   RFC 5220.  RFC 5221 lists some requirements for any attempts to
   update the original RFC.  This document specifies an alternate
   address selection algorithm to fulfill those requirements.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
   2.  Filter Algorithm . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Link Local Scope . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Autoconfiguration for Global Scope . . . . . . . . . . . .  5
     2.3.  Site Local Scope . . . . . . . . . . . . . . . . . . . . .  5
     2.4.  Additional Filter Constraints  . . . . . . . . . . . . . .  6
     2.5.  Forwarding . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.6.  Dynamic Routing Protocols  . . . . . . . . . . . . . . . .  6
   3.  Precedences and Labels . . . . . . . . . . . . . . . . . . . .  7
     3.1.  Route and Table Preferences  . . . . . . . . . . . . . . .  7
       3.1.1.  Local and Link Local Scope Routing Tables  . . . . . .  8
       3.1.2.  Global Scope Routing Tables  . . . . . . . . . . . . .  8
       3.1.3.  Transition Technique Routing Tables  . . . . . . . . .  8
       3.1.4.  IPv4 Compatible Routing Tables . . . . . . . . . . . .  9
       3.1.5.  Reachability Information . . . . . . . . . . . . . . .  9
   4.  RFC3484 Rule Comparison  . . . . . . . . . . . . . . . . . . .  9
   5.  RFC5220 Concerns . . . . . . . . . . . . . . . . . . . . . . .  9
     5.1.  Multiple Routers on a Single Interface . . . . . . . . . .  9
     5.2.  Ingress Filtering Problem  . . . . . . . . . . . . . . . .  9
     5.3.  Half-Closed Network Problem  . . . . . . . . . . . . . . .  9
     5.4.  Combined Use of Global and ULA . . . . . . . . . . . . . . 10
     5.5.  Site Renumbering . . . . . . . . . . . . . . . . . . . . . 10
     5.6.  Multicast Source Address Selection . . . . . . . . . . . . 10
     5.7.  Temporary Address Selection  . . . . . . . . . . . . . . . 10
     5.8.  IPv4 or IPv6 Prioritization  . . . . . . . . . . . . . . . 11
     5.9.  ULA and IPv4 Dual-Stack Environment  . . . . . . . . . . . 11
     5.10. ULA or Global Prioritization . . . . . . . . . . . . . . . 11
   6.  RFC5221 Requirements . . . . . . . . . . . . . . . . . . . . . 11
     6.1.  Effectiveness  . . . . . . . . . . . . . . . . . . . . . . 11
     6.2.  Timing . . . . . . . . . . . . . . . . . . . . . . . . . . 11



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     6.3.  Dynamic Behavior Update  . . . . . . . . . . . . . . . . . 11
     6.4.  Node-Specific Behavior . . . . . . . . . . . . . . . . . . 12
     6.5.  Application-Specific Behavior  . . . . . . . . . . . . . . 12
     6.6.  Multiple Interface . . . . . . . . . . . . . . . . . . . . 12
     6.7.  Central Control  . . . . . . . . . . . . . . . . . . . . . 12
     6.8.  Next-Hop Selection . . . . . . . . . . . . . . . . . . . . 12
     6.9.  Compatibility with RFC 3493  . . . . . . . . . . . . . . . 12
     6.10. Compatibility and Interoperability with RFC 3484 . . . . . 13
     6.11. Security . . . . . . . . . . . . . . . . . . . . . . . . . 13
   7.  Implementation Issues and Other Concerns . . . . . . . . . . . 13
     7.1.  Low Memory and Power Concerns  . . . . . . . . . . . . . . 13
     7.2.  Differing Larger Scopes  . . . . . . . . . . . . . . . . . 13
     7.3.  Connection Pooling . . . . . . . . . . . . . . . . . . . . 14
     7.4.  Using Just One Table with Tags . . . . . . . . . . . . . . 14
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 15
     10.1. RFC5220 Considerations . . . . . . . . . . . . . . . . . . 15
     10.2. RFC5221 Requirements . . . . . . . . . . . . . . . . . . . 15
       10.2.1. List of threats introduced by new
               address-selection mechanism  . . . . . . . . . . . . . 15
       10.2.2. List of recommendations in which security
               mechanism should be applied  . . . . . . . . . . . . . 15
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 15
     11.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Appendix A.  Routing Table Example . . . . . . . . . . . . . . . . 16
     A.1.  Before . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     A.2.  After Conversion . . . . . . . . . . . . . . . . . . . . . 17
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19





















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1.  Introduction

   [RFC3484] defines default address selection rules for IPv6 and IPv4.
   Several shortcomings in the original address selection rules have
   been identified in [RFC5220] and its sister document [RFC5221]
   specifies some requirements for any attempts to update the original
   address selection algorithm.

   A further concern comes from multipath protocols.  When SCTP
   [RFC2960], for example, finds that its active source destination
   address pair is no longer functional, it will need to start searching
   for a new one.

   The communicating hosts may both have a dozen addresses so it might
   take unacceptably long to iterate through all combinations before
   finding a functional pair.  On the other hand, many of the invalid
   combinations could be filtered out using this algorithm, making the
   process noticeably faster.

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].


2.  Filter Algorithm

   When a host has several addresses, they SHOULD each be associated
   with their own routing tables.  When selecting source and destination
   addresses, the first stage is to filter out combinations where the
   routing table attached with the source (local) address does not have
   a valid route for the destination (remote) address.  In other words,
   if a destination address can't be found from the routing table for a
   given source address the system MUST discard that destination address
   for that source address.

   If none of the possible destination addresses can be found in the
   routing table for a source address, then that source address MUST be
   discarded for those destination addresses.

   One side effect of this filter algorithm is that it doesn't need to
   know anything about scopes.  The routing tables associated with
   source address candidates will determine what destination addresses
   they are usable with.  This effect is demonstrated below and later in
   this document.





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2.1.  Link Local Scope

   The routing table associated with a link local address (e.g.
   169.254.123.45%le0) SHOULD only have one external unicast route, the
   link local network for that link (e.g. 169.254.0.0%le0 /16).  In
   addition, if the host supports multicast on this link, a route for
   the local scope multicast space SHOULD also appear in this table.

   This means that the link local address is usable only with other link
   local addresses on the same link.

   The localhost addresses and prefixes (127.0.0.1/8 and ::1/128) SHOULD
   be treated like link local scope in this algorithm.

2.2.  Autoconfiguration for Global Scope

   When addresses are assigned to interfaces dynamically through
   stateless or stateful autoconfiguration the process usually also
   yields a default route.  That default route SHOULD be placed only
   into the routing table associated with that address.  In addition, if
   the host and network support multicast, a route for the global scope
   multicast space SHOULD also appear in this table.

   This usually means that the next hop of that default route will only
   be useable with the source address learned from that default router.

   Some autoconfiguration methods (see [RFC3442] and [RFC4191]) can be
   used to communicate other routes in addition to the default route.
   Those routes SHOULD likewise be added only into the routing table
   associated with the address configured using that same interchange.

   Examples of autoconfiguration methods include RARP, DHCPv4, ICMPv6
   RA, DHCPv6, Teredo, 6to4, ISATAP, PPP, mDNS.

2.3.  Site Local Scope

   The routing tables for site local addresses SHOULD have routes for
   site local address space.  They SHOULD NOT have the default route, so
   that they would be automatically eliminated when selecting address
   pairs for site external communication.

   However, if the site edge automatically translates site local
   addresses to global addresses, the routing tables associated with
   site local scope addresses MAY have the default route.







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2.4.  Additional Filter Constraints

   The address selection algorithm MAY also be given additional filter
   constraints, such as "use only link#3" or "do not use next-hop
   10.0.0.1".  [RFC5014] specifies an interface that does something very
   similar.

   Work is going on in the MIF-wg [I-D.blanchet-mif-problem-statement]
   to tie address selection and next-hop selection with DNS resolver
   selection and other similar resources.  That is, when using the DNS
   resolvers received from one DHCP server, the terminal should also
   always use the default route received from that DHCP server.

   This algorithm supports those efforts by making it possible to
   restrict a process to one routing table for both address resolution
   and selection.

2.5.  Forwarding

   If a host is configured to forward packets between networks, it
   SHOULD combine the routing tables for the networks in question into
   one.  Link local scope tables MUST NOT be combined.

   If the host has multiple addresses from different global scope
   prefixes then system administration MAY specify which addresses are
   combined to form routing tables.  The resulting functionality
   resembles the VRF functionality found in some modern routers.

   One purpose behind this algorithm is to move source routing burden
   from the network to the host.  So if a router wants to advertise two
   (or more) prefixes on the subnet, but to keep their routing separate,
   it should use different link local and link layer addresses when
   advertising them.  It can then choose the correct VRF to forward a
   packet depending on which link layer address it received it on.

2.6.  Dynamic Routing Protocols

   Hosts don't usually run dynamic routing protocols, but since they
   sometimes do, this subsection is included for completeness.

   Dynamic routing protocol instances are usually bound to links or
   interfaces.  With this algorithm network administrators MAY bind
   routing protocol instances to specific addresses or prefixes on a
   link and the routing tables associated with them.  The routing
   protocol instance MUST update only the routing table it is associated
   with.

   A reasonable default setting is that all addresses that are not link



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   local are associated with the routing protocol instance.  Thus, they
   will share a routing table.

   If the network administration wants to separate traffic belonging to
   different upstream operator prefixes, it may wish to run separate
   routing protocol instances throughout the network for different
   upstream prefixes.


3.  Precedences and Labels

   TBD

   My original thought was to follow the metrics systems of the original
   RFC here, since candidate filtering and proper next hop selection
   were my primary concerns.  However, it might be a good idea to just
   rethink the issue one more time.

   Perhaps it might be a good idea to associate preferences with
   individual routes and/or whole routing tables.  In that case, the
   routing table lookup performed in the filtering phase would also
   yield the precedence of the address in addition to next-hop
   information.

   The label abstraction used by the original RFC loosely corresponds to
   the routing table abstraction in this algorithm.  That is, different
   scopes had different labels in [RFC3484] but in this algorithm
   different scopes SHOULD have their own routing tables.

   The rest of this section outlines one approach to sorting addresses
   by preference.

3.1.  Route and Table Preferences

   Each routing table has a default precedence, meaning all routes added
   to that table will have that precedence in the absence of a specific
   precedence.

   This precedence MUST be used to sort the source and destination
   address pairs according to preference.  In effect, the precedence is
   for the address pair, not for a single address.

   When two routes have the same precedence, their prefix lengths MUST
   be compared and the longer prefix MUST be considered more preferable.

   The algorithm normally performs both source and destination address
   selection simultaneously and efficiently.




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   In order to perform source address selection, only one destination
   address SHOULD be presented to the algorithm, which will then look
   for the address in all tables and sort the source addresses where it
   was found according to the precedences.

   In order to perform destination address selection, only one source
   address SHOULD be presented to the algorithm along with the set of
   destination addresses.  The algorithm will then look for all the
   given destination addresses in the table associated with the source
   address and sort the results according to the precedences.

3.1.1.  Local and Link Local Scope Routing Tables

   The default precedence for all local and link local scope route
   entries SHOULD be 50.

3.1.2.  Global Scope Routing Tables

   The default precedence for all global scope route entries SHOULD be
   40.

   System or network administrators or operating systems MAY alter this
   default precedence to account for things like link speeds.  Such
   environmental precedence modifiers SHOULD NOT alter the precedence by
   more than +-4.

   The system MAY automatically add depreference routes to global scope
   routing tables.  These routes will cover address space reserved for
   transition techniques, such as 2002::/16 (FIXME: add xrefs) and
   2001::/32.  They SHOULD have the same next-hop information as the
   default route in the same table, but their precedence SHOULD be 15.

   The system MAY automatically add blackhole routes to global scope
   routing tables for illegal address combinations.  An example of such
   an illegal combination is IPv6 prefix 2002:a00::/24, which
   corresponds to 6to4 addresses generated from IPv4 addresses inside
   10.0.0.0/8 which can't be used on the Internet.

3.1.3.  Transition Technique Routing Tables

   The default precedence for all route entries for source addresses
   generated through transition techniques SHOULD be 30.

   The transition table SHOULD NOT of course have a depreference route
   for its own address space.  Instead, the precedence of the route for
   its own address space SHOULD be 35.

   Individual transition techniques or the system administrator MAY



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   specify different default precedences to establish relative
   preferences between transition techniques or the proxies/servers
   associated with them.

3.1.4.  IPv4 Compatible Routing Tables

   The default precedence for all IPv4 compatible global scope route
   entries SHOULD be 20.

3.1.5.  Reachability Information

   If the next-hop information associated with a route in any table has
   been found unreachable or the interface link is down the precedence
   of that route MAY be temporarily dropped to zero until it works
   again.


4.  RFC3484 Rule Comparison

   The algorithm defined by [RFC3484] uses a set of rules to perform its
   function.  Those rules are compared to this algorithm in this
   section.

   FIXME: write this section


5.  RFC5220 Concerns

   [RFC5220] presents several problems and issues with the original
   default address selection algorithm.  The following subsections
   address these issues.

5.1.  Multiple Routers on a Single Interface

   This problem was one of the starting points for the development of
   this algorithm.  This algorithm solves the problem by having separate
   routing tables for addresses learned from different routers.

5.2.  Ingress Filtering Problem

   This problem was one of the starting points for the development of
   this algorithm.  This algorithm solves the problem by having separate
   routing tables for different addresses.

5.3.  Half-Closed Network Problem

   This problem was one of the starting points for the development of
   this algorithm.  This algorithm solves the problem by having separate



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   routing tables for different addresses.

   System or network administration MUST specify allowed or disallowed
   connections by modifying the routing tables.

5.4.  Combined Use of Global and ULA

   This algorithm solves the problem by having separate routing tables
   for different addresses.  Scope of address usage is controlled by the
   routing tables.

   Implementations MAY recognize ULA addresses and other site local
   addresses as scopes of their own, and treat them properly when
   autogenerating the routing tables.

   System or network administration MUST specify allowed or disallowed
   address pair selection by modifying the routing tables.

5.5.  Site Renumbering

   When the autoconfiguration client discovers that a prefix or address
   has been deprecated, it SHOULD drop the route precedences for all the
   routes associated with the deprecated resource to zero.

   When such deprecated routing information finally times out and is no
   longer in use, the routing table associated with it MAY be removed
   entirely.

5.6.  Multicast Source Address Selection

   TBD

5.7.  Temporary Address Selection

   Conceivably temporary addresses could be associated with routing
   tables of their own, instead of sharing routing tables with the
   addresses used to generate the temporary addresses.

   The precedences for the table for a temporary address would be lower
   than that of a similar but more permanent address.  Clients wishing
   to make use of the temporary address would add appropriate
   constraints to their address selection.

   Alternatively, if the system or network administration wishes that
   the host use a temporary address with some certain destination
   network, a route to that network could be added to the routing table
   for the temporary address with a higher than normal precedence.




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5.8.  IPv4 or IPv6 Prioritization

   This is a configuration issue with the routing tables.

   Connection pooling, as specified in Section 7.3, could mitigate this
   problem.

5.9.  ULA and IPv4 Dual-Stack Environment

   This special case is easily handled by omitting the default route for
   the routing table for ULA addresses.

5.10.  ULA or Global Prioritization

   Already covered in Section 5.4.


6.  RFC5221 Requirements

   [RFC5221] defines a set of requirements for the address selection
   algorithm.  The subsection headings used in that document have been
   copied here and an explanation of how this algorithm deals with each
   issue is given.

6.1.  Effectiveness

   The effectiveness of the proposed solution to solve problems
   presented in [RFC5220] is covered by Section 5.

6.2.  Timing

   This algorithm relies on other methods and protocols to submit
   address selection configuration and information and to place it in
   the routing table.

   Once the routing table is updated, the address selection algorithm
   will start making decisions based on the new information.

6.3.  Dynamic Behavior Update

   From the point of view of this algorithm, this problem is a feature
   of autoconfiguration methods.  If the autoconfiguration methods
   rewrite routing tables, the address selection algorithm will always
   use the updated information when it's invoked.







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6.4.  Node-Specific Behavior

   From the point of view of this algorithm, this problem is a feature
   of autoconfiguration methods.  This algorithm will happily make
   address selection decisions according to any input it is given.

6.5.  Application-Specific Behavior

   Additional filter constraints from Section 2.4 can be used to
   influence address selection per application.

6.6.  Multiple Interface

   This algorithm doesn't differenciate between cases where a host has
   multiple interfaces and where it has multiple prefixes on a single
   interface.  If it solves a problem satisfactorily for one case, it
   solves it identically for the other case as well.

6.7.  Central Control

   This algorithm doesn't specify new methods for central control.  It
   does, however, work well with other protocols that provide methods of
   central control, such as routing protocols.

6.8.  Next-Hop Selection

   The next-hop and interface used is a side product of the source
   address specific routing table lookup, which is performed in the
   filtering stage.

   A very pleasing feature of this algorithm is that there can be
   multiple routers advertising different prefixes on the same subnet,
   and this algorithm will still select proper address pairs and next-
   hops to satisfy any SAVI requirements.

6.9.  Compatibility with RFC 3493

   TBD

   On first impression, this algorithm shouldn't have any impact on the
   Socket API.  Then again, routing table index could be referenced as
   part of some process.

   Solaris, for example, creates new alias-interfaces for each new
   address assigned to a physical interface.  So if_index could also be
   used to uniquely identify a source address specific routing table on
   that platform.  Other operating systems do not work the same way.




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6.10.  Compatibility and Interoperability with RFC 3484

   When a host implementing this address selection algorithm and a host
   implementing the [RFC3484] algorithm interact, this algorithm will
   become constrained by the choices made by the peer.

6.11.  Security

   Security issues raised in [RFC5221] are covered by Section 10.2.


7.  Implementation Issues and Other Concerns

   Some popular operating systems already implement all the features
   required to implement this algorithm.  In such cases all that is
   required is to integrate the features together.

   The trickiest feature required by this algorithm is probably support
   for multiple routing tables.  This may also create backward
   compatibility issues in some implementations.  More discussion may be
   required here.

7.1.  Low Memory and Power Concerns

   The biggest worry is that creating lots of routing tables will waste
   memory and power.  However, when compared to the old way (see
   Appendix A), memory consumption doesn't explode.  Every route that
   was present in the monolithic routing table will usually be present
   in only one source address specific routing table.

   CGAs (ADD XREF) MAY reuse the same routing table.

7.2.  Differing Larger Scopes

   The default route for global scope addresses is 0::0/0, but this
   route will also cover addresses of potentially incompatible scopes.
   For example, the basic algorithm would accept a link local
   destination address with a global scope source address.

   One way to prevent this would be to add blackhole routes into the
   routing tables of global scope addresses for address space belonging
   to incompatible scopes.  The filter algorithm SHOULD treat a
   blackhole route as an indication that no valid route was found for
   addresses matching the blackhole in that table.







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7.3.  Connection Pooling

   When trying to establish a new connection, the stack MAY send open
   packets to all source/destination/nexthop combinations that pass the
   filter stage at a pace of three per second until it receives a
   response.

   When the connection is established the addresses are fixed (for non-
   multipathing protocols, such as TCP).

   If the peer also responds to the other connection attempts after the
   first connection is established, those connections MAY either be
   reset immediately, or the stack MAY pool them for a short while in an
   incomplete handshake state, in case some application tries to open an
   identical socket.

   This would benefit applications such as web browsers, mail transfer
   agents and database clients, which routinely create more than one
   connection between the same two hosts and the same destination port.

   It would also benefit dual stacked or multi-homed hosts where some of
   the addresses or networks are misconfigured and don't work.

7.4.  Using Just One Table with Tags

   It is possible to implement this algorithm with just one routing
   table, if tags or bitfields are used to identify which routing table
   each route really belongs to.

   However, since a less specific route in one table can have higher
   precedence than a more specific route in another table, care must be
   taken in the implementation.

   It is also possible to implement this algorithm without interfering
   with the actual routing table at all, by just mirroring all the
   routing table information and changes in a policy table used by this
   algorithm only.


8.  Acknowledgements

   This document was written using the template derived from an initial
   version written by Pekka Savola and contributed by him to the xml2rfc
   project.

   Thanks to the following people for giving feedback during the writing
   of this document: Jari Arkko, Jan Melen, Arifumi Matsumoto, James
   Morse, .



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9.  IANA Considerations

   This document has no IANA Actions.


10.  Security Considerations

10.1.  RFC5220 Considerations

   Section 4 of [RFC5220] raises a concern that a malicious attacker can
   gather information about addresses connected to the target host by
   triggering the address selection algorithm on the target host by
   various methods and listening to what candidates it produces.

   This algorithm doesn't completely remove that possibility, but due to
   the filtering stage, the attacker can only gain information on
   addresses routable to the address used by the attacker.

10.2.  RFC5221 Requirements

   Section 3 of [RFC5221] lists two security concerns which are dealt
   with in subsections below.

10.2.1.  List of threats introduced by new address-selection mechanism

   This specification relies on existing autoconfiguration methods and
   routing protocols to distribute address selection hints.  Each of
   those SHOULD have their own methods to combat leakage, hijacking and
   denial of service.

10.2.2.  List of recommendations in which security mechanism should be
         applied

   This specification relies on existing autoconfiguration methods and
   routing protocols to distribute address selection hints.  Each of
   those SHOULD have their own methods to combat leakage, hijacking and
   denial of service.


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.

   [RFC2960]  Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
              Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,



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              Zhang, L., and V. Paxson, "Stream Control Transmission
              Protocol", RFC 2960, October 2000.

   [RFC3442]  Lemon, T., Cheshire, S., and B. Volz, "The Classless
              Static Route Option for Dynamic Host Configuration
              Protocol (DHCP) version 4", RFC 3442, December 2002.

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

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

   [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.

11.2.  Informative References

   [I-D.blanchet-mif-problem-statement]
              Blanchet, M. and P. Seite, "Multiple Interfaces Problem
              Statement", draft-blanchet-mif-problem-statement-01 (work
              in progress), June 2009.

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


Appendix A.  Routing Table Example

   This section demonstrates how this algorithm affects the routing
   table of a multi-homed host.  Appendix A.1 shows the routing table
   using only methods without this algorithm.  Appendix A.2 shows the
   routing tables produced on the same host if this algorithm is
   applied.

A.1.  Before

   This routing table was initially copied from a system running Linux
   2.6.25.  The addresses were then greatly simplified to make the table
   fit better on the page.




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      +--------------------------------+----------+--------+--------+
      | Network                        | Next-Hop | Link   | Metric |
      +--------------------------------+----------+--------+--------+
      | 2001::/32                      | ::       | teredo | 256    |
      | 2001:db8:1::/64                | ::       | eth0   | 256    |
      | 2001:db8:2::/64                | ::       | eth1   | 256    |
      | fe80::/64                      | ::       | teredo | 256    |
      | fe80::/64                      | ::       | eth0   | 256    |
      | fe80::/64                      | ::       | eth1   | 256    |
      | ::/0                           | ::       | teredo | 1029   |
      | ::/0                           | fe80::13 | eth0   | 1024   |
      | ::/0                           | fe80::ce | eth1   | 1024   |
      | ::/0                           | ::       | lo     | -1 !U  |
      | ::1/128                        | ::       | lo     | 0      |
      | 2001:db8:1:0:a00:ff:fedc:a/128 | ::       | lo     | 0      |
      | 2001:db8:2:0:200:ff:fec4:b/128 | ::       | lo     | 0      |
      | 2001:0:c200:201::3/128         | ::       | lo     | 0      |
      | fe80::a00:ff:fedc:a/128        | ::       | lo     | 0      |
      | fe80::200:ff:fec4:b/128        | ::       | lo     | 0      |
      | fe80::ffff:ffff:ffff/128       | ::       | lo     | 0      |
      +--------------------------------+----------+--------+--------+

                 Table 1: Routing Table w/o Modifications

   "!U" after metric denotes unreachable or blackhole routes.

A.2.  After Conversion

   These tables contain and implement just the basic idea.  Thus the
   combined size of these tables is equal to Table 1.  Optional
   improvements are presented in the next subsection.

                  +---------+----------+------+--------+
                  | Network | Next-Hop | Link | Metric |
                  +---------+----------+------+--------+
                  | ::/0    | ::       | lo   | -1 !U  |
                  | ::1/128 | ::       | lo   | 50     |
                  +---------+----------+------+--------+

                      Table 2: Routing Table for ::1











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          +------------------------+----------+--------+--------+
          | Network                | Next-Hop | Link   | Metric |
          +------------------------+----------+--------+--------+
          | 2001::/32              | ::       | teredo | 35     |
          | ::/0                   | ::       | teredo | 30     |
          | 2001:0:c200:201::3/128 | ::       | lo     | 50     |
          +------------------------+----------+--------+--------+

           Table 3: Routing Table for 2001:0:c200:201::3%teredo

         +--------------------------+----------+--------+--------+
         | Network                  | Next-Hop | Link   | Metric |
         +--------------------------+----------+--------+--------+
         | fe80::/64                | ::       | teredo | 50     |
         | fe80::ffff:ffff:ffff/128 | ::       | lo     | 50     |
         +--------------------------+----------+--------+--------+

          Table 4: Routing Table for fe80::ffff:ffff:ffff%teredo

       +--------------------------------+----------+------+--------+
       | Network                        | Next-Hop | Link | Metric |
       +--------------------------------+----------+------+--------+
       | 2001:db8:1::/64                | ::       | eth0 | 40     |
       | ::/0                           | fe80::13 | eth0 | 40     |
       | 2001:db8:1:0:a00:ff:fedc:a/128 | ::       | lo   | 50     |
       +--------------------------------+----------+------+--------+

        Table 5: Routing Table for 2001:db8:1:0:a00:ff:fedc:a%eth0

          +-------------------------+----------+------+--------+
          | Network                 | Next-Hop | Link | Metric |
          +-------------------------+----------+------+--------+
          | fe80::/64               | ::       | eth0 | 50     |
          | fe80::a00:ff:fedc:a/128 | ::       | lo   | 50     |
          +-------------------------+----------+------+--------+

            Table 6: Routing Table for fe80::a00:ff:fedc:a%eth0

       +--------------------------------+----------+------+--------+
       | Network                        | Next-Hop | Link | Metric |
       +--------------------------------+----------+------+--------+
       | 2001:db8:2::/64                | ::       | eth1 | 40     |
       | 2001:db8:2:0:200:ff:fec4:b/128 | ::       | lo   | 50     |
       | ::/0                           | fe80::ce | eth1 | 40     |
       +--------------------------------+----------+------+--------+

        Table 7: Routing Table for 2001:db8:2:0:200:ff:fec4:b%eth1




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          +-------------------------+----------+------+--------+
          | Network                 | Next-Hop | Link | Metric |
          +-------------------------+----------+------+--------+
          | fe80::/64               | ::       | eth1 | 50     |
          | fe80::200:ff:fec4:b/128 | ::       | lo   | 50     |
          +-------------------------+----------+------+--------+

            Table 8: Routing Table for fe80::200:ff:fec4:b%eth1


Author's Address

   Aleksi Suhonen
   Tampere University of Technology, Finland
   Korkeakoulunkatu 1
   Tampere  33720
   FI

   Phone: +358 45 670 2048
   Email: i-d-2009@ssd.axu.tm































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