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Versions: 00 01

Network Working Group                                         P. Pfister
Internet-Draft                                             Cisco Systems
Updates: 4191 (if approved)                                June 22, 2015
Intended status: Standards Track
Expires: December 24, 2015


      Source Address Dependent Route Information Option for Router
                             Advertisements
                     draft-pfister-6man-sadr-ra-01

Abstract

   This document defines the Source Address Dependent Route Information
   option for Router Advertisements, enabling source address dependent
   routes to be installed in hosts by neighboring routers.  It also adds
   a new flag to the existing Route Information option for backward
   compatibility purposes.

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
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   This Internet-Draft will expire on December 24, 2015.

Copyright Notice

   Copyright (c) 2015 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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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Source Address Dependent Route Information Option . . . . . .   3
   3.  Route Information Option ignore flag  . . . . . . . . . . . .   4
   4.  Host Behavior . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Selecting the next-hop router . . . . . . . . . . . . . .   6
     4.2.  Receiving Source Address Dependent Route Information
           option  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  Receiving Route Information options . . . . . . . . . . .   7
   5.  Router Behavior . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Hosts may have multiple non-link-local addresses, possibly provided
   by different routers located on one or multiple links.  In such
   situations, hosts must make sure packets with a given source address
   are sent to the right next-hop router.  Failing in selecting the
   right next-hop router may, at best, induce sub-optimal routing and,
   at worst, cause the packet to be dropped ([RFC2827]).  Rules 5 and
   5.5 from the default address selection algorithm [RFC6724] make sure
   that, once the next-hop is chosen, care is taken to pick the right
   source address.  Nevertheless, these rules may fail in some
   situations, e.g., when the same prefix is advertised on the same link
   by different routers.  Additionally, they don't handle situations
   where the application picks the source-address before sending the
   packet.

   This document defines the Source Address Dependent Route Information
   Option for Router Advertisements [RFC4861], enabling source address
   dependent routes to be installed in hosts by neighboring routers.  It
   also adds a new flag to the Route Information Option meaning that the
   option may be ignored by hosts implementing this specification.








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2.  Source Address Dependent Route Information Option

   This section defines a new Router Advertisement option called the
   Source Address Dependent Route Information option.  Its use is
   similar to the Route Information option defined in [RFC4191] but also
   includes additional source prefix fields, allowing source address
   dependent routes to be installed on hosts receiving the Router
   Advertisement.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |   Dst Length  |Resvd|Prf|Resvd|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Route Lifetime                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .               Destination Prefix (Variable Length)            .
   .                                                               .
   .                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                               |   Src Length  |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
   |                                                               |
   .                 Source Prefix (Variable Length)               .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Source Address Dependent Route Information Option

   Type:  To be defined by IANA.

   Length:  The length of the option (including the Type and Length
      fields) in units of 8 octets.  It ranges from 2 to 6.

   Dst Length:  The number of significant bits in the Destination Prefix
      field.

   Resvd (Reserved):  Bits reserved for futur use.  They MUST be set to
      zero by the sender and ignored by the receiver.

   Prf (Route Preference):  The route preference as specified in
      [RFC4191].  When the Reserved value (10) is received, the option
      MUST be ignored.

   Route Lifetime:  Time in seconds (relative to the time the packet is
      sent) that the prefix is valid for route determination.  A value
      of all one bits (0xffffffff) represents infinity.




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   Destination Prefix:  The destination prefix significant bits padded
      to the next 8-bits boundary.

   Src Length:  The number of significant bits in the Source Prefix
      field.

   Source Prefix:  The source prefix significant bits padded to the next
      64-bits boundary.

   The following C code is given as an help for implementation:

       #define ALIGN(bitlength, alignment) \
           (((bitlength != 0)?(((bitlength - 1) / alignment) + 1):0) * \
                 (alignment / 8))

       unsigned char *option;
       size_t src_len_index = 8 + ALIGN(option[2], 8);
       size_t total_byte_length = ALIGN((src_len_index + 1) * 8
                                  + option[src_len_index], 64);

   Note: Comments have been made regarding address alignment.  There is
   no format providing at the same time good alignment and optimal TLV
   size, while aligning both source and destination prefixes would waste
   from 7 to 21 bytes per option.  This TLV format is proposed based on
   implementation experience and provides both TLV size efficiency, and
   relative compatibility with the Route Information option (Linux
   implementation of this option support is less than 100 lines of
   code).

   Comments and propositions are welcome regarding which format to
   adopt.

3.  Route Information Option ignore flag

   This document adds the Ignore flag to the Route Information option
   specified in [RFC4191].  It is used in order to configure type C
   hosts with more specific routes which will be ignored by hosts
   implementing this specification.  Most of the time, such options with
   the I bit set will be used in conjunction with Source Address
   Dependent Route Information options including the same or a similar
   destination prefix.










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   The option is re-defined with an additional flag.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     | Prefix Length |I|Rsv|Prf|Resvd|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Route Lifetime                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Prefix (Variable Length)                    |
   .                                                               .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Route Information Option

   I flag:  Ignore flag.  When this flag is set, the option MUST be
      ignored.

   Other fields:  No changes (see [RFC4191]).

4.  Host Behavior

   Hosts implementing this specification are referred to as type D
   hosts, in reference to host types A, B and C defined in [RFC4191].
   As a reminder, type A hosts are hosts behaving as specified in
   [RFC4191].  Type B hosts behave similarly to type A hosts with the
   addition that they act upon the Default Router Preference values
   present in Router Advertisement headers.  Finally, type C hosts
   behave as type B hosts with the addition that they act upon received
   Route Information Options.

   This section specifies type D hosts behavior.  Type D hosts MUST
   behave as type C hosts unless stated otherwise in this section.  For
   the sake of clarity, in this whole section, 'host' refers to 'type D
   host'.

   Hosts MUST use a Routing Table with source address dependent entries.
   Such entries have a:

   o  Source prefix

   o  Destination prefix

   o  Preference value

   o  Interface




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   o  Next-hop router address

   o  Lifetime and associated timer

4.1.  Selecting the next-hop router

   When sending a packet, hosts MUST select the next-hop router based on
   the usual source address dependent routing algorithm, i.e., by
   picking the matching entry with, by order of precedence:

      The longest destination address match.

      The longest source address match.

      The greatest route preference value.

   In case of a tie, hosts MAY either pick one entry or use load-sharing
   techniques.

4.2.  Receiving Source Address Dependent Route Information option

   When receiving a Source Address Dependent Route Information option, a
   host MUST look for an existing routing entry with:

   1.  The same source prefix.

   2.  The same destination prefix.

   3.  The next-hop router address equal to the source address of the
       received Router Advertisement.

   4.  The outgoing interface equal to the interface the Router
       Advertisement is received on.

   If no routing entry is found and the Route Lifetime is not null,
   insert a routing entry with the given source prefix, destination
   prefix, route preference, having as next-hop the source address of
   the received Router Advertisement, on the interface receiving the
   packet.  If the Route Lifetime is not infinity, set the routing entry
   timer to the Route Lifetime value.

   If a routing entry is found and the Route Lifetime is not null,
   cancel the associated timer.  If the Route Lifetime is not infinity,
   set the timer to the Route Lifetime value.  Finally, update the entry
   preference with the Route Preference value.

   If a routing entry is found and the Route Lifetime is null, remove
   the routing entry.



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   If both destination and source prefixes specified by the option are
   ::/0, the router preference and route lifetime present in the option
   overrides the default router lifetime and default router preference
   present in the header of the Router Advertisement.

4.3.  Receiving Route Information options

   When receiving a Route Information option, a host MUST behave as
   follows:

      If the I bit is set, ignore the option.

      Otherwise, act as when receiving a Source Address Dependent Route
      Information option with source prefix length set to zero.

5.  Router Behavior

   Routers MAY send one or multiple Source Address Dependent Route
   Information options in their Router Advertisements.

   Routers MUST NOT send multiple Route Information options with the
   same Prefix (no matter what the Ignore flag value is) or multiple
   Source Address Dependent Route Information options with the same
   Source and Destination Prefixes.  Additionally, routers MUST NOT send
   a Route Information option with the Ignore bit not set and a Source
   Address Dependent Route Information with the source length equal to
   zero if the Prefix from the Route Information option is equal to the
   Destination Prefix from the Source Address Dependent Route
   Information option.

   The Ignore bit is used to configure type D hosts differently from
   hosts of types A, B or C. Different combinations will result in
   different behaviors.  For instance:

      When injecting a source address dependent route is desired, a
      Source Address Dependent Route Information option is sent in every
      RA.  Depending on the context, a Route Information with the same
      prefix and the Ignore bit set MAY be sent as well in order to
      inject a non source address dependent route into type C hosts.
      Obviously, Source Address Dependent Route Information options can
      be used to inject non-source dependent routes as well.  This
      technique and the use of the Ignore bit allow type C hosts and
      type D hosts to be configured with possibly independent routes.

      When injecting a non source address dependent route is desired,
      the router MAY either use a Route Information option with the
      Ignore flag not set, in which case both type C and D hosts will be
      configured, or use a Source Address Dependent Route Information



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      option with a source prefix ::/0, in which case type C hosts will
      not be configured.

   When a Source Address Dependent Route Information option is removed
   from the set of advertised options, or when the interface ceases to
   be an advertising interface, the router SHOULD send up to
   MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited Router Advertisements,
   using the same rule as in [RFC2461], with the Route Lifetime set to
   zero in all Source Address Dependent Route Information options that
   have become invalid.

6.  Security Considerations

   This document allows routers to configure neighboring hosts with
   source address dependent routing entries.  Based on [RFC4191],
   attackers can inject default routes to type A and B hosts as well as
   destination address dependent routes to type C hosts.  The Source
   Address Dependent Route Information option adds the ability for
   attackers to inject even more specific routes, making attacks
   slightly harder to detect.

7.  IANA Considerations

   IANA is kindly asked to reserve a Router Advertisement option type to
   be used by the Source Address Dependent Route Information option.

8.  Acknowledgments

   The author would appreciate reviews and comments.

9.  References

9.1.  Normative References

   [RFC2461]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor
              Discovery for IP Version 6 (IPv6)", RFC 2461, December
              1998.

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

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







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9.2.  Informative References

   [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.

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

Author's Address

   Pierre Pfister
   Cisco Systems
   Paris
   France

   Email: pierre.pfister@darou.fr

































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