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Versions: (draft-cheng-ospf-ipv4-embedded-ipv6-routing) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 6992

Network Working Group                                           D. Cheng
Internet-Draft                                       Huawei Technologies
Intended status: Informational                              M. Boucadair
Expires: December 13, 2013                                France Telecom
                                                               A. Retana
                                                           Cisco Systems
                                                           June 11, 2013


                 Routing for IPv4-embedded IPv6 Packets
             draft-ietf-ospf-ipv4-embedded-ipv6-routing-14

Abstract

   This document describes a routing scenario where IPv4 packets are
   transported over an IPv6 network, based on RFCs 6145 and 6052, along
   with a separate OSPFv3 routing table for IPv4-embedded IPv6 routes in
   the IPv6 network.

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 December 13, 2013.

Copyright Notice

   Copyright (c) 2013 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
   (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
   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
     1.1.  The Scenario  . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Routing Solution per RFC5565  . . . . . . . . . . . . . .   4
     1.3.  An Alternative Routing Solution with OSPFv3 . . . . . . .   4
     1.4.  OSPFv3 Routing with a Specific Topology . . . . . . . . .   6
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   6
   3.  Provisioning  . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Deciding the IPv4-embedded IPv6 Topology  . . . . . . . .   6
     3.2.  Maintaining a Dedicated IPv4-embedded IPv6 Routing Table    7
   4.  IP Packets Translation  . . . . . . . . . . . . . . . . . . .   8
     4.1.  Address Translation . . . . . . . . . . . . . . . . . . .   8
   5.  Advertising IPv4-embedded IPv6 Routes . . . . . . . . . . . .   8
     5.1.  Advertising IPv4-embedded IPv6 Routes through an IPv6
           Transit Network . . . . . . . . . . . . . . . . . . . . .   9
       5.1.1.  Routing Metrics . . . . . . . . . . . . . . . . . . .   9
       5.1.2.  Forwarding Address  . . . . . . . . . . . . . . . . .   9
     5.2.  Advertising IPv4 Addresses into Client Networks . . . . .   9
   6.  Aggregation on IPv4 Addresses and Prefixes  . . . . . . . . .  10
   7.  Forwarding  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  Backdoor Connections  . . . . . . . . . . . . . . . . . . . .  11
   9.  Prevention of Loops . . . . . . . . . . . . . . . . . . . . .  11
   10. MTU Issues  . . . . . . . . . . . . . . . . . . . . . . . . .  11
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  11
   12. Operational Considerations  . . . . . . . . . . . . . . . . .  12
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     15.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   This document describes a routing scenario where IPv4 packets are
   transported over an IPv6 network, based on [RFC6145] and [RFC6052],
   along with a separate OSPFv3 routing table for IPv4-embedded IPv6
   routes in the IPv6 network.  This document does not introduce any new
   IPv6 transition mechanism.

   In this document the following terminology is used:






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   o  An IPv4-embedded IPv6 address denotes an IPv6 address which
      contains an embedded 32-bit IPv4 address constructed according to
      the rules defined in [RFC6052].

   o  IPv4-embedded IPv6 packets are packets of which destination
      addresses are IPv4-embedded IPv6 addresses.

   o  AFBR (Address Family Border Router, [RFC5565]) refers to an edge
      router, which supports both IPv4 and IPv6 address families, but
      the backbone network it connects to only supports either the IPv4
      or IPv6 address family.

   o  AFXLBR (Address Family Translation Border Router) is defined in
      this document.  It refers to a border router that supports both
      IPv4 and IPv6 address families, located on the boundary of an
      IPv4-only network and an IPv6-only network, and is capable of
      performing IP header translation between IPv4 and IPv6 according
      to [RFC6145].

1.1.  The Scenario

   Due to exhaustion of public IPv4 addresses, there has been a
   continuing effort within the IETF on IPv6 transitional techniques.
   In the course of the transition, it is certain that networks based on
   IPv4 and IPv6 technologies respectively, will co-exist at least for
   some time.  One scenario of this co-existence is the inter-connection
   of IPv4-only and IPv6-only networks, and in particular, when an
   IPv6-only network serves as inter-connection between several
   segregated IPv4-only networks.  In this scenario, IPv4 packets are
   transported over the IPv6 network between IPv4 networks.  In order to
   forward an IPv4 packet from a source IPv4 network to the destination
   IPv4 network, IPv4 reachability information must be exchanged between
   the IPv4 networks by some mechanism.

   In general, running an IPv6-only network would reduce operational
   expenditure and optimize the operation compared to IPv4-IPv6 dual-
   stack environment.  Some solutions have been proposed to allow
   delivery of IPv4 services over an IPv6-only network.  This document
   specifies an engineering technique that separates the routing table
   dedicated to IPv4-embedded IPv6 destinations from the routing table
   used for native IPv6 destinations.

   OSPFv3 is designed to support multiple instances.  Maintaining a
   separate routing table for IPv4-embedded IPv6 routes would simplify
   the implementation, trouble shooting and operation; it also prevents
   overload of the native IPv6 routing table.  A separate routing table
   can be generated from a separate routing instance.




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1.2.  Routing Solution per RFC5565

   The aforementioned scenario is described in [RFC5565], i.e., IPv4
   -over-IPv6 scenario, where the network core is IPv6-only, and the
   inter-connected IPv4 networks are called IPv4 client networks.  The
   P(rovider) Routers in the core only support IPv6 but the AFBRs
   (Address Family Border Routers) support IPv4 on interfaces facing
   IPv4 client networks, and IPv6 on interfaces facing the core.  The
   routing solution defined in [RFC5565] for this scenario is to run
   i-BGP among AFBRs to exchange IPv4 routing information in the core,
   and the IPv4 packets are forwarded from one IPv4 client network to
   the other through a softwire using tunneling technology such as MPLS
   LSP, GRE, L2TPv3, etc.

1.3.  An Alternative Routing Solution with OSPFv3

   In this document, we propose an alternative routing solution for the
   scenario described in Section 1.1, where several segregated IPv4
   networks, called IPv4 client networks, are inter-connected by an IPv6
   network.  The IPv6 network and the inter-connected IPv4 networks may
   or may not belong to the same Autonomous System.  We refer to the
   border node on the boundary of an IPv4 client network and the IPv6
   network as an Address Family Translation Border Router (AFXLBR),
   which supports both the IPv4 and IPv6 address families, and is
   capable of translating an IPv4 packet to an IPv6 packet, and vice
   versa, according to [RFC6145].  The described scenario is illustrated
   in Figure 1.



                    +--------+   +--------+
                    |  IPv4  |   |  IPv4  |
                    | Client |   | Client |
                    | Network|   | Network|
                    +--------+   +--------+
                        |   \     /   |
                        |    \   /    |
                        |     \ /     |
                        |      X      |
                        |     / \     |
                        |    /   \    |
                        |   /     \   |
                    +--------+   +--------+
                    | AFXLBR |   | AFXLBR |
                 +--| IPv4/6 |---| IPv4/6 |--+
                 |  +--------+   +--------+  |
   +--------+    |                           |    +--------+
   |  IPv6  |    |                           |    |  IPv6  |



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   | Client |----|                           |----| Client |
   | Network|    |            IPv6           |    | Network|
   +--------+    |            only           |    +--------+
                 |                           |
                 |  +--------+   +--------+  |
                 +--| AFXLBR |---| AFXLBR |--+
                    | IPv4/6 |   | IPv4/6 |
                    +--------+   +--------+
                        |   \     /   |
                        |    \   /    |
                        |     \ /     |
                        |      X      |
                        |     / \     |
                        |    /   \    |
                        |   /     \   |
                    +--------+   +--------+
                    |  IPv4  |   |  IPv4  |
                    | Client |   | Client |
                    | Network|   | Network|
                    +--------+   +--------+


   Figure 1: Segregated IPv4 Networks Inter-connected by an IPv6 Network

   Since the scenario occurs most commonly within an organization, an
   IPv6 prefix can be locally allocated and used by AFXLBRs to construct
   IPv4-embedded IPv6 addresses according to [RFC6052].  The embedded
   IPv4 address or prefix belongs to an IPv4 client network that is
   connected to the AFXLBR.  An AFXLBR injects IPv4-embedded IPv6
   addresses and prefixes into the IPv6 network using OSPFv3, and it
   also installs IPv4-embedded IPv6 routes advertised by other AFXLBRs.

   When an AFXLBR receives an IPv4 packet from a locally connected IPv4
   client network and destined to a remote IPv4 client network, it
   translates the IPv4 header to the relevant IPv6 header according to
   [RFC6145], and in that process, source and destination IPv4 address
   are translated into IPv4-embedded IPv6 addresses, respectively,
   according to [RFC6052].  The resulting IPv6 packet is then forwarded
   to the AFXLBR that connects to the destination IPv4 client network.
   The remote AFXLBR derives the IPv4 source and destination addresses
   from the IPv4-embedded IPv6 addresses, respectively, according to
   [RFC6052], and translates the header of the received IPv6 packet to
   the relevant IPv4 header according to [RFC6145].  The resulting IPv4
   packet is then forwarded according to the IPv4 routing table
   maintained on the AFXLBR.

   There are use cases where the proposed routing solution is useful.
   One case is that some border nodes do not participate in i-BGP for



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   routes exchange, or i-BGP is not used at all.  Another case is when
   tunnels are not deployed in the IPv6 network, or native IPv6
   forwarding is preferred.  Note that with this routing solution, the
   IPv4 and IPv6 header translation performed in both directions by the
   AFXLBR is stateless.

1.4.  OSPFv3 Routing with a Specific Topology

   In general, IPv4-embedded IPv6 packets can be forwarded just like
   native IPv6 packets with OSPFv3 running in the IPv6 network.
   However, this would require IPv4-embedded IPv6 routes be flooded
   throughout the entire IPv6 network and stored on every router.  This
   is not desirable from the scaling perspective.  Moreover, since all
   IPv6 routes are stored in the same routing table, it would be
   inconvenient to manage the resource required for routing and
   forwarding based on traffic category, if so desired.

   To improve the situation, a separate OSPFv3 routing table can be
   constructed that is dedicated to the IPv4-embedded IPv6 topology, and
   that table is solely used for routing IPv4-embedded IPv6 packets in
   the IPv6 network.  The IPv4-embedded IPv6 topology includes all the
   participating AFXLBR routers and a set of P Routers providing
   redundant connectivity with alternate routing paths.

   To realize this, a separate OSPFv3 instance is configured in the IPv6
   network according to [RFC5838].  This instance operates on all
   participating AFXLBR and a set of P routers that inter-connecting
   them.  As a result, there would be a dedicated IPv4-embedded IPv6
   topology that is maintained on all these routers along with a
   dedicated IPv4-embedded IPv6 routing table.  This routing table in
   the IPv6 network is solely for forwarding IPv4-embedded IPv6 packets.

   This document elaborates on how configuration is done with this
   method and related routing issues.

   This document only focuses on unicast routing for IPv4-embedded IPv6
   packets using OSPFv3.

2.  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 [RFC2119].

3.  Provisioning

3.1.  Deciding the IPv4-embedded IPv6 Topology




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   Before deploying configurations that use a separate OSPFv3 routing
   table for IPv4-embedded IPv6 addresses and prefixes, a decision must
   be made on the set of routers and their interfaces in the IPv6
   network that should be part of the IPv4-embedded IPv6 topology.

   For the purpose of this IPv4-embedded IPv6 topology, all AFXLBRs that
   connect to IPv4 client networks MUST be members of this topology.  An
   AFXLBR MUST have at least one connection with a P Router in the IPv6
   network or another AFXLBR.

   The IPv4-embedded IPv6 topology is a sub-topology of the entire IPv6
   network, and if all routers (including AFXLBRs and P routers) and all
   their interfaces are included, the two topologies converge.
   Generally speaking, when this sub-topology contains more inter-
   connected P Routers, there would be more routing paths across the
   IPv6 network from one IPv4 client network to the other; however, this
   requires more routers in the IPv6 network to participate in
   IPv4-embedded IPv6 routing.  In any case, the IPv4-embedded IPv6
   topology MUST be continuous with no partitions.

3.2.  Maintaining a Dedicated IPv4-embedded IPv6 Routing Table

   In an IPv6 network, in order to maintain a separate IPv6 routing
   table that contains routes for IPv4-embedded IPv6 destinations only,
   OSPFv3 needs to use the mechanism defined in [RFC5838].

   It is assumed that the IPv6 network that is inter-connected with IPv4
   networks in this document is under one administration and as such, an
   OSPFv3 instance ID (IID) is allocated locally and used for OSPFv3
   operation dedicated to unicast IPv4-embedded IPv6 routing in an IPv6
   network.  This IID is configured on OSPFv3 router interfaces that
   participate in the IPv4-embedded IPv6 topology.

   The range for a locally configured OSPFv3 IID is allocated from 192
   to 255, inclusive, as "Private Use" per
   [I-D.ietf-ospf-ospfv3-iid-registry-update].  This IID must be used to
   encode the "Instance ID" field in the packet header of OSPFv3 packets
   associated with the OSPFv3 instance.

   In addition, the "AF" bit in the OSPFv3 Option field MUST be set.

   During Hello packet processing, an adjacency may only be established
   when the received Hello packet contains the same Instance ID as
   configured on the receiving OSPFv3 interface.  This insures that only
   interfaces configured as part of the OSPFv3 unicast IPv4-embedded
   IPv6 topology are used for IPv4-embedded IPv6 unicast routing.

   For more details, the reader is referred to [RFC5838].



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4.  IP Packets Translation

   When transporting IPv4 packets across an IPv6 network with the
   mechanism described above (Section 3.2), an IPv4 packet is translated
   to an IPv6 packet at the ingress AFXLBR, and the IPv6 packet is
   translated back to an IPv4 packet at the egress AFXLBR.  The IP
   packet header translation is accomplished in stateless manner
   according to rules specified in [RFC6145], with the address
   translation details explained in the next sub-section.

4.1.  Address Translation

   Prior to address translation, an IPv6 prefix is allocated by the
   operator and it is used to form IPv4-embedded IPv6 addresses.

   The IPv6 prefix can either be the well-known IPv6 prefix (WKP)
   64:ff9b::/96, or a network-specific prefix that is unique to the
   organization; and for the latter case, the IPv6 prefix length may be
   32, 40, 48, 56 or 64.  In either case, this IPv6 prefix is used
   during the address translation between an IPv4 address and an
   IPv4-embedded IPv6 address, as described in [RFC6052].

   During translation from an IPv4 header to an IPv6 header at an
   ingress AFXLBR, the source IPv4 address and destination IPv4 address
   are translated into the corresponding IPv6 source address and
   destination IPv6 address, respectively, and during translation from
   an IPv6 header to an IPv4 header at an egress AFXLBR, the source IPv6
   address and destination IPv6 address are translated into the
   corresponding IPv4 source address and destination IPv4 address,
   respectively.  Note that the address translation is accomplished in a
   stateless manner.

   When a well-known IPv6 prefix (WKP) is used, [RFC6052] allows only
   global IPv4 addresses to be embedded in the IPv6 address.  An IPv6
   address composed with a WKP and a non-global IPv4 address is hence
   invalid, and packets that contain such address received by an AFXLBR
   are dropped.

   In the case where both the IPv4 client networks and the IPv6 transit
   network belong to the same organization, non-global IPv4 addresses
   may be used with a network-specific prefix [RFC6052].

5.  Advertising IPv4-embedded IPv6 Routes

   In order to forward IPv4 packets to the proper destination across an
   IPv6 network, IPv4 reachability needs to be disseminated throughout
   the IPv6 network and this is performed by AFXLBRs that connect to
   IPv4 client networks using OSPFv3.



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   With the scenario described in this document, i.e., a set of AFXLBRs
   that inter-connect a bunch of IPv4 client networks with an IPv6
   network, the IPv4 networks and IPv6 networks belong to the same or
   separate Autonomous Systems, and as such, these AFXLBRs behave as AS
   Boundary Routers (ASBRs).

5.1.  Advertising IPv4-embedded IPv6 Routes through an IPv6 Transit
      Network

   IPv4 addresses and prefixes in an IPv4 client network are translated
   into IPv4-embedded IPv6 addresses and prefixes, respectively, using
   the IPv6 prefix allocated by the operator and the method specified in
   [RFC6052].  These routes are then advertised by one or more attached
   ASBRs into the IPv6 transit network using AS-External-LSAs [RFC5340],
   i.e., with advertising scope comprising the entire Autonomous System.

5.1.1.  Routing Metrics

   By default, the metric in an AS-External-LSA that carries an
   IPv4-embedded IPv6 address or prefixes is a Type 1 external metric,
   which is comparable to the link state metric and we assume that in
   most cases, OSPFv2 is used in client IPv4 networks.  This metric is
   added to the metric of the intra-AS path to the ASBR during the
   OSPFv3 route calculation.  Through ASBR configuration, the metric can
   be set to a Type 2 external metric, which is considered much larger
   than the metric for any intra-AS path.  Refer to the OSPFv3
   specification [RFC5340] for more detail.  In either case, an external
   metric may take the same value as in an IPv4 network (using OSPFv2 or
   another routing protocol), but may also be specified based on some
   routing policy; the details of which are outside of the scope of this
   document.

5.1.2.  Forwarding Address

   If the "Forwarding Address" field of an OSPFv3 AS-External-LSA is
   used to carry an IPv6 address, that must also be an IPv4-embedded
   IPv6 address where the embedded IPv4 address is the destination
   address in an IPv4 client network.  However, since an AFXLBR sits on
   the border of an IPv4 network and an IPv6 network, it is RECOMMENDED
   that the "Forwarding Address" field is not used, so that the AFXLBR
   can make the forwarding decision based on its own IPv4 routing table.

5.2.  Advertising IPv4 Addresses into Client Networks

   IPv4-embedded IPv6 routes injected into the IPv6 network from one
   IPv4 client network MAY be advertised into another IPv4 client
   network, after the associated destination addresses and prefixes are
   translated back to IPv4 addresses and prefixes, respectively.  This



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   operation is similar to normal OSPFv3 operation, wherein an AS-
   External-LSA can be advertised in a non-backbone area by default.

   An IPv4 client network can limit which advertisements it receives
   through configuration.

   For the purpose of this document, IPv4-embedded IPv6 routes MUST NOT
   be advertised into any IPv6 client networks that also connected to
   the IPv6 transit network.

6.  Aggregation on IPv4 Addresses and Prefixes

   In order to reduce the amount of LSAs that are injected to the IPv6
   network, an implementation should provide mechanisms to aggregate
   IPv4 addresses and prefixes at AFXLBR prior to advertisement as
   IPv4-embedded IPv6 addresses and prefixes.  In general, the
   aggregation practice should be based on routing policy, which is
   outside of the scope of this document.

7.  Forwarding

   There are three cases in forwarding IP packets in the scenario
   described in this document:

   1.  On an AFXLBR, if an IPv4 packet that is received on an interface
       connecting to an IPv4 segregated client network with a
       destination IPv4 address belonging to another IPv4 client
       network, the header of the packet is translated to the
       corresponding IPv6 header as described in Section 4, and the
       packet is then forwarded to the destination AFXLBR that
       advertised the IPv4-embedded IPv6 address into the IPv6 network.

   2.  On an AFXLBR, if an IPv4-embedded IPv6 packet is received and the
       embedded destination IPv4 address is in its IPv4 routing table,
       the header of the packet is translated to the corresponding IPv4
       header as described in Section 4, and the packet is then
       forwarded accordingly.

   3.  On any router that is within the IPv4-embedded IPv6 topology
       subset of the IPv6 network, if an IPv4-embedded IPv6 packet is
       received and a route is found in the IPv4-embedded IPv6 routing
       table, the packet is forwarded to the IPv6 next-hop just like the
       handling for a normal IPv6 packet, without any translation.

   The classification of IPv4-embedded IPv6 packet is according to the
   IPv6 prefix of the destination address, which is either the Well
   Known Prefix (i.e., 64:ff9b::/96) or locally allocated as defined in
   [RFC6052].



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8.  Backdoor Connections

   In some deployments, IPv4 client networks are inter-connected across
   the IPv6 network, but also directly connected to each other.  The
   direct connections between IPv4 client networks, as sometimes called
   "backdoor" connections, can certainly be used to transport IPv4
   packets between IPv4 client networks.  In general, backdoor
   connections are preferred over the IPv6 network since there requires
   no address family translation.

9.  Prevention of Loops

   If an LSA sent from an AFXLBR into a client network could then be
   received by another AFXLBR, it would be possible for routing loops to
   occur.  To prevent loops, an AFXLBR MUST set the DN-bit [RFC4576] in
   any LSA that it sends to a client network.  The AFXLBR MUST also
   ignore any LSA received from a client network that already has the
   DN-bit sent.

10.  MTU Issues

   In the IPv6 network, there are no new MTU issues introduced by this
   document.  If a separate OSPFv3 instance (per [RFC5838]) is used for
   IPv4-embedded IPv6 routing, the MTU handling in the IPv6 network is
   the same as that of the default OSPFv3 instance.

   However, the MTU in the IPv6 network may be different than that of
   IPv4 client networks.  Since an IPv6 router will never fragment a
   packet, the packet size of any IPv4-embedded IPv6 packet entering the
   IPv6 network must be equal to or less than the MTU of the IPv6
   network.  In order to achieve this requirement, it is recommended
   that AFXLBRs perform IPv6 path discovery among themselves and the
   resulting MTU, after taking into account of the difference between
   the IPv4 header length and the IPv6 header length, must be
   "propagated" into IPv4 client networks, e.g., included in the OSPFv2
   Database Description packet.

   The details of passing the proper MTU into IPv4 client networks are
   beyond the scope of this document.

11.  Security Considerations

   There are several security aspects that require attention in the
   deployment practice described in this document.

   In the OSPFv3 transit network, the security considerations for OSPFv3
   are handled as usual, and in particular, authentication mechanisms
   described in [RFC6506] can be deployed.



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   When a separate OSPFv3 instance is used to support IPv4-embedded IPv6
   routing, the same Security Association (SA) (refer to [RFC4552] )
   MUST be used by the embedded IPv4 address instance as other instances
   utilizing the same link as specified in [RFC5838].

   Security considerations as documented in [RFC6052]  must also be
   thought through with proper implementation including the following:

   o  The IPv6 prefix that is used to carry an embedded IPv4 address
      (refer to Section 4.1) must be configured by the authorized
      operator on all participating AFXLBRs in a secure manner.  This is
      to help prevent an malicious attack resulting in network
      disruption, denial of service, and possible information
      disclosure.

   o  Effective mechanisms (such as reverse path checking) must be
      implemented in the IPv6 transit network (including AFXLIBR nodes)
      to prevent spoofing on embedded IPv4 addresses, which, otherwise,
      might be used as source addresses of malicious packets.

   o  If firewalls are used in IPv4 and/or IPv6 networks, the
      configuration on the routers must be consistent so there are no
      holes in the IPv4 address filtering.

   The details of security handling are beyond the scope of this
   document.

12.  Operational Considerations

   This document puts together some mechanisms based on existing
   technologies developed by IETF as an integrated solution to transport
   IPv4 packets over an IPv6 network using a separate OSPFv3 routing
   table.  There are several aspects that require attention for the
   deployment and operation.

   The tunnel-based solution documented in [RFC5565] and the solution
   proposed in this document are both used for transporting IPv4 packets
   over an IPv6 network, with different mechanisms.  The two methods are
   not related to each other, and they can co-exist in the same network
   if so deployed, without any conflict.

   If one approach is to be deployed, it is the operator's decision for
   the choice.  Note that each approach has its own characteristics and
   requirements.  E.g., the tunnel-based solution requires a mesh of
   inter-AFBR softwires (tunnels) spanning the IPv6 network, as well as
   iBGP to exchange routes between AFBRs ([RFC5565]); the approach in
   this document requires AFXLBR capable of performing IPv4-IPv6 packet
   header translation per [RFC6145].



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   To deploy the solution as documented here, there requires some
   configurations.  An IPv6 prefix must first be chosen that is used to
   form all the IPv4-embedded IPv6 addresses and prefixes advertised by
   AFXLBR in the IPv6 network; the detail is referred to Section 4.1.
   The IPv4-embedded IPv6 routing table is created by using a separate
   OSPFv3 instance in the IPv6 network, the configuration is
   accomplished according to [RFC5838], as described in Section 3.2.

   Note this document does not change any behavior of OSPFv3, and the
   existing or common practice should apply, in the context of
   scalability.  For example, the amount of routes that are advertised
   by OSPFv3 is one key concern.  With the solution as described in this
   document, IPv4-embedded IPv6 addresses and prefixes will be injected
   by AFXLBR into some part of the IPv6 network (see Section 3.1 for
   details), and a separate routing table will be used for IPv4-embedded
   IPv6 routing.  Care must be taken during the network design, such
   that 1) aggregation are performed on IPv4 addresses and prefixes
   before being advertised in the IPv6 network as described in
   Section 6, and 2) estimates are made as the amount of IPv4-embedded
   IPv6 routes that would be disseminated in the IPv6 network, and the
   size of the separate OSPFv3 routing table.

13.  IANA Considerations

   No new IANA assignments are required for this document.

14.  Acknowledgements

   Many thanks to Acee Lindem, Dan Wing, Joel Halpern, Mike Shand and
   Brian Carpenter for their comments.

15.  References

15.1.  Normative References

   [I-D.ietf-ospf-ospfv3-iid-registry-update]
              Retana, A. and D. Cheng, "OSPFv3 Instance ID Registry
              Update", draft-ietf-ospf-ospfv3-iid-registry-update-04
              (work in progress), April 2013.

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

   [RFC4576]  Rosen, E., Psenak, P., and P. Pillay-Esnault, "Using a
              Link State Advertisement (LSA) Options Bit to Prevent
              Looping in BGP/MPLS IP Virtual Private Networks (VPNs)",
              RFC 4576, June 2006.




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   [RFC5565]  Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh
              Framework", RFC 5565, June 2009.

   [RFC5838]  Lindem, A., Mirtorabi, S., Roy, A., Barnes, M., and R.
              Aggarwal, "Support of Address Families in OSPFv3", RFC
              5838, April 2010.

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, April 2011.

15.2.  Informative References

   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, June 2006.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, July 2008.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

   [RFC6506]  Bhatia, M., Manral, V., and A. Lindem, "Supporting
              Authentication Trailer for OSPFv3", RFC 6506, February
              2012.

Authors' Addresses

   Dean Cheng
   Huawei Technologies
   2330 Central Expressway
   Santa Clara, California  95050
   USA

   Email: dean.cheng@huawei.com


   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com








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   Alvaro Retana
   Cisco Systems
   7025 Kit Creek Rd.
   Research Triangle Park, North Carolina  27709
   USA

   Email: aretana@cisco.com












































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