[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75

Network Working Group                                    F. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Obsoletes: rfc6706 (if approved)                        January 03, 2014
Intended status: Standards Track
Expires: July 7, 2014


              Transmission of IPv6 Packets over AERO Links
                     draft-templin-aerolink-01.txt

Abstract

   This document specifies the operation of IPv6 over tunnel virtual
   Non-Broadcast, Multiple Access (NBMA) links using Automatic Extended
   Route Optimization (AERO).  Nodes attached to AERO links can exchange
   packets via trusted intermediate routers on the link that provide
   forwarding services to reach off-link destinations and/or redirection
   services to inform the node of an on-link neighbor that is closer to
   the final destination.  Operation of the IPv6 Neighbor Discovery (ND)
   protocol over AERO links is based on an IPv6 link local address
   format known as the AERO address.

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 July 7, 2014.

Copyright Notice

   Copyright (c) 2014 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



Templin                   Expires July 7, 2014                  [Page 1]


Internet-Draft                    AERO                      January 2014


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


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Asymmetric Extended Route Optimization (AERO)  . . . . . . . .  5
     3.1.  AERO Interface Characteristics . . . . . . . . . . . . . .  5
     3.2.  AERO Node Types  . . . . . . . . . . . . . . . . . . . . .  7
     3.3.  AERO Addresses . . . . . . . . . . . . . . . . . . . . . .  7
     3.4.  AERO Reference Operational Scenario  . . . . . . . . . . .  8
     3.5.  AERO Prefix Delegation and Router Discovery  . . . . . . . 10
       3.5.1.  AERO Client Behavior . . . . . . . . . . . . . . . . . 10
       3.5.2.  AERO Server Behavior . . . . . . . . . . . . . . . . . 11
     3.6.  AERO Redirection . . . . . . . . . . . . . . . . . . . . . 11
       3.6.1.  Classical Redirection Approaches . . . . . . . . . . . 11
       3.6.2.  AERO Redirection Concept of Operations . . . . . . . . 12
       3.6.3.  AERO Redirection Message Format  . . . . . . . . . . . 13
       3.6.4.  Sending Predirects . . . . . . . . . . . . . . . . . . 14
       3.6.5.  Processing Predirects and Sending Redirects  . . . . . 15
       3.6.6.  Re-encapsulating and Forwarding Redirects  . . . . . . 16
       3.6.7.  Processing Redirects . . . . . . . . . . . . . . . . . 17
       3.6.8.  Neighbor Reachability Considerations . . . . . . . . . 17
       3.6.9.  Mobility and Link-Layer Address Change
               Considerations . . . . . . . . . . . . . . . . . . . . 18
       3.6.10. Underlying Protocol Version Considerations . . . . . . 18
   4.  Implementation Status  . . . . . . . . . . . . . . . . . . . . 18
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 20
   Appendix A.  AERO Server and Relay Interworking  . . . . . . . . . 21
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23











Templin                   Expires July 7, 2014                  [Page 2]


Internet-Draft                    AERO                      January 2014


1.  Introduction

   This document specifies the operation of IPv6 over tunnel virtual
   Non-Broadcast, Multiple Access (NBMA) links using Automatic Extended
   Route Optimization (AERO).  Nodes attached to AERO links can exchange
   packets via trusted intermediate routers on the link that provide
   forwarding services to reach off-link destinations and/or redirection
   services to inform the node of an on-link neighbor that is closer to
   the final destination.

   Nodes on AERO links use an IPv6 link-local address format known as
   the AERO Address.  This address type has properties that statelessly
   link IPv6 Neighbor Discovery (ND) to IPv6 routing.  The AERO link can
   be used for tunneling to neighboring nodes on either IPv6 or IPv4
   networks, i.e., AERO views the IPv6 and IPv4 networks as equivalent
   links for tunneling.  The remainder of this document presents the
   AERO specification.


2.  Terminology

   The terminology in the normative references applies; the following
   terms are defined within the scope of this document:

   AERO link
      a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay
      configured over a node's attached IPv6 and/or IPv4 networks.  All
      nodes on the AERO link appear as single-hop neighbors from the
      perspective of IPv6.

   AERO interface
      a node's attachment to an AERO link.

   AERO address
      an IPv6 link-local address assigned to an AERO interface and
      constructed as specified in Section 3.3.

   AERO node
      a node that is connected to an AERO link and that participates in
      IPv6 Neighbor Discovery over the link.

   AERO Server ("server")
      a node that configures an advertising router interface on an AERO
      link over which it can provide default forwarding and redirection
      services for other AERO nodes.






Templin                   Expires July 7, 2014                  [Page 3]


Internet-Draft                    AERO                      January 2014


   AERO Client ("client")
      a node that configures a non-advertising router interface on an
      AERO link over which it can connect End User Networks (EUNs) to
      the AERO link.

   AERO Relay ("relay")
      a node that relays IPv6 packets between Servers on the same AERO
      link, and/or that forwards IPv6 packets between the AERO link and
      the IPv6 Internet.  An AERO Relay may or may not also be
      configured as an AERO Server.

   ingress tunnel endpoint (ITE)
      an AERO interface endpoint that injects packets into an AERO link.

   egress tunnel endpoint (ETE)
      an AERO interface endpoint that receives tunneled packets from an
      AERO link.

   underlying network
      a connected IPv6 or IPv4 network routing region over which AERO
      nodes tunnel IPv6 packets.

   underlying interface
      an AERO node's interface point of attachment to an underlying
      network.

   underlying address
      an IPv6 or IPv4 address assigned to an AERO node's underlying
      interface.  When UDP encapsulation is used, the UDP port number is
      also considered as part of the underlying address.  Underlying
      addresses are used as the source and destination addresses of the
      AERO encapsulation header.

   link-layer address
      the same as defined for "underlying address" above.

   network layer address
      an IPv6 address used as the source or destination address of the
      inner IPv6 packet header.

   end user network (EUN)
      an IPv6 network attached to a downstream interface of an AERO
      Client (where the AERO interface is seen as the upstream
      interface).

   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].



Templin                   Expires July 7, 2014                  [Page 4]


Internet-Draft                    AERO                      January 2014


3.  Asymmetric Extended Route Optimization (AERO)

   The following sections specify the operation of IPv6 over Automatic
   Extended Route Optimization (AERO) links:

3.1.  AERO Interface Characteristics

   All nodes connected to an AERO link configure their AERO interfaces
   as router interfaces (not host interfaces).  End system applications
   therefore do not bind directly to the AERO interface, but rather bind
   to end user network (EUN) interfaces beyond which their packets may
   be forwarded over an AERO interface.

   AERO interfaces use IPv6-in-IPv6 encapsulation [RFC2473] to exchange
   tunneled packets with AERO neighbors attached to an underlying IPv6
   network, and use IPv6-in-IPv4 encapsulation [RFC4213] to exchange
   tunneled packets with AERO neighbors attached to an underlying IPv4
   network.  AERO interfaces can also use IPsec encapsulation [RFC4301]
   (either IPv6-in-IPv6 or IPv6-in-IPv4) in environments where strong
   authentication and confidentiality are required.

   AERO interfaces further use the Subnetwork Encapsulation and
   Adaptation Layer (SEAL) [I-D.templin-intarea-seal] and can therefore
   configure an unlimited Maximum Transmission Unit (MTU).  This entails
   the insertion of a SEAL header (i.e., an IPv6 fragment header with
   the S bit set to 1) between the inner IPv6 header and the outer IP
   encapsulation header.  When NAT traversal and/or filtering middlebox
   traversal is necessary, a UDP header is further inserted between the
   outer IP encapsulation header and the SEAL header.  (Note that while
   [RFC6980] forbids fragmentation of IPv6 ND messages, the SEAL
   fragmentation header applies only to the outer tunnel encapsulation
   and not the inner IPv6 ND packet.)

   AERO interfaces maintain a neighbor cache and use an adaptation of
   standard unicast IPv6 ND messaging in which Router Solicitation (RS),
   Router Advertisement (RA), Neighbor Solicitation (NS) and Neighbor
   Advertisement (NA) messages do not include Source/Target Link Layer
   Address Options (S/TLLAO).  Instead, AERO nodes determine the link-
   layer addresses of neighbors by examining the encapsulation source
   address of any RS/RA/NS/NA messages they receive and ignore any
   S/TLLAOs included in these messages.  This is vital to the operation
   of AERO in environments in which AERO neighbors are separated by
   Network Address Translators (NATs) - either IPv4 or IPv6.

   AERO Redirect messages include a TLLAO the same as for any IPv6 link.
   The TLLAO includes the link-layer address of the target node,
   including both the IP address and the UDP source port number used by
   the target when it sends UDP-encapsulated packets over the AERO



Templin                   Expires July 7, 2014                  [Page 5]


Internet-Draft                    AERO                      January 2014


   interface (the TLLAO instead encodes the value 0 when the target does
   not use UDP encapsulation).  TLLAOs for target nodes that use an IPv6
   underlying address include the full 16 bytes of the IPv6 address as
   shown in Figure 1, while TLLAOs for target nodes that use an IPv4
   underlying address include only the 4 bytes of the IPv4 address as
   shown in Figure 2.

        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 = 2   |   Length = 3  |     UDP Source Port (or 0)    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Reserved                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +--                                                           --+
       |                                                               |
       +--                       IPv6 Address                        --+
       |                                                               |
       +--                                                           --+
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 1: AERO TLLAO Format for IPv6

        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 = 2   |   Length = 1  |     UDP Source Port (or 0)    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         IPv4 Address                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 2: AERO TLLAO  Format for IPv4

   Finally, nodes on AERO interfaces use a simple data origin
   authentication for encapsulated packets they receive from other
   nodes.  In particular, AERO Clients accept encapsulated packets with
   a link-layer source address belonging to their current AERO Server.
   AERO nodes also accept encapsulated packets with a link-layer source
   address that is correct for the network-layer source address.  The
   AERO node considers the link-layer source address correct for the
   network-layer source address if there is an IPv6 route that matches
   the network-layer source address as well as a neighbor cache entry
   corresponding to the next hop that includes the link-layer address.




Templin                   Expires July 7, 2014                  [Page 6]


Internet-Draft                    AERO                      January 2014


3.2.  AERO Node Types

   AERO Servers configure their AERO link interfaces as advertising
   router interfaces (see [RFC4861], Section 6.2.2) and may therefore
   send Router Advertisement (RA) messages that include non-zero Router
   Lifetimes.

   AERO Clients configure their AERO link interfaces as non-advertising
   router interfaces, i.e., even if the AERO Client otherwise displays
   the outward characteristics of an ordinary host (for example, the
   Client may internally configure both an AERO interface and (virtual)
   EUN interfaces).  AERO Clients are provisioned with IPv6 Prefix
   Delegations either through a DHCPv6 Prefix Delegation exchange with
   an AERO Server over the AERO link or via a static delegation obtained
   through an out-of-band exchange with an AERO link prefix delegation
   authority.

   AERO Relays relay packets between Servers connected to the same AERO
   link and also forward packets between the AERO link and the native
   IPv6 network.  The relaying process entails re-encapsulation of IPv6
   packets that were received from a first AERO Server and are to be
   forwarded without modification to a second AERO Server.

3.3.  AERO Addresses

   An AERO address is an IPv6 link-local address assigned to an AERO
   interface and with a 64-bit IPv6 prefix embedded within the interface
   identifier.  The AERO address is formatted as:

      fe80::[64-bit IPv6 prefix]

   Each AERO Client configures an AERO address based on the delegated
   prefix it has received from the AERO link prefix delegation
   authority.  The address begins with the prefix fe80::/64 and includes
   in its interface identifier the base /64 prefix taken from the
   Client's delegated IPv6 prefix.  The base prefix is determined by
   masking the delegated prefix with the prefix length.  For example, if
   an AERO Client has received the prefix delegation:

      2001:db8:1000:2000::/56

   it would construct its AERO address as:

      fe80::2001:db8:1000:2000

   An AERO Client may receive multiple IPv6 prefix delegations, in which
   case it would configure multiple AERO addresses - one for each
   delegated prefix.



Templin                   Expires July 7, 2014                  [Page 7]


Internet-Draft                    AERO                      January 2014


   Each AERO Server configures the special AERO address fe80::1 to
   support the operation of IPv6 Neighbor Discovery over the AERO link;
   the address therefore has the properties of an IPv6 Anycast address.
   While all Servers configure the same AERO address and therefore
   cannot be distinguished from one another at the network layer,
   Clients can still distinguish Servers at the link layer by examining
   the Servers' link-layer addresses.

   Nodes that are configured as pure AERO Relays (i.e., and that do not
   also act as Servers) do not configure an IPv6 address of any kind on
   their AERO interfaces.  The Relay's AERO interface is therefore used
   purely for transit and does not participate in IPv6 ND message
   exchanges.

3.4.  AERO Reference Operational Scenario

   Figure 3 depicts the AERO reference operational scenario.  The figure
   shows an AERO Server('A'), two AERO Clients ('B', 'D') and three
   ordinary IPv6 hosts ('C', 'E', 'F'):
































Templin                   Expires July 7, 2014                  [Page 8]


Internet-Draft                    AERO                      January 2014


                    .-(::::::::)
                 .-(::: IPv6 :::)-.   +-------------+
                (:::: Internet ::::)--|    Host F   |
                 `-(::::::::::::)-'   +-------------+
                    `-(::::::)-'       2001:db8:3::1
                         |
                  +--------------+
                  | AERO Server A|
                  | (C->B; E->D) |
                  +--------------+
                      fe80::1
                       L2(A)
                         |
       X-----+-----------+-----------+--------X
             |       AERO Link       |
            L2(B)                  L2(D)
     fe80::2001:db8:0:0      fe80::2001:db8:1:0         .-.
     +--------------+         +--------------+       ,-(  _)-.
     | AERO Client B|         | AERO Client D|    .-(_ IPv6  )-.
     | (default->A) |         | (default->A) |--(__    EUN      )
     +--------------+         +--------------+     `-(______)-'
     2001:DB8:0::/48           2001:DB8:1::/48           |
             |                                     2001:db8:1::1
            .-.                                   +-------------+
         ,-(  _)-.      2001:db8:0::1             |    Host E   |
      .-(_ IPv6  )-.   +-------------+            +-------------+
    (__    EUN      )--|    Host C   |
       `-(______)-'    +-------------+

               Figure 3: AERO Reference Operational Scenario

   In Figure 3, AERO Server ('A') connects to the AERO link and connects
   to the IPv6 Internet, either directly or via other IPv6 routers (not
   shown).  Server ('A') assigns the address fe80::1 to its AERO
   interface with link-layer address L2(A).  Server ('A') next arranges
   to add L2(A) to a published list of valid Servers for the AERO link.

   AERO Client ('B') assigns the address fe80::2001:db8:0:0 to its AERO
   interface with link-layer address L2(B).  Client ('B') configures a
   default route via the AERO interface with next-hop network-layer
   address fe80::1 and link-layer address L2(A), then sub-delegates the
   prefix 2001:db8:0::/48 to its attached EUNs.  IPv6 host ('C')
   connects to the EUN, and configures the network-layer address 2001:
   db8:0::1.

   AERO Client ('D') assigns the address fe80::2001:db8:1:0 to its AERO
   interface with link-layer address L2(D).  Client ('D') configures a
   default route via the AERO interface with next-hop network-layer



Templin                   Expires July 7, 2014                  [Page 9]


Internet-Draft                    AERO                      January 2014


   address fe80::1 and link-layer address L2(A), then sub-delegates the
   network-layer prefix 2001:db8:1::/48 to its attached EUNs.  IPv6 host
   ('E') connects to the EUN, and configures the network-layer address
   2001:db8:1::1.

   Finally, IPv6 host ('F') connects to an IPv6 network outside of the
   AERO link domain.  Host ('F') configures its IPv6 interface in a
   manner specific to its attached IPv6 link, and assigns the network-
   layer address 2001:db8:3::1 to its IPv6 link interface.

3.5.  AERO Prefix Delegation and Router Discovery

3.5.1.  AERO Client Behavior

   AERO Clients observe the IPv6 router requirements defined in
   [RFC6434] except that they act as "hosts" on their AERO interfaces
   for the purpose of prefix delegation and router discovery in the same
   fashion as for IPv6 Customer Premises Equipment (CPE) routers
   [RFC6204].  AERO Clients first discover the link-layer address of an
   AERO Server via static configuration, or through an automated means
   such as DNS name resolution.  In the absence of other information,
   the Client resolves the name "linkupnetworks.[domainname]", where
   [domainname] is the DNS domain appropriate for the Client's attached
   underlying network.

   After discovering the link-layer address, the Client then acts as a
   requesting router to obtain IPv6 prefixes through DHCPv6 Prefix
   Delegation [RFC3633] via the Server.  (The Client can also obtain
   prefixes through out-of-band means such as static administrative
   configuration, etc.).  After the Client acquires prefixes, it sub-
   delegates them to nodes and links within its attached EUNs.  It also
   assigns the link-local AERO address(es) taken from its delegated
   prefix(es) to the AERO interface (see: Section 3.3).

   After acquiring prefixes, the Client next prepares a unicast IPv6
   Router Solicitation (RS) message using its AERO address as the
   network-layer source address and fe80::1 as the network-layer
   destination address.  The Client then tunnels the packet to the
   Server using one of its underlying addresses as the link-layer source
   address and using an underlying address of the Server as the link-
   layer destination address.  The Server in turn returns a unicast
   Router Advertisement (RA) message, which the Client uses to create an
   IPv6 neighbor cache entry for the Server on the AERO interface per
   [RFC4861].  The link-layer address for the neighbor cache entry is
   taken from the link-layer source address of the RA message.

   After obtaining prefixes and performing an initial RS/RA exchange
   with a Server, the Client continues to send periodic RS messages to



Templin                   Expires July 7, 2014                 [Page 10]


Internet-Draft                    AERO                      January 2014


   the server to obtain new RAs in order to keep neighbor cache entries
   alive.  The Client can also forward IPv6 packets destined to networks
   beyond its local EUNs via the Server as an IPv6 default router.  The
   Server may in turn return a Redirect message informing the Client of
   a neighbor on the AERO link that is topologically closer to the final
   destination as specified in Section 3.6.

3.5.2.  AERO Server Behavior

   AERO Servers observe the IPv6 router requirements defined in
   [RFC6434].  They further configure a DHCPv6 relay/server function on
   their AERO links and/or provide an administrative interface for
   delegation of network-layer addresses and prefixes.  When the Server
   delegates prefixes, it also establishes forwarding table entries that
   list the AERO address of the Client as the next hop toward the
   delegated IPv6 prefixes (where the AERO address is constructed as
   specified in Section 3.3).

   Servers respond to RS messages from Clients on their advertising AERO
   interfaces by returning an RA message.  When the Server receives an
   RS message, it creates or updates a neighbor cache entry using the
   network layer source address as the neighbor's network layer address
   and using the link-layer source address of the RS message as the
   neighbor's link-layer address.

   When the Server forwards a packet via the same AERO interface on
   which it arrived, it initiates an AERO route optimization procedure
   as specified in Section 3.6.

3.6.  AERO Redirection

   Section 3.4 describes the AERO reference operational scenario.  We
   now discuss the operation and protocol details of AERO Redirection
   with respect to this reference scenario.

3.6.1.  Classical Redirection Approaches

   With reference to Figure 3, when the IPv6 source host ('C') sends a
   packet to an IPv6 destination host ('E'), the packet is first
   forwarded via the EUN to AERO Client ('B').  Client ('B') then
   forwards the packet over its AERO interface to AERO Server ('A'),
   which then forwards the packet to AERO Client ('D'), where the packet
   is finally forwarded to the IPv6 destination host ('E').  When Server
   ('A') forwards the packet back out on its advertising AERO interface,
   it must arrange to redirect Client ('B') toward Client ('D') as a
   better next-hop node on the AERO link that is closer to the final
   destination.  However, this redirection process applied to AERO
   interfaces must be more carefully orchestrated than on ordinary links



Templin                   Expires July 7, 2014                 [Page 11]


Internet-Draft                    AERO                      January 2014


   since the parties may be separated by potentially many underlying
   network routing hops.

   Consider a first alternative in which Server ('A') informs Client
   ('B') only and does not inform Client ('D') (i.e., "classical
   redirection").  In that case, Client ('D') has no way of knowing that
   Client ('B') is authorized to forward packets from their claimed
   network-layer source addresses, and it may simply elect to drop the
   packets.  Also, Client ('B') has no way of knowing whether Client
   ('D') is performing some form of source address filtering that would
   reject packets arriving from a node other than a trusted default
   router, nor whether Client ('D') is even reachable via a direct path
   that does not involve Server ('A').

   Consider a second alternative in which Server ('A') informs both
   Client ('B') and Client ('D') separately, via independent redirection
   control messages (i.e., "augmented redirection").  In that case, if
   Client ('B') receives the redirection control message but Client
   ('D') does not, subsequent packets sent by Client ('B') could be
   dropped due to filtering since Client ('D') would not have a route to
   verify their source network-layer addresses.  Also, if Client ('D')
   receives the redirection control message but Client ('B') does not,
   subsequent packets sent in the reverse direction by Client ('D')
   would be lost.

   Since both of these alternatives have shortcomings, a new redirection
   technique (i.e., "AERO redirection") is needed.

3.6.2.  AERO Redirection Concept of Operations

   Again, with reference to Figure 3, when source host ('C') sends a
   packet to destination host ('E'), the packet is first forwarded over
   the source host's attached EUN to Client ('B'), which then forwards
   the packet via its AERO interface to Server ('A').

   Using AERO redirection, Server ('A') then forwards the packet out the
   same AERO interface toward Client ('D') and also sends an AERO
   "Predirect" message forward to Client ('D') as specified in
   Section 3.6.4.  The Predirect message includes Client ('B')'s
   network- and link-layer addresses as well as information that Client
   ('D') can use to determine the IPv6 prefix used by Client ('B') .
   After Client ('D') receives the Predirect message, it process the
   message and returns an AERO Redirect message destined for Client
   ("B") via Server ('A') as specified in Section 3.6.5.  During the
   process, Client ('D') also creates or updates a neighbor cache entry
   for Client ('B'), and creates an IPv6 route for Client ('B')'s IPv6
   prefix.




Templin                   Expires July 7, 2014                 [Page 12]


Internet-Draft                    AERO                      January 2014


   When Server ('A') receives the Redirect message, it processes the
   message and forwards it on to Client ('B') as specified in
   Section 3.6.6.  The message includes Client ('D')'s network- and
   link-layer addresses as well as information that Client ('B') can use
   to determine the IPv6 prefix used by Client ('D').  After Client
   ('B') receives the Redirect message, it processes the message as
   specified in Section 3.6.7.  During the process, Client ('B') also
   creates or updates a neighbor cache entry for Client ('D'), and
   creates an IPv6 route for Client ('D')'s IPv6 prefix.

   Following the above Predirect/Redirect message exchange, forwarding
   of packets from Client ('B') to Client ('D') without involving Server
   ('A) as an intermediary is enabled.  The mechanisms that support this
   exchange are specified in the following sections.

3.6.3.  AERO Redirection Message Format

   AERO Redirect/Predirect messages use the same format as for ICMPv6
   Redirect messages depicted in Section 4.5 of [RFC4861], but also
   include a new field (the "Prefix Length" field) taken from the
   Redirect message Reserved field.  The Redirect/Predirect messages are
   formatted as shown in Figure 4:





























Templin                   Expires July 7, 2014                 [Page 13]


Internet-Draft                    AERO                      January 2014


    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 (=137)  |  Code (=0/1)  |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Prefix Length |                 Reserved                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Target Address                          +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                     Destination Address                       +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Options ...
   +-+-+-+-+-+-+-+-+-+-+-+-

             Figure 4: AERO Redirect/Predirect Message Format

3.6.4.  Sending Predirects

   When an AERO Server forwards a packet out the same AERO interface
   that it arrived on, the Server sends a Predirect message forward
   toward the AERO Client nearest the destination instead of sending a
   Redirect message back to AERO Client nearest the source.

   In the reference operational scenario, when Server ('A') forwards a
   packet sent by Client ('B') toward Client ('D'), it also sends a
   Predirect message forward toward Client ('D'), subject to rate
   limiting (see Section 8.2 of [RFC4861]).  Server ('A') prepares the
   Predirect message as follows:

   o  the link-layer source address is set to 'L2(A)' (i.e., the
      underlying address of Server ('A')).

   o  the link-layer destination address is set to 'L2(D)' (i.e., the
      underlying address of Client ('D')).





Templin                   Expires July 7, 2014                 [Page 14]


Internet-Draft                    AERO                      January 2014


   o  the network-layer source address is set to fe80::1 (i.e., the AERO
      address of Server ('A')).

   o  the network-layer destination address is set to fe80::2001:db8:1:0
      (i.e., the AERO address of Client ('D')).

   o  the Type is set to 137.

   o  the Code is set to 1 to indicate "Predirect".

   o  the Prefix Length is set to the length of the prefix to be applied
      to Target address.

   o  the Target Address is set to fe80::2001:db8:0::0 (i.e., the AERO
      address of Client ('B')).

   o  the Destination Address is set to the IPv6 source address of the
      packet that triggered the Predirection event.

   o  the message includes a TLLAO set to 'L2(B)' (i.e., the underlying
      address of Client ('B')).

   o  the message includes a Redirected Header Option (RHO) that
      contains the originating packet truncated to ensure that at least
      the network-layer header is included but the size of the message
      does not exceed 1280 bytes.

   Server ('A') then sends the message forward to Client ('D').

3.6.5.  Processing Predirects and Sending Redirects

   When Client ('D') receives a Predirect message, it accepts the
   message only if it has a link-layer source address of the Server,
   i.e.  'L2(A)'.  Client ('D') further accepts the message only if it
   is willing to serve as a redirection target.  Next, Client ('D')
   validates the message according to the ICMPv6 Redirect message
   validation rules in Section 8.1 of [RFC4861].

   In the reference operational scenario, when the Client ('D') receives
   a valid Predirect message, it either creates or updates a neighbor
   cache entry that stores the Target Address of the message as the
   network-layer address of Client ('B') and stores the link-layer
   address found in the TLLAO as the link-layer address of Client ('B').
   Client ('D') then applies the Prefix Length to the Interface
   Identifier portion of the Target Address and records the resulting
   IPv6 prefix in its IPv6 forwarding table.

   After processing the message, Client ('D') prepares a Redirect



Templin                   Expires July 7, 2014                 [Page 15]


Internet-Draft                    AERO                      January 2014


   message response as follows:

   o  the link-layer source address is set to 'L2(D)' (i.e., the link-
      layer address of Client ('D')).

   o  the link-layer destination address is set to 'L2(A)' (i.e., the
      link-layer address of Server ('A')).

   o  the network-layer source address is set to 'L3(D)' (i.e., the AERO
      address of Client ('D')).

   o  the network-layer destination address is set to 'L3(B)' (i.e., the
      AERO address of Client ('B')).

   o  the Type is set to 137.

   o  the Code is set to 0 to indicate "Redirect".

   o  the Prefix Length is set to the length of the prefix to be applied
      to the Target and Destination address.

   o  the Target Address is set to fe80::2001:db8:1::1 (i.e., the AERO
      address of Client ('D')).

   o  the Destination Address is set to the IPv6 destination address of
      the packet that triggered the Redirection event.

   o  the message includes a TLLAO set to 'L2(D)' (i.e., the underlying
      address of Client ('D')).

   o  the message includes as much of the RHO copied from the
      corresponding AERO Predirect message as possible such that at
      least the network-layer header is included but the size of the
      message does not exceed 1280 bytes.

   After Client ('D') prepares the Redirect message, it sends the
   message to Server ('A').

3.6.6.  Re-encapsulating and Forwarding Redirects

   When Server ('A') receives a Redirect message, it accepts the message
   only if it has a neighbor cache entry that associates the message's
   link-layer source address with the network-layer source address.
   Next, Server ('A') validates the message according to the ICMPv6
   Redirect message validation rules in Section 8.1 of [RFC4861].
   Following validation, Server ('A') re-encapsulates the Redirect as
   discussed in [I-D.templin-intarea-seal], and then forwards a re-
   encapsulated Redirect on to Client ('B') as follows.



Templin                   Expires July 7, 2014                 [Page 16]


Internet-Draft                    AERO                      January 2014


   In the reference operational scenario, Server ('A') receives the
   Redirect message from Client ('D') and prepares to forward a
   corresponding Redirect message to Client ('B').  Server ('A') then
   verifies that Client ('D') is authorized to use the Prefix Length in
   the Redirect message when applied to the AERO address in the network-
   layer source of the Redirect message, and discards the message if
   verification fails.  Otherwise, Server ('A') re-encapsulates the
   redirect by changing the link-layer source address of the message to
   'L2(A)', changing the network-layer source address of the message to
   fe80::1, and changing the link-layer destination address to 'L2(B)' .
   Server ('A') finally forwards the re-encapsulated message to the
   ingress node ('B') without decrementing the network-layer IPv6 header
   Hop Limit field.

   While not shown in Figure 3, AERO Relays forward Redirect and
   Predirect messages in exactly this same fashion described above.  See
   Figure 5 in Appendix A for an extension of the reference operational
   scenario that includes Relays.

3.6.7.  Processing Redirects

   When Client ('B') receives the Redirect message, it accepts the
   message only if it has a link-layer source address of the Server,
   i.e.  'L2(A)'.  Next, Client ('B') validates the message according to
   the ICMPv6 Redirect message validation rules in Section 8.1 of
   [RFC4861].  Following validation, Client ('B') then processes the
   message as follows.

   In the reference operational scenario, when Client ('B') receives the
   Redirect message, it either creates or updates a neighbor cache entry
   that stores the Target Address of the message as the network-layer
   address of Client ('D') and stores the link-layer address found in
   the TLLAO as the link-layer address of Client ('D').  Client ('B')
   then applies the Prefix Length to the Interface Identifier portion of
   the Target Address and records the resulting IPv6 prefix in its IPv6
   forwarding table.

   Now, Client ('B') has an IPv6 forwarding table entry for
   Client('D')'s prefix, and Client ('D') has an IPv6 forwarding table
   entry for Client ('B')'s prefix.  Thereafter, the clients may
   exchange ordinary network-layer data packets directly without
   forwarding through Server ('A').

3.6.8.  Neighbor Reachability Considerations

   When Client ('B') receives a redirection message informing it of
   Client ('D') as a better next hop, there is a question in point as to
   whether Client ('D') can be reached directly without forwarding



Templin                   Expires July 7, 2014                 [Page 17]


Internet-Draft                    AERO                      January 2014


   through Server ('A').  On some AERO links, it may be reasonable for
   Client ('B') to (optimistically) assume that reachability is
   transitive, and to immediately begin forwarding data packets to
   Client ('D') without testing reachability.

   On AERO links in which an optimistic assumption of transitive
   reachability may be unreasonable, however, Client ('B') can continue
   to send packets via Server ('A') until it tests the direct path to
   Client ('D'), e.g., by sending an initial NS message to elicit an NA
   response.  The Clients thereafter follow the Neighbor Unreachability
   Detection (NUD) procedures in Section 7.3 of [RFC4861], and can
   resume sending packets via Server ('A') at any time the direct path
   appears to be failing.

   If Client ('B') is unable to elicit an NA response from Client ('D')
   after MAX_RETRY attempts, it should consider the direct path to be
   unusable for forwarding purposes but still viable for ingress
   filtering purposes.

   If a direct path between the Clients can be established, they can
   thereafter process any link-layer errors as a hint that the direct
   path has either failed or has become intermittent.

3.6.9.  Mobility and Link-Layer Address Change Considerations

   When Client ('B') needs to change its link-layer address (e.g., due
   to a mobility event, due to a change in underlying network interface,
   etc.), it sends an immediate NS message forward to Client ('D'),
   which then discovers the new link-layer address.

   If both Client ('B') and Client ('D') change their link-layer
   addresses simultaneously, the NS/NA exchanges between the two
   neighbors may fail.  In that case, the Clients follow the same
   neighbor unreachability procedures specified in Section 3.7.9.

3.6.10.  Underlying Protocol Version Considerations

   Again with reference to Figure 3, Client ('B') may connect only to an
   IPvX underlying network, while Client ('D') connects only to an IPvY
   underlying network.  In that case, Client ('B') has no means for
   reaching Client ('D') directly (since they connect to underlying
   networks of different IP protocol versions) and so must ignore any
   Redirects and continue to send packets via Server ('A').


4.  Implementation Status

   An early implementation is available at:



Templin                   Expires July 7, 2014                 [Page 18]


Internet-Draft                    AERO                      January 2014


   http://linkupnetworks.com/seal/sealv2-1.0.tgz.


5.  IANA Considerations

   There are no IANA actions required for this document.


6.  Security Considerations

   AERO link security considerations are the same as for standard IPv6
   Neighbor Discovery [RFC4861] except that AERO improves on some
   aspects.  In particular, AERO is dependent on a trust basis between
   AERO Clients and Servers, where the Clients only engage in the AERO
   mechanism when it is facilitated by a trusted Server.

   AERO links must be protected against link-layer address spoofing
   attacks in which an attacker on the link pretends to be a trusted
   neighbor.  Links that provide link-layer securing mechanisms (e.g.,
   WiFi networks) and links that provide physical security (e.g.,
   enterprise network LANs) provide a first line of defense that is
   often sufficient.  In other instances, securing mechanisms such as
   Secure Neighbor Discovery (SeND) [RFC3971] or IPsec [RFC4301] must be
   used.


7.  Acknowledgements

   Discussions both on the v6ops list and in private exchanges helped
   shape some of the concepts in this work.  Individuals who contributed
   insights include Mikael Abrahamsson, Fred Baker, Stewart Bryant,
   Brian Carpenter, Brian Haberman, Joel Halpern, and Lee Howard.
   Members of the IESG also provided valuable input during their review
   process that greatly improved the document.  Special thanks go to
   Stewart Bryant, Joel Halpern and Brian Haberman for their shepherding
   guidance.

   This work has further been encouraged and supported by Boeing
   colleagues including Balaguruna Chidambaram, Jeff Holland, Cam
   Brodie, Yueli Yang, Wen Fang, Ed King, Mike Slane, Kent Shuey, Gen
   MacLean, and other members of the BR&T and BIT mobile networking
   teams.

   Earlier works on NBMA tunneling approaches are found in
   [RFC2529][RFC5214][RFC5569].


8.  References



Templin                   Expires July 7, 2014                 [Page 19]


Internet-Draft                    AERO                      January 2014


8.1.  Normative References

   [I-D.templin-intarea-seal]
              Templin, F., "The Subnetwork Encapsulation and Adaptation
              Layer (SEAL)", draft-templin-intarea-seal-65 (work in
              progress), October 2013.

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, September 1981.

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

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213, October 2005.

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

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC6434]  Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
              Requirements", RFC 6434, December 2011.

8.2.  Informative References

   [IRON]     Templin, F., "The Internet Routing Overlay Network
              (IRON)", Work in Progress, June 2012.

   [RFC2529]  Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
              Domains without Explicit Tunnels", RFC 2529, March 1999.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for



Templin                   Expires July 7, 2014                 [Page 20]


Internet-Draft                    AERO                      January 2014


              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC5214]  Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
              Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
              March 2008.

   [RFC5569]  Despres, R., "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd)", RFC 5569, January 2010.

   [RFC6204]  Singh, H., Beebee, W., Donley, C., Stark, B., and O.
              Troan, "Basic Requirements for IPv6 Customer Edge
              Routers", RFC 6204, April 2011.

   [RFC6980]  Gont, F., "Security Implications of IPv6 Fragmentation
              with IPv6 Neighbor Discovery", RFC 6980, August 2013.


Appendix A.  AERO Server and Relay Interworking

   Figure 3 depicts a reference AERO operational scenario with a single
   Server on the AERO link.  In order to support scaling to larger
   numbers of nodes, the AERO link can deploy multiple Servers and
   Relays, e.g., as shown in Figure 5.


















Templin                   Expires July 7, 2014                 [Page 21]


Internet-Draft                    AERO                      January 2014


                             .-(::::::::)
                          .-(::: IPv6 :::)-.
                         (:: Internetwork ::)
                          `-(::::::::::::)-'
                             `-(::::::)-'
                                  |
       +--------------+    +------+-------+    +--------------+
       |AERO Server C |    | AERO Relay D |    |AERO Server E |
       | (default->D) |    | (A->C; G->E) |    | (default->D) |
       |    (A->B)    |    +-------+------+    |    (G->F)    |
       +-------+------+            |           +------+-------+
               |                   |                  |
       X---+---+-------------------+------------------+---+---X
           |                  AERO Link                   |
     +-----+--------+                            +--------+-----+
     |AERO Client B |                            |AERO Client F |
     | (default->C) |                            | (default->E) |
     +--------------+                            +--------------+
           .-.                                         .-.
        ,-(  _)-.                                   ,-(  _)-.
     .-(_ IPv6  )-.                              .-(_ IPv6  )-.
    (__    EUN      )                           (__    EUN      )
       `-(______)-'                                `-(______)-'
            |                                           |
        +--------+                                  +--------+
        | Host A |                                  | Host G |
        +--------+                                  +--------+

                 Figure 5: AERO Server/Relay Interworking

   In this example, AERO Client ('B') associates with AERO Server ('C'),
   while AERO Client ('F') associates with AERO Server ('E').
   Furthermore, AERO Servers ('C') and ('E') do not associate with each
   other directly, but rather have an association with AERO Relay ('D')
   (i.e., a router that has full topology information concerning its
   associated Servers and their Clients).  Relay ('D') connects to the
   AERO link, and also connects to the native IPv6 Internetwork.

   When host ('A') sends a packet toward destination host ('G'), IPv6
   forwarding directs the packet through the EUN to Client ('B'), which
   forwards the packet to Server ('C') in absence of more-specific
   forwarding information.  Server ('C') forwards the packet, and it
   also generates an AERO Predirect message that is then forwarded
   through Relay ('D') to Server ('E').  When Server ('E') receives the
   message, it forwards the message to Client ('F').

   After processing the AERO Predirect message, Client ('F') sends an
   AERO Redirect message to Server ('E').  Server ('E'), in turn,



Templin                   Expires July 7, 2014                 [Page 22]


Internet-Draft                    AERO                      January 2014


   forwards the message through Relay ('D') to Server ('C').  When
   Server ('C') receives the message, it forwards the message to Client
   ('B') informing it that host 'G's EUN can be reached via Client
   ('F'), thus completing the AERO redirection.

   The network layer routing information shared between Servers and
   Relays must be carefully coordinated in a manner outside the scope of
   this document.  In particular, Relays require full topology
   information, while individual Servers only require partial topology
   information (i.e., they only need to know the EUN prefixes associated
   with their current set of Clients).  See [IRON] for an architectural
   discussion of routing coordination between Relays and Servers.


Author's Address

   Fred L. Templin (editor)
   Boeing Research & Technology
   P.O. Box 3707
   Seattle, WA  98124
   USA

   Email: fltemplin@acm.org




























Templin                   Expires July 7, 2014                 [Page 23]


Html markup produced by rfcmarkup 1.122, available from https://tools.ietf.org/tools/rfcmarkup/