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INTERNET-DRAFT                                                T. Herbert
Intended Status: Standard                                     Quantonium
Expires: July 2019                                         Vikram Siwach
                                                  Independent consultant

                                                        January 28, 2019


                         Address Mapping System
                      draft-herbert-intarea-ams-00


Abstract

   This document describes the Address Mapping System that is a generic,
   extensible, and scalable system for mapping network addresses to
   other network addresses. The Address Mapping System is intended to be
   used in conjunction with overlay techniques which facilitate
   transmission of packets across overlay networks. Information returned
   by the Address Mapping System can include the particular network
   overlay method and instructions related to the method.  The Address
   Mapping System has a number of potential use cases networking
   including identifier-locator protocols, network virtualization, and
   promotion of privacy.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts.

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   http://www.ietf.org/1id-abstracts.html

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   http://www.ietf.org/shadow.html


Copyright and License Notice



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   Copyright (c) 2019 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
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   publication of this document. Please review these documents
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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  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1 Use cases  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.3 Terminology  . . . . . . . . . . . . . . . . . . . . . . . .  7
   2  Architecture  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     2.1  Reference topology  . . . . . . . . . . . . . . . . . . . . 10
     2.2 Functional components  . . . . . . . . . . . . . . . . . . . 10
     2.3 AMS router (AMS-R) . . . . . . . . . . . . . . . . . . . . . 10
       2.3.1 AMS router operation . . . . . . . . . . . . . . . . . . 11
     2.4 AMS forwarder (AMS-F)  . . . . . . . . . . . . . . . . . . . 11
       2.4.1 Overlay termination  . . . . . . . . . . . . . . . . . . 12
       2.4.2 Overlay forwarding . . . . . . . . . . . . . . . . . . . 12
   3  Address Mapping Router Protocol (AMRP)  . . . . . . . . . . . . 13
     3.1 Key/value database . . . . . . . . . . . . . . . . . . . . . 13
     3.2 BGP  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     3.3 3GPP uses GTP  . . . . . . . . . . . . . . . . . . . . . . . 13
   4   Address Mapping Forwarder Protocol (AMFP)  . . . . . . . . . . 13
     4.1 Common header format . . . . . . . . . . . . . . . . . . . . 14
     4.2 Hello messages . . . . . . . . . . . . . . . . . . . . . . . 16
     4.3 Hello Message TLVs . . . . . . . . . . . . . . . . . . . . . 15
     4.2 Hello messages . . . . . . . . . . . . . . . . . . . . . . . 16
       4.1.1 TLV format . . . . . . . . . . . . . . . . . . . . . . . 17
       4.1.2 TLV types  . . . . . . . . . . . . . . . . . . . . . . . 17
       4.1.3 Default overlay method . . . . . . . . . . . . . . . . . 17
       4.1.4 Default timeout  . . . . . . . . . . . . . . . . . . . . 18
       4.1.5 Default priority . . . . . . . . . . . . . . . . . . . . 18
       4.1.6 Default weight . . . . . . . . . . . . . . . . . . . . . 19
       4.1.6 Default instructions . . . . . . . . . . . . . . . . . . 19
       4.1.5 Supported overlay methods  . . . . . . . . . . . . . . . 20
     4.4  AMFP Version 0  . . . . . . . . . . . . . . . . . . . . . . 20
       4.4.1 Map request  . . . . . . . . . . . . . . . . . . . . . . 20
       4.4.2 Map information  . . . . . . . . . . . . . . . . . . . . 21



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       4.4.3 Compressed map information . . . . . . . . . . . . . . . 24
       4.4.4 Locator unreachable  . . . . . . . . . . . . . . . . . . 26
       4.4.5 Identifier and locator types . . . . . . . . . . . . . . 26
     4.5  Operation . . . . . . . . . . . . . . . . . . . . . . . . . 27
       4.5.1 Version negotiation  . . . . . . . . . . . . . . . . . . 27
       4.5.2 Populating an mapping cache  . . . . . . . . . . . . . . 27
       4.5.3 Redirects  . . . . . . . . . . . . . . . . . . . . . . . 28
         4.5.3.1 Proactive push with redirect . . . . . . . . . . . . 28
         4.5.3.2 Redirect rate limiting . . . . . . . . . . . . . . . 28
       4.5.4 Map request/reply  . . . . . . . . . . . . . . . . . . . 28
       4.5.5 Push mappings  . . . . . . . . . . . . . . . . . . . . . 29
       4.5.6 Cache maintenance  . . . . . . . . . . . . . . . . . . . 29
         4.5.6.1 Timeouts . . . . . . . . . . . . . . . . . . . . . . 29
         4.5.6.2 Cache refresh  . . . . . . . . . . . . . . . . . . . 30
       4.5.7 AMS forwarder processing . . . . . . . . . . . . . . . . 30
       4.5.8 Locator unreachable handling . . . . . . . . . . . . . . 30
       4.5.9 Control Connections  . . . . . . . . . . . . . . . . . . 31
       4.5.10 Protocol errors . . . . . . . . . . . . . . . . . . . . 31
   5  Stateless mapping optimization  . . . . . . . . . . . . . . . . 32
     5.1  Firewall and Service Tickets encoding . . . . . . . . . . . 32
     5.2  Address mapping encoding  . . . . . . . . . . . . . . . . . 32
     5.3 Reference topology . . . . . . . . . . . . . . . . . . . . . 33
     5.4  Operation . . . . . . . . . . . . . . . . . . . . . . . . . 34
       5.4.1 Ticket requests  . . . . . . . . . . . . . . . . . . . . 34
       5.4.2 Qualified locators . . . . . . . . . . . . . . . . . . . 34
         5.4.2.1 Fully qualified locators . . . . . . . . . . . . . . 35
         5.4.2.2 Unqualified locators . . . . . . . . . . . . . . . . 35
       5.4.3 AMS forwarder processing . . . . . . . . . . . . . . . . 35
       5.4.4 Transit to the peer  . . . . . . . . . . . . . . . . . . 35
       5.4.5 Ingress into the origin network  . . . . . . . . . . . . 36
       5.4.6 Overlay termination  . . . . . . . . . . . . . . . . . . 36
       5.4.7 Fallback . . . . . . . . . . . . . . . . . . . . . . . . 36
       5.4.8 Mobile events  . . . . . . . . . . . . . . . . . . . . . 36
       5.4.10 Interaction with expired tickets  . . . . . . . . . . . 37
   6  Privacy in Internet addresses . . . . . . . . . . . . . . . . . 37
     6.1 Criteria for privacy in addressing . . . . . . . . . . . . . 38
     6.2  Achieving strong privacy  . . . . . . . . . . . . . . . . . 38
     6.3 Scaling network state  . . . . . . . . . . . . . . . . . . . 39
       6.3.1 Hidden aggregation . . . . . . . . . . . . . . . . . . . 39
       6.3.2 Address format . . . . . . . . . . . . . . . . . . . . . 40
       6.3.3 Practicality of hidden aggregation methods . . . . . . . 40
     6.4 Scaling bulk address assignment  . . . . . . . . . . . . . . 41
   7  Address Mapping System in 5G networks . . . . . . . . . . . . . 42
     7.1 Architecture . . . . . . . . . . . . . . . . . . . . . . . . 42
     7.2 Protocol layering  . . . . . . . . . . . . . . . . . . . . . 43
     7.3 Control plane between AMS and network  . . . . . . . . . . . 44
     7.4 AMS and network slices . . . . . . . . . . . . . . . . . . . 44
     7.4 AMS in 4G networks . . . . . . . . . . . . . . . . . . . . . 45



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     7.5 Overlay forwarding . . . . . . . . . . . . . . . . . . . . . 45
   8  Security Considerations . . . . . . . . . . . . . . . . . . . . 46
   9  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 47
   10  References . . . . . . . . . . . . . . . . . . . . . . . . . . 47
     10.1  Normative References . . . . . . . . . . . . . . . . . . . 47
     10.2  Informative References . . . . . . . . . . . . . . . . . . 47
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 47












































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1  Introduction

   This document describes the Address Mapping System (AMS). AMS is a
   system that maps network addresses to other network addresses. The
   canonical use case is to map "identifiers" to "locators" (applying
   identifier-locator split terminology). Identifiers are logical
   addresses that identify a node, and locators are addresses that
   indicate the current location of a node. Identifiers are mapped to
   locators at points in the data path to facilitate device mobility or
   or network virtualization.

   The address mapping system may be queried on a per packet basis in
   the data path. For instance, an encapsulating tunnel ingress node for
   virtualization would perform a lookup on each destination virtual
   address to discover the address of the physical node to which a
   packet should be forwarded. It follows that access to the mapping
   system is expected to be tightly coupled with nodes that query the
   system to perform packet forwarding.

   The mapping system contains a database or table of all the address
   mappings for a mapping domain. The database may be distributed across
   some number of nodes, sharded for scalability, and caches may be used
   to optimize communications. The mappings in a mapping system may be
   very dynamic, for instance end user devices in a mobile network may
   change location within the network at a high rate (e.g. a mobile
   device in fast moving automobile may frequently connect to different
   cells). Protocols are defined to synchronize the mapping information
   across devices that participate in the address mapping system.

1.1 Use cases

   This section describes some of the use cases of the Address Mapping
   System.

      o Network virtualization

      o Identifier/locator protocols

      o Address resolution

      o Privacy in Internet addressing

      o Mobile networks

1.2 Requirements

   Requirements for the Internet Addressing Mapping system are:




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      o Allow use of different overlay protocols

        The mapping system should be agnostic to the protocol used to
        implement an underlying network overlay. An overlay could be
        implemented using an encapsulation protocol, such as GTP, GUE,
        LISP, VXLAN, etc., or using and identifier/locator address split
        protocol such as ILA. A network may simultaneously use different
        protocols per its needs. Mapping information provided by the
        address mapping system could include instructions that indicate
        the overlay protocol to be used when sending to a destination.

      o Secure access to mapping system

        An address mapping system may contain sensitive information,
        particularly in the case that locators would reveal location or
        identity of specific users. Access to the mapping system must be
        tightly controlled. Law enforcement considerations may require
        maintaining a history of mappings to provide under legal order.

      o Mapping caches (anchorless mobility)

        Mapping caches may be implemented at the network edge to perform
        overlay forwarding and avoid triangular routing through
        centralized anchor points. A cache may be implemented as a
        working set cache or could be pre-populated with mappings for
        common destinations. The purpose of the cache is to optimize
        communications for critical communications, however the use of
        caches should not be required for viable communications.

      o Scalability

        Address mapping systems should be able to scale to at least a
        billion mappings in a single mapping system domain. This
        accounts for a large number of devices, where each device may
        have some number of associated mappings. It follows that a large
        deployment will likely need a number of sharded mapping servers
        each of which may be replicated for reliability.

      o Resiliency against Denial of Service attack

        An address mapping system must be resistant to Denial of Service
        attacks. For instance, if a mapping cache is used then a
        resource exhaustion attack on a mapping cache must not result in
        loss of service to users.

      o User privacy

        An address mapping system must facilitate user privacy. As



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        mentioned above, the mapping system must be secured to prevent
        intrusion for sensitive personal information. The mapping system
        can also foster privacy in addressing by supporting untrackable,
        per-flow IP addresses.

      o Seamless handover

        When a mobile device switches from one point of attachment to
        another (handover), existing communications should continue
        without packet loss or substantial delay. The mapping system
        must be dynamic to handle handover events with bounded latency.

      o Roaming

        Devices may roam from one administrative domain to another. The
        mapping systems in the home domain and remote domain may
        coordinate to persist existing communications using addresses
        that are local to the home domain.

      o Stateless mapping mode

        An address mapping system may provide a communication mode where
        the mapping information is carried in packets themselves. When a
        packet the contains such information enters a network, the
        information can be decoded to determine the identifier to
        locator mapping. This obviates the need for lookup in the
        mapping system for each packet.

1.3 Terminology

     Address Mapping System (AMS)
               A system for mapping addresses to other addresses.

     Address mapping system domain
               An administrative domain in which an address mapping
               system is run. The address mappings and related addresses
               are considered to be in a domain. An address mapping
               system domain implements a security policy to prevent
               unauthorized viewing or manipulation of mapping
               information.

     Mapping database/mapping table
               A logical or real database that contains all of the
               address mappings for an address mapping system domain.

     Mapping addresses
               The network addresses that are the objects in the address
               mapping system table. These are typical IPv4 or IPv6



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               addresses, but can generically be any type of fixed
               length network addresses.

     Identifier
               A mapping address that identifies an end node in network
               communication. In AMS, identifier generically refers to
               the key in an address mapping system database.

     Locator   A mapping address that refers to the location of a node.
               In AMS, locator generically refers to the addresses that
               a key maps to in the mapping system database.

     Mapping entry
               A single entry in a mapping domain. A mapping entry is
               composed of the key address (the identifier), one or more
               locators that the key maps to, and optional ancillary
               information.

     Mapping query
               A lookup in the address mapping system database. A key
               address (identifier) is provided and the corresponding
               map entry (containing locators) is returned if the key is
               matched in the table.

     Overlay forwarding
               The processing performed to implement a network overlay
               that forwards packets to the location for their
               destination address based on a mapping entry in the
               address mapping system. Overlay forwarding may be
               encapsulation, address transformations, etc.

     Overlay termination
               The processing done at the terminal endpoint of overlay
               protocol used in overlay forwarding.

     AMS router (AMS-R)
               A node that contains all or a shard of the addressing
               mapping system database. An AMS-R node serves mapping
               system information to AMS forwarding nodes. An AMS router
               node will often act at a packet router that performs
               overlay forwarding for addresses that it manages in the
               mapping system.

     AMS forwarders (AMS-F)
               A node that performs overlay forwarding and/or overlay
               termination. The AMS forwarder contains a mapping cache
               to facilitate overlay forwarding. End hosts may
               participate in the address mapping system as a



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               specialized type of a forwarder.

     Addressing Mapping Routing Protocol (AMRP)
               A protocol used amongst AMS routers to synchronize the
               mapping system database.

     Addressing Mapping Forwarder Protocol (AMFP)
               A control protocol run between AMS routers and AMS
               forwarders that is used to manage mapping caches in AMS
               forwarders.

     Firewall and Service Tickets (FAST)
               A protocol in which packets carry "tickets" in extension
               headers. Tickets provide arbitrary information about how
               a network processes packets.

     Hidden aggregation
               A method to encode aggregation in network addresses
               where the aggregation is visible to trusted devices
               within a  network, but is transparent to external
               observers of the  addresses.






























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2  Architecture

   This section describes the architecture of the Address Mapping
   System.

2.1  Reference topology

   This section provides a generic reference topology for AMS.

           +------------+        ___________        +------------+
           |   AMS-R    |       (  Shared   )       |    AMS-R   |
           | AMS router +-------( Database  )-------+ AMS router |
           +------+-----+       (___________)       +------+-----+
                  |                                        |
          +-------+--+----------+            +----------+--+-------+
          |          |          |            |          |          |
      +---+---+  +---+---+  +---+---+    +---+---+  +---+---+  +-------+
      | AMS-F |  | AMS-F |  | AMS-F |    | AMS-F |  | AMS-F |  | AMS-F |
      |       |  |       |  | Server|    |       |  |       |  | Server|
      +-------+  +-------+  +-------+    +-------+  +-------+  +-------+
          |          |                       |          |
      End hosts   End hosts              End hosts   End hosts

2.2 Functional components

   As shown in the reference topology, there are two types of functional
   nodes in the AMS architecture:

     AMS-R: AMS routers

     AMS-F: AMS forwarders

2.3 AMS router (AMS-R)

   AMS routers are deployed within the network infrastructure and
   collectively contain the address mapping database for an address
   mapping system domain. The database may be sharded across some number
   of routers for scalability. AMS routers that maintain the database or
   a shard may be replicated for scalability and availability. AMS
   routers share and synchronize mapping information amongst themselves
   using an Address Mapping Routing Protocol.

   AMS routers serve mapping information to AMS forwarders via the
   Address Mapping Forwarder Protocol. Mapping information is provided
   by a request/reply protocol, a push mechanism, or mapping redirects.

   An AMS router may perform overlay forwarding for the destination
   addresses it serves in the address mapping system database. Network



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   routing is configured so that packets with identifier addresses
   served by an AMS-R will be routed to that AMS-R.

   AMS routers are considered authoritative for the portion of that
   mapping database that they serve. For instance, if a packet with an
   identifier address is routed to an AMS-R then, either a mapping is
   found and the packet is forwarded via overlay forwarding, or the
   packet is dropped. In this sense, AMS routers can be thought of as
   anchor point when they are forwarding packets (in 3GPP terminology).

   An AMS router can send mapping redirects to AMS forwarders in order
   to inform them of a direct path they can take to a destination. A
   redirect is sent to the upstream AMS forwarder of the source which
   can be determined by a mapping query the source address. When an AMS
   forwarder receives a redirect, it can create a mapping cache entry
   and apply overlay forwarding on subsequent packets to directly send
   to the destination instead routing packets through a AMS router.

2.3.1 AMS router operation

   The operation of a forwarding AMS router is:

      1) Packet are routed to the AMS-R

      2) For each received packet, a lookup on the destination address
         is done in the mapping system database

      3) If a matching mapping entry is found in the address mapping
         database:

          o The packet is forwarded over a network overlay per the
            returned locator and ancillary information

          o Optionally, a mapping redirect is be sent to an AMS
            forwarder that is in that path from the source of the packet

      4) Else, the packet is dropped

2.4 AMS forwarder (AMS-F)

   As indicated in the reference topology, forwarding nodes may deployed
   near the point of device attachment (e.g. base station, eNodeB) of
   user devices (e.g. UEs).

   End hosts may act as AMS forwarders. These could be servers that
   provide overlay forwarding and termination on behalf of VMs or
   containers for virtualization. Since the source of packets is local
   on a host that is an AMS forwarder is, there may be some datapath



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   optimizations that can be applied.

   AMS forwarders have two functions:

      o Overlay termination which is restoring packet with original
        identifier addresses

      o Optional overlay forwarding to destinations based on a mapping
        cache

2.4.1 Overlay termination

   AMS forwarders perform overlay termination. In other words, they are
   typically the target node of a locator. Overlay termination is the
   process of removing or undoing the overlay processing that was
   previously done. If the overlay method is encapsulation, the overlay
   termination processing is to decapsulate the packet. If the overlay
   method is address transformation, such as in ILA, the overlay
   termination processing is to transform addresses back to their
   original values before overlay processing. Once the overlay
   processing is undone, an AMS forwarder forwards the resultant packet
   to its final destination.

2.4.2 Overlay forwarding

   An AMS forwarder may perform overlay fowarding to send packets
   directly to the destination using a cache of address mappings. The
   mapping cache of an AMS forwarder may be managed as a working set
   cache. As a cache there must be methods to populate, evict, and
   timeout entries. A cache is considered an optimization, so the system
   should be functional without it being used use (e.g. if the cache has
   no entries)

   The operation of overlay forwarding in an AMS forwarder is:

      1) Receive packets from downstream nodes

      2) Lookup up packet's destination address in the mapping cache

      3) If a match is found in the mapping cache then forward the
         packet over a network overlay per the returned locator and
         instructions

      4) Else, forward the unmodified packet in the network per normal
         routing

      5) An AMS router may send a mapping redirect in response to a
         packet that had been forwarded by the AMS forwarder. In



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         response, the forwarder may create a mapping cache entry based
         on the contents of the redirect and use the entry to send
         directly to a destination for subsequent packets.

3  Address Mapping Router Protocol (AMRP)

   AMS routers must synchronize the contents of the mapping database.
   When a change occurs to an address mapping, for instance a mobile
   device has moved to a new location,  the AMS routers managing the
   shard that contains the identifier must be synchronized in as little
   convergence time as possible.

   There are a number of options to use or have been used to implement
   an AMS mapping router protocol. This document highlights some
   alternatives, but does not prescribe a particular protocol.

3.1 Key/value database

   A key/value database, such as a NoSQL database like Redis, can
   implement an address mapping routing protocol. The idea of the
   database is that each mapping shard is a distributed database
   instance with some number of replicas. When a write is done in the
   database, the change is propagated throughout all of the replicas for
   the shard using the standard database replication mechanisms. Mapping
   information is written to the database using common database API that
   can require authenticated write permissions. Each AMS router can read
   the database for the associated shard to perform its function.

3.2 BGP

   BPG can be used to propagate mapping information amongst AMS routers
   as simple routes. [BGP-ILA] describes a method to distribute
   identifier to locator information using Multiprotocol Extensions for
   BGP-4.

3.3 3GPP uses GTP

4   Address Mapping Forwarder Protocol (AMFP)

   The Address Mapping Forwarder Protocol (AMFP) is a control plane
   protocol that provides address to address mappings. Clients of the
   AMFP include AMS forwarders with mapping caches, so AMFP includes
   primitives for mapping cache management.

   AMFP is primarily used between AMS forwarders and AMS routers. The
   purpose of the protocol is to populate and maintain the mapping cache
   in AMS forwarders.




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   AMFP defines mapping redirects, a request/response protocol, and a
   push mechanism to populate the mapping cache. AMFP runs over TCP to
   leverage reliability, statefulness implied by established
   connections, ordering, and security in the form of TLS. Secure
   redirects are facilitated by the use of TCP.

   AMFP messages are sent over the TCP stream and must be delineated by
   a receiver. Different versions of AMS are allowed and the version
   used for communication is negotiated by Hello messages.

4.1 Common header format

   All AMFP messages begin with a two octet common header:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type  |       Length          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The contents of the common header are:

     o Type: Indicates the type of message. A type 0 message is a Hello
       message. Types greater than zero are interpreted per the
       negotiated version.

     o Length: Length of the message in 32-bit words not including the
       first four bytes of the message. All AMFP messages are multiples
       of of four bytes in length and the message length includes the
       two bytes for the common header. The length field is computed as
       (message length / 4) - 1, so the minimum message size is four and
       the maximum size is 16,384 bytes.

   Following the two octet common header is variable length data that is
   specific to the version and type the message.

4.2 Hello messages

   Hello messages indicate the versions of AMFP that a node supports.
   Hello message MUST be sent by each side as the first message in the
   connection.

   The format of an AMFP Hello message is:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   0   |      Length             |R|  Rsvd     | MinV  | MaxV  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                               TLVs                            ~
      |                                                               |



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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The contents of the Hello message are:

     o Type = 0. This is indicates the type is a Hello message.

     o Router bit: Indicates the sender is an AMS router. If the sender
       is an AMS forwarder this bit is cleared.

     o Rsvd: Reserved bits. Must be set to zero on transmit.

     o MinV: Minimum version number supported by the sending node.

     o MaxV: Maximum version number supported by the sending node.

       o TLVs: An optional list of TLVs that describe capabilities or
       requested options.


   Version numbers are from 0 to 15. This document describes version 0
   of AMFP.

4.3 Hello Message TLVs

   TLVs (Type Length Values) MAY be used in AMFP Hello messages to
   convey optional information and parameters pertaining for
   negotiation. For example, a TLV could be used by an AMS-F to indicate
   the maximum number of mappings in its cache so that the AMS-R can
   managed redirects and pushed mappings accordingly.

   The format of the Hello message TLVs is:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Ver   | Length|    Type       |                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                           |
      |                                                           |
      ~                          TLV value                        ~
      |                                                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields of the Hello message TLV are:

      o Ver: Which version of AMFP the TLV refers to. This be one of the
        version numbers in the proposed range of the Hello message.

      o Length: Length of the TLV in 32-bit words not including the
        first four bytes. All Hello message TLVs have a size that is a
        multiple of four bytes. The minimum length of a TLV is four
        bytes and the maximum length is sixty-four bytes.



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      o Type: The type of the TLV. Type values are relative to the
        version stated in the Ver field so that each AMFP version has
        its own set of TLV types.

   A receiver MUST only process TLVs that are for the negotiated
   version. Before parsing the TLV list, the r3eceiver determines the
   negotiated AMFP version as described above. When parsing the list of
   TLVs, the node should skip over any TLVs that are not for the
   negotiated version.

   The high order bit if the TLV type indicates disposition of a type
   that is unrecognized. If the high bit is set for a TLV type that the
   receiver does not recognizes and the TLV if for the AMFP version that
   is being negotiated, then the receiver MUST terminate the connection.
   It MAY log the error.

4.2 Hello messages

   Hello messages indicate the versions of AMCP that a node supports.
   Hello message MUST be sent by each side as the first message in the
   connection.

   The format of an AMCP Hello message is:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  0    |           Length        |R|  Rsvd     | MinV  | MaxV  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                            TLVs                               ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The contents of the Hello message are:

     o Type = 0. This is indicates the type is a Hello message.

     o Router bit: Indicates the sender is an AMS router. If the sender
       is an AMS forwarder this bit is cleared.

     o Rsvd: Reserved bits. Must be set to zero on transmit.

     o MinV: Minimum version number supported by the sending node.

     o MaxV: Maximum version number supported by the sending node.

     o TLVs; An optional list of Type Length Value structures (TLVs).
       Use of TLVs in Hello messages is described below.




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   Version numbers are from 0 to 15. This document describes version 0
   of AMCP.

4.1.1 TLV format

   Hello message TLVs have the following format:

     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     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                          Value                                ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Fields:

     o Type: Type for TLV. Defined types are described below

     o Length: Length in bytes of a TLV Value. Note that this length
       does not include the two bytes for Type and Length.

     o Value: Data for the TLV

4.1.2 TLV types

   The table below lists the TLVs defined in this document. The "Length"
   column indicates any required limits on TLVs, and the "Typical
   Length" column indicates the most useful lengths for the TLV.

   Type   Length      Sender             Meaning
   ---------------------------------------------------------------------
   0                                     RESERVED
   1      1           Router             Default overlay method
   2      4           Router             Default timeout
   3      1           Router             Default priority
   4      1           Router             Default weight
   5      variable    Router             Default instructions
   6      variable    Either side        Supported overlay methods
   5-127                                 UNASSIGNED (assignable by IANA)
   128-255                               User defined

   The TLVs defined in this document apply to version 0.

4.1.3 Default overlay method




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   This TLV reports the default overlay method in report mapping
   information when the method is not explicitly provided in a mapping
   information message. The format of the TLV is:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type = 0x1    |  Length (1)   |    Overlay    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Fields are:

     o Overlay: Indicates the overlay method to be used when sending to
       the locator in the entry (e.g. ILA, LIST, SRv6, IPIP, GRE, etc.).
       A value of zero indicates that the default overlay method for the
       network or that negotiated by Hello messages.

   On AMS routers SHOULD send this TLV. If the TLV is received by a
   router it is considered an error.

4.1.4 Default timeout

   This TLV reports the default timeout for report mapping information
   when the timeout is not explicitly provided in a mapping information.

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Type = 0x2    |  Length (4)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Timeout                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Fields are:

     o Timeout: The time to live for the identifier information in
       seconds.

   Only AMS routers send this TLV. If the TLV is received by a router it
   is considered an error.

4.1.5 Default priority

   This TLV reports the default overlay priority in reported mapping
   information when the priority is not explicitly provided in a mapping
   information message. The format of the TLV is:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type = 0x3    |  Length (1)   |      Prio     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Fields are:



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     o Priority:  Relative priority of a locator. Locators with higher
       priority values have preference to be used. Locators that have
       the same priority may be used for load balancing.

   Only AMS routers send this TLV. If the TLV is received by a router it
   is considered an error.

4.1.6 Default weight

   This TLV reports the default weight in reported mapping information
   when the priority is not explicitly provided in a mapping information
   message. The format of the TLV is:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type = 0x4    |  Length (1)   |    Weight     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Fields are:

     o Weight: Relative weights assigned to each locator. In the case
       that locators have the same priority the weights are used to
       control how traffic is distributed. A weight of zero indicates no
       weight and the mapping is not used unless all locators for the
       same priority have a weight of zero.

   Only AMS routers send this TLV. If the TLV is received by a router it
   is considered an error.

4.1.6 Default instructions

   This TLV reports the default overlay specific instructions in
   reported mapping information when instructions are not explicitly
   provided in a mapping information message. The format of the TLV is:

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Type = 0x5    | Length ( >0 ) |    Overlay    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                         Instructions                          ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Fields are:

     o Instructions: Optional data with format and semantics that are
       specific to an overlay method and can describe options for the
       method how the overlay method is used.




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     o Overlay: Indicates the overlay method to be used when sending to
       the locator in the entry (e.g. ILA, LIST, SRv6, IPIP, GRE, etc.).
       A value of zero indicates that the default overlay method for the
       network or that negotiated by Hello messages. Only AMS routers
       send this TLV. If the TLV is received by a router it is
       considered an error.

4.1.5 Supported overlay methods

   This TLV reports the support overlay methods that a node supports.
   The TLV can be sent by either and MAS-R or an AMS-F and is a hint to
   the peer about what methods are supported. The format of the message
   is:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type = 0x3    |Length ( var.) |     Bit map
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Fields are:

     o Bit map:  A variable length bit map that indicates overlay
       methods. The position in the bip map corresponds to the defined
       values for the various overlay methods.

   Relative priority of a locator. Locators with higher priority values
   have preference to be used. Locators that have the same priority may
   be used for load balancing.

   Only AMS routers send this TLV. If the TLV is received by a router it
   is considered an error.

4.4  AMFP Version 0

   The message types in version 0 of AMFP are:

     o Map request (Type = 1)

     o Map information (Type = 2)

     o Compressed map information (Type = 3)

     o Locator unreachable (Type = 4)

4.4.1 Map request

   A map request is sent by an AMS forwarder to an AMS router to request
   mapping information for a list of identifiers. The format of a map
   request is:



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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   1   |       Length          |IDType |         Rsvd          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\
   |                                                               | |
   ~                         Identifier                            ~ ent
   |                                                               | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/

   The contents of the map request message are:

     o Type = 1. This is indicates the type is map request.

     o Length: Message length is set to size of an identifier times the
       number of identifiers in the list. The Length field is computed
       as identifier_size * number_of identifiers.

     o Rsvd: Reserved bits. Must be set to zero when sending.

     o IDType: Identifier type. Specifies the identifier type. This also
       implies the length of each identifier in the request list.
       Identifier types are defined below.

     o Identifier: An identifier of type indicated by IDType. The size
       of an identifier is specified by the type.

   The Identifier field is repeated for each identifier in the list. The
   number of identifiers being requested is (message length - 4) /
   (identifier size).

4.4.2 Map information

   A map information message is sent by an AMS router to provide
   identifier to locator mapping information. In addition to providing
   locators for an identifier, the message also contains the overlay
   method to use and related instructions for sending to an identifier.

   A map information message is composed four byte header followed by a
   set of identifier records. Each identifier record describes mapping
   information for one identifier. An identifier record is composed of a
   four byte header, an identifier, and a set of locator entries. Each
   locator entry provides the information about one locator used to
   reach an identifier. Each locator entry is composed of a four byte
   header that includes the overlay method to use, the locator, and
   instructions specific to the overlay method for the locator.

   The identifier record is repeated for each mapping being reported and
   the locator entry is repeated for each locator being reported for an
   identifier. The total number of identifiers being reported is



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   determined by parsing the message.

   The format of a map information message is:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   2   |       Length          | Reason|         Rsvd          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ <-+
   |IDType |            Record timeout             |  Num locator  |   \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   |                                                               |   |
   ~                            Identifier                         ~   |
   |                                                               |   r
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\  e
   |LocType| Ilen  |    OvMethod   |    Weight     | Prio  | Rsvd  | | c
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | o
   |                                                               | e r
   ~                            Locator                            ~ n d
   |                                                               | t |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ r |
   |                                                               | y |
   ~                         Instructions                          ~ | |
   |                                                               |/  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<--+

   The contents of the map information message header are:

     o Type = 2. This indicates an extended map information message

     o Length: The message length is four bytes plus the sum of lengths
       of all the identifier records in the message. The length of a
       record is four bytes plus the sum of all the lengths of locator
       entries in the record. The length of a locator entry is four plus
       the size of a locator plus the length of instruction field.

     o Reason: Specifies the reason that the message was sent. Reasons
       are:

       o 0: Map reply to a map request

       o 1: Redirect

       o 2: Push map information

     o Rsvd: Reserved bits. Must be set to zero when sending.

   The contents of an identifier record are:

     o IDType: Identifier type. Specifies the identifier type. This also



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       implies the length of each identifier in the list. Identifier
       types are defined below.

     o Record timeout: The time to live for the identifier information
       in seconds. A value of zero indicates the default is used.

     o Num locator: Number of locators (entries) being reported for an
       identifier.

     o Identifier: An identifier of type specified in IdType.

   The contents of a locator entry are:

     o LocType: Locator type. Specifies the locator type. This also
       implies the length of each locator in the list. Locator types are
       defined below.

     o Ilen: Length in 32-bit words of optional instructions in the
       entry (length of the instructions field). Instructions are
       overlay method specific and can describe options or or how the
       overlay is used. The instructions length is from zero to sixty
       bytes.

     o OvMethod: The overlay method to use for sending to the identifier
       using the given locator. This is an indication of the
       encapsulation method (e.g. GUE, GTP, LISP, etc.) or address
       transformation method (e.g. ILA). Specific values are listed in
       IANA section.

     o Weight: Relative weights assigned to each locator. In the case
       that locators have the same priority the weights are used to
       control how traffic is distributed. A weight of zero indicates no
       weight and the mapping is not used unless all locators for the
       same priority have a weight of zero.

     o Priority:  Relative priority of a locator. Locators with higher
       priority values have preference to be used. Locators that have
       the same priority may be used for load balancing.

     o Rsvd: Reserved bits. Must be set to zero when sending

     o Locator: A locator of type specified in LocType.

     o Instructions: Optional data with format and semantics that are
       specific to an overlay method and can describe options for the
       method how the overlay method is used. Ilen indicates the length
       of the field.




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4.4.3 Compressed map information

   The compressed map information message may be used as a mode
   efficient alternative to the map information message. The compressed
   map information can be used when:

      o There is only locator provided for each identifier, and

      o The overlay method, identifier type, locator type, and overlay
   instructions are common for all the mappings reported in the message,
   and

      o The identifier record timeout is common amongst the provided
   identifiers

   A compressed map information message is composed of an eight byte
   header followed by an optional instruction field, followed by a set
   of identifier/locator pairs. Each pair on identifier to locator
   mapping, and stated the overlay method and instructions are common to
   all the mappings in the message.

   The identifier/locator pairs are repeated for each mapping being
   reported. The total number of identifiers being reported can
   determined by parsing the message or computing it based on the
   message length and the lengths of the identifiers and locators.

   The format of the compressed map information message header is:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   3   |       Length          | Reason|IDType |LocType| Ilen  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   OvMethod    | Rsvd  |          Record timeout               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                          Instructions                         ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \
   |                                                               | |
   ~                            Identifier                         ~ e
   |                                                               | n
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ t
   |                                                               | |
   ~                            Locator                            | |
   |                                                               |/
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The contents of the compressed map information message header are:




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     o Type = 3. This indicates an compressed map information message

     o Length: Set to four plus the length of the instructions field
       plus the sum of lengths of the identifier/locator pairs in the
       message.

     o Reason: Specifies the reason that the message was sent. Reasons
       are:

        o 0: Map reply to a map request

        o 1: Redirect

        o 2: Push map information

     o IDType: Identifier type. Specifies the identifier type. This also
       implies the length of each identifier in the list. Identifier
       types are defined below.

     o LocType: Locator type. Specifies the locator type. This also
       implies the length of each locator in the list. Locator types are
       defined below.

     o Ilen: Length in 32 bit words of optional instructions in the
       entry (length of the instructions field). Instructions are
       overlay method specific and can describe options or or how the
       overlay is used. The instructions length is from zero to sixty
       bytes.

     o OvMethod: The overlay method to use for sending to the identifier
       using the given locator. This is an indication of the
       encapsulation method (e.g. GUE, GTP, LISP, etc.) or address
       transformation method (e.g. ILA). Specific values are listed in
       IAMA section.

     o Rsvd: Reserved bits. Must be set to zero when sending

     o Record timeout: The time to live for the identifier information
       in seconds. A value of zero indicates the default is used.

     o Instructions: Optional data with format and semantics that are
       specific to an overlay method and can describe options for the
       method or how the overlay methos is used. Ilen indicates the
       length of the field.

     o Identifier: An identifier of type specified in IdType.

     o Locator: A locator of type specified in LocType.



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4.4.4 Locator unreachable

   A locator unreachable message is sent by AMS routers to AMS
   forwarders in the event that a locator or locators are known to no
   longer be reachable. The format of a locator unreachable message is:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   4   |       Length          |     Rsvd      |LocType| Rsvd  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\
   |                                                               | |
   ~                           Locator                             ~ ent
   |                                                               | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/

   The fields of the locator unreachable message are:

     o Type = 4. This is indicates the type is a locator unreachable
       message.

     o Length: Set to the size of the locator times the number of
       locators in the list.

     o Rsvd: Reserved bits. Must be set to zero when sending.

     o LocType: Locator type. Specifies the locator type. This also
       implies the length of each locator in the list. Locator types are
       defined below.

     o Locator: A locator of type indicated by LocType. The size of a
       locator is specified by the type.

   The Locator field is repeated for each locator in the list. The
   number of locators being reported is (message length - 4) / (locator
   size).

4.4.5 Identifier and locator types

   Identifier and locator values used in IDType and LocType fields of
   AMCP messages are:


     o 0: Null value, 0 bit vlaue. This indicates that absence of
          locator or identifier information.

     o 1: IPv6 address, 128 bit value

     o 2: IPv4 address, 32 bit value




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     o 3: 32 bit index

     o 4: 64 bit index

     o 5: ILA value. A 64 bit value that represent a canonical ILA
          identifier when used in an IDType field and a canonical ILA
          locator when used in a LocType field.

   Note that the types for index values are use to index into tables
   for locators or identifiers.

4.5  Operation

   This section describes the operation of AMFP.

4.5.1 Version negotiation

   The first message sent by each side of an AMFP connection is a Hello
   message. Hello messages contain the minimum and maximum versions of
   AMCP supported. The minimum and maximum values form an inclusive
   range.

   When a host receives a AMFP Hello message, it determines which
   version is negotiated. The negotiated version is the maximum version
   number supported by both sides. For instance, if a node advertises a
   minimum version of 0 and maximum of 1 and receives a peer Hello
   message with a minimum version of 0 and maximum of 2; then the
   negotiated version is 1 since that is the greatest version supported
   by both sides. The peer host will also determine that 1 is the
   negotiated version.

   If there is no common version supported between the peers, that is
   their supported version ranges are disjoint, then version negotiation
   fails. The connection MUST be terminated and error message SHOULD be
   logged.

   If both sides set the router bit or both clear the router bit in a
   Hello message, then this is an error and the connection MUST be
   terminated and error message SHOULD be logged. Both sides cannot have
   the same role in an AMFP session.

4.5.2 Populating an mapping cache

   AMS forwarders can maintain a cache of identifier to locator
   mappings. There are three means for populating this cache:

     o Redirects




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     o Mapping request/reply

     o Pushed mappings

   Redirects are RECOMMNDED as the primary means of dynamically
   obtaining mapping information. Request/reply and push mappings may be
   used in limited circumstances, however generally these techniques
   don't scale and are susceptible to DOS attack.

   AMS forwarders (and AMS routers as well) are work conserving, they do
   not hold packets that are pending mapping resolution. If a node does
   not have a mapping for a destination in its cache then the packet is
   forwarded into the network; the packet should be processed by an AMS
   router and sent to the proper destination node.

4.5.3 Redirects

   An AMS router can send redirects in conjunction with forwarding
   packets. Redirects are sent to AMS forwarders in order to inform them
   of a direct AMS path. A redirect is sent to the upstream AMS
   forwarder of the source which is determined by a lookup in the
   mapping system on the source address of the packet being forwarded.
   The found locator is used to infer an address of the AMS forwarder.
   Note that this technique assumes a symmetric path towards the source.

4.5.3.1 Proactive push with redirect

   In addition to sending an AMFP redirect to the AMS forwarder, an AMS
   router MAY send an AMFP push to the AMS forwarder associated with the
   destination to inform it of the identifier to locator mapping for the
   source address in a packet. This is an optimization to push the
   mapping entry that can be used in the reverse direction of the
   communications. In order to do this, the AMS router performs a
   mapping lookup on the source address (which should already be done to
   perform the redirect). An AMFP push message is then sent to the
   forwarding node or host based on its locator.

4.5.3.2 Redirect rate limiting

   An AMS router SHOULD rate limit the number of redirects it sends to a
   forwarder for each redirected address. The rate limit SHOULD be
   configurable. The default rate limit SHOULD be to send no more than
   one redirect per second per redirected identifier. If a mapping
   change is detected the rate limiting SHOULD be reset so that
   redirects for a new mapping can be sent immediately.

4.5.4 Map request/reply




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   An AMS forwarder may send a map request message to obtain mapping
   information for a locator. If the receiving AMS router has the
   mapping information it responds with a map information message. If
   the router does not have a mapping entry for the requested
   identifier, it MAY reply with in a locator type of Null.

   Map requests are NOT RECOMMENDED as the primary means to dynamically
   populate entries in a mapping cache. The problem with this technique
   is that an AMS forwarder may generate a map request for each new
   destination that it gets from a downstream end host. A downstream end
   host could launch a Denial of Service (DOS) attack whereby it sends
   packets with random destination addresses that requires a mapping
   lookup. In the worst case scenario, the forwarder would send a map
   request for every packet received. Rate limiting the sending of map
   requests does not mitigate the problem since that would prevent the
   cache from getting mappings for legitimate destinations.

4.5.5 Push mappings

   An AMS router may push mappings to an AMS forwarder without being
   requested to do so. This mechanism could be used to pre-populate a
   mapping cache. Pre-populating the cache might be done if the network
   has a very small number of identifiers or there are a set of
   identifiers that are likely to be used for forwarding in most AMS
   forwarders (identifiers for common services in the network for
   instance). When a mapping router detects a changed mapping, the
   locator changes for instance, a new mapping can be pushed to the AMS
   forwarders.

   The push model is NOT RECOMMENDED as a primary means to populate an
   mapping cache since it does not scale. Conceivably, one could
   implement a pub/sub model and track of all AMS mappings and to which
   nodes the mapping information was provided. When a mapping changes,
   mapping information could be sent to those nodes that expressed
   interest. Such a scheme will not scale in deployments that have many
   mappings.

4.5.6 Cache maintenance

   This section describes maintenance of a mapping cache.

4.5.6.1 Timeouts

   A node SHOULD apply a timeout for a mapping entry that was indicated
   in a map information message. If the timeout fires then the mapping
   entry is removed. Subsequent packets may cause an AMS router to send
   a redirect so that the mapping entry gets repopulated in the cache.




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   The RECOMMENDED default timeout for identifiers is five minutes. If a
   node sends a map request to refresh a mapping, the RECOMMENDED
   default is to send the request ten seconds before the the mapping
   expires.

4.5.6.2 Cache refresh

   In order to avoid cycling a mapping entry with a redirect for a
   mapping that times out, a node MAY try to refresh the mapping before
   timeout. This should only be done if the cache entry has been used to
   forward a packet during the timeout interval.

   A cache refresh is performed by sending a map request for an
   identifier before its cache entry expires. If a map information
   message is received for the identifier, then the timeout can be reset
   and there are no other side effects.

4.5.7 AMS forwarder processing

   If an AMS forwarder receives to its local address (i.e. a locator
   address) a packet that has undergone overlay forwarding, it will
   perform overlay termination. It will check its local mapping database
   to determine if the identifier revealed in the packet after overlay
   termination is local. If the identifier is local, the forwarder will
   forward the packet on to its destination which is either a downstream
   node that the forwarder has a route to, or a local VM or container in
   the case that the forwarder is an end host.

   If the identifier is not local then the AMS forwarder forwards the
   packet back into the network after overlay termination. This may
   happen if an end node has moved to be attached to a different AMS
   forwarder and the new locator has not yet been propagated to all AMS
   nodes. The packet should traverse an AMS router which can send a
   mapping redirect back the source's AMS forwarder as described above.
   To avoid infinite loop in this process, the forwarder must decrement
   TTL in the packet being forwarded.

   When a node migrates its point of attachment from one forwarder to
   another, the local mapping on the old node is removed so that any
   packets that are received and destined to the migrated identifier are
   re-injected without the overlay.  A "negative" mapping with timeout
   may also be set ensure that the node is able to infer the destination
   address is a proper identifier for the mapping domain (e.g. would be
   needed with foreign identifiers).

4.5.8 Locator unreachable handling

   When connectivity to a locator is loss, the mapping system should



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   detect this. A locator unreachable message MAY be sent by AMS routers
   to AMS forwarders to inform them that a locator is no longer
   reachable. Each forwarder SHOULD remove any cache entries using that
   locator and MAY send a map request for the affected identifiers.

4.5.9 Control Connections

   AMS forwarders must create AMFP connections to all the AMS routers
   that might provide routing information. In a simple network there may
   be just one router to connect to. In a more complex network with AMS
   routers for a sharded and replicated mapping system database there
   may be many. A list of AMS routers to connect to is provided to each
   AMS forwarder. This list could be provided by configuration, a shared
   database, or an external protocol to AMCP.

   Conceivably, the number of AMS routers in a network that might report
   mapping information could be quite large (into the thousands). If
   managing a large number of connections at the AMS forwarders is
   problematic, AMS router proxies could be used that consolidate
   connections as illustrated below:

      +-------+    +-------+    +-------+     +-------+    +-------+
      | AMS-R |    | AMS-R |    | AMS-R |     | AMS-R |    | AMS-R |
      +---+---+    +---+---+    +---+---+     +---+---+    +---+---+
          |            |            |             |            |
          |          +-+------------+-------------+-+          |
          +----------+            AMFP              +----------+
                     |            PROXY             |
          +----------+                              +----------+
          |          +-+------------+-------------+-+          |
          |            |            |             |            |
      +---+---+    +---+---+    +---+---+     +---+---+    +-------+
      | AMS-F |    | AMS-F |    | AMS-H |     | AMS-F |    | AMS-F |
      +---+---+    +---+---+    +---+---+     +---+---+    +---+---+

   In the above diagram a single AMS router proxy serves five AMS
   routers and five AMS forwarders. The proxy creates one connection to
   each AMS router and each AMS forwarder creates one connection to the
   proxy.

4.5.10 Protocol errors

   If a protocol error is encountered in processing AMFP messages then a
   node MUST terminate the connection. It SHOULD log the error and MAY
   attempt to restart the connection. There are no error messages
   defined in AMFP.

   Protocol errors include mismatch of length for given data, reserved



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   bits not set to zero, unknown identifier type or locator types,
   unknown reason, unknown overlay type or instructions, and loss of
   message synchronization in a TCP stream. Note that if the end of a
   message does not end on field or record boundary this also considered
   a protocol error.

5  Stateless mapping optimization

   An alternative to requiring a mapping lookup on each packet is to
   encode the mapping information in packets themselves. This can be
   achieved by encoding mapping information in Firewall and Service
   Tickets. The basic concept is that mapping information is encoded in
   FAST tickets which are attached in packets at the end hosts and
   interpreted by the network. Tickets are associated with flows and are
   set in all the packets for the flow. Ticket reflection ensures that
   packets sent in the return path of a flow include a ticket.

5.1  Firewall and Service Tickets encoding

   FAST tickets are encoded in Hop-by-Hop options. The format of a FAST
   ticket in a Hop-by-Hop option is:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Option Type  |  Opt Data Len | Prop  |  Rsvd |     Type      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                            Ticket                             ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   [FAST] suggests a simple and efficient encoding of a Service Profile
   Index:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Option Type  |  Opt Data Len | Prop  |LocType|     Type      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Expiration time                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Service Profile Index                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This format can be amended to include address mapping encoding.

5.2  Address mapping encoding

   A locator address can directly encode in a ticket. Different address
   types can be used. A ticket with expiration time, service profile and



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   locator address may have format:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Option Type  |  Opt Data Len | Prop  |LocType|     Type      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Expiration time                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Service Profile Index                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                           Locator                             ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Pertinent fields are:

      o LocType: Locator type. Specifies the locator type. This also
        implies the length the locator in the list. Locator types        are
        defined above.

      o Service Profile Index: Can encode the overlay method and a
        limited set of instructions for overlay forwarding.

      o Locator: A locator of type indicated by LocType. The size of a
        locator is specified by the type.

   A network may have a comparatively small number of locators. For
   instance, a mobile provider might associate each eNodeB with a
   locator and there may only be a few million of these. In this case,
   the border routers might maintain a static table of locator addresses
   that can simply be indexed by number in a small range. Similarly, the
   backend server in the layer 4 load balancing case might also be
   indicated by an index into a table of backend servers.

5.3 Reference topology

   As show in the reference topology below, FAST routers and AMS
   forwarders are involved in the stateless mapping datapath. AMS
   routers are not directly involved in the data path, however they
   serve the mapping information to be encoded into FAST tickets.

   FAST routers interpret tickets and perform overlay forwarding. AMS
   forwarders terminate overlay forwarding. Note that an AMS forwarder
   and FAST router would be co-located so that a node processes FAST
   tickets and does AMS forwarding base on that.

                                 Internet



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                                     |
                            +-----------+---------+
                            |    FAST   |  AMS-F  |
                            |   router  |         |
                            +-----------+---------+
                                     |
    +-----------+---------+     _____|_____     +------------+---------+
    |    FAST   |  AMS-F  |    (           )    |    FAST    |  AMS-F  |
    |   router  |         +----(  Network  )----+   router   |         |
    +-----------+---------+    (___________)    +------------+---------+
                                    |
                         +----------+----------+
                         |          |          |
                     +---+---+  +---+---+  +---+---+
                     | AMS-F |  | AMS-F |  | AMS-F |
                     +-------+  +-------+  +-------+
                         |          |
                      End hosts  End hosts

5.4  Operation

   This section describes the operation of encoding mapping entries in
   FAST tickets.

5.4.1 Ticket requests

   Applications request FAST tickets from a ticket agent in the network
   local to the application. The ticket agent can return a ticket for
   the application to use in its data packets. The ticket includes
   information that is parsed by elements in the issuing network. The
   ticket information may include routing information. For example, if
   the application is on a mobile device, the network may provide a
   ticket that has a locator indicating the current location of the
   device.

   [FAST] describes the process of an application requesting tickets and
   setting them in packets. An application will not normally need to
   make any special requests for routing information and the use of
   routing information is expected to be transparent to the application.

5.4.2 Qualified locators

   There are two possibilities for locator information in an issued
   ticket:

      o The locator is fully qualified.

      0 The locator is not qualified.



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5.4.2.1 Fully qualified locators

   If a locator is qualified then the issued ticket contains the
   locator for the end node. If the locator changes, that is the node
   moves, then a new ticket will need to be issued to the application.

5.4.2.2 Unqualified locators

   If the locator is not qualified, then the locator information in the
   issued ticket contains a "not set" value. For instance, in the case
   the locator is expressed by a Locator Index then the "not set" value
   may be -1 (all ones). The AMS forwarder in the upstream path of an
   end node may write a locator value into the locator information to
   make it qualified; most often this would just be its own locator
   value in cases where it is the first upstream hop of an end devices
   that coincides with an AMS forwarder that provides location in the
   network. The implication is that this will be the locator used in the
   network overlay on the return path to reach the end node. Note that
   to write a locator into to a ticket requires that the ticket is in a
   modifiable Hop-by-Hop option.

5.4.3 AMS forwarder processing

   Once an application has been issued a ticket with mapping information
   it will set the ticket in all packets sent to the peer node. The
   first hop upstream router, which might also be an AMS forwarder, in
   the FAST domain parses the ticket-- this may typically be the first
   hop router in a provider network closest to end user nodes.

   If the ticket contains a qualified locator, the first hop node may
   validate it (as part of FAST ticket validation). If the ticket has
   unqualified locator information, the first hop node may set it to a
   qualified locator value in the packet. As described above, the
   locator information written is likely to be that corresponding to the
   locator of the first hop device which is an AMS forwarder.

5.4.4 Transit to the peer

   Beyond the first hop router to the ultimate peer destination, no
   processing of mapping information in a ticket should be needed.
   Intervening networks and routers should deliver the ticket to the
   destination host unchanged.

   At the peer host, the procedures described in [FAST] are followed to
   save the received ticket in a flow context and to reflect it in
   subsequent packets. As with other reflected tickets, one containing
   mapping information is treated as an opaque value that is not parsed
   or modified by the peer or any network outside of the origin network.



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   Packets sent by a peer will include reflected tickets for a flow. No
   processing of reflected mapping information in a ticket should be
   needed until the packet reaches the origin network of the ticket.
   Intervening networks and routers should deliver the ticket to the
   destination origin network unchanged.

5.4.5 Ingress into the origin network

   At a border FAST router for the origin network, tickets are parsed
   and the encoded services are applied. If a ticket contains mapping
   information then the FAST router uses the information to perform
   overlay forwarding to the destination (the function of an AMS-F).
   Note that the FAST router performs no map query and does not need to
   maintain a mapping cache.

   The service parameters contained in the ticket may provide additional
   instructions about how the packet is to be sent over the network
   overlay. For instance, the service parameters might indicate the
   packet is encrypted or to use some extensions of an encapsulation
   protocol.

5.4.6 Overlay termination

   When a forwarded packet is received at the targeted AMS-F, normal
   procedures for overlay termination and forwarding the packet on to
   its destination are done.

   At the end host, received reflected tickets are validated for
   acceptance as described in [FAST]. This is done by comparing the
   received ticket to that which was sent on the corresponding flow.

5.4.7 Fallback

   The proposal described here is considered an optimization. Routing
   information in FAST tickets is not intended to completely replace a
   routing infrastructure. In particular, this solution relies on
   several parties to implement protocols correctly. For instance, the
   use of extension headers requires that they can be successfully sent
   through a network. As reported in [RFC7872], Internet support for
   forwarding packets with extension headers is not yet ubiquitous.

   Therefore, a fallback is required when encoding mapping information
   in FAST is not viable for a flow.  The fallback in AMS is to route
   packets through AMS routers.

5.4.8 Mobile events

   When a mobile node moves and its locator changes, it is desirable to



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   converge to using the new locator as a quickly as possible. With
   tickets that contain locator information, a modified ticket needs to
   be sent to a peer host.

   If an application was issued a ticket with qualified locator
   information then a new ticket needs to be issued. This can be done by
   the application receiving a signal that a mobile event has occurred
   causing it to make new ticket requests for established flows.

   If an application has a ticket with an unqualified locator then the
   network should start writing the new locator information into packets
   that are sent by the application after the mobile event. This should
   be transparent to the application.

   Note that in either case, in order to update the tickets that a peer
   is reflecting, the application needs to send packets to the peer that
   includes an updated ticket. There is no guarantee when an application
   may send packets, so there is the possibility of a window where the
   peer node is sending reflected tickets with outdated locator
   information. The window should be limited by the expiration time of a
   ticket (see below), however it is recommended to implement mechanisms
   to avoid communication blackholes. For instance, a "care of address"
   mapping entry could be installed at the old locator node to forward
   to the new one. Such solutions are also used to mitigate database
   convergence time or cache synchronization time.

5.4.10 Interaction with expired tickets

   FAST typically expects ticket to have an expiration time. If a ticket
   is received before the expiration time and it is otherwise valid,
   then the packet is forwarded per the services indicated by the
   ticket. If a packet is received with an expired ticket, it might
   still be accepted subject to rate limiting. Accepting expired tickets
   is useful in the case that a connection goes idle and after some time
   the remote peer starts to send.

   For tickets that are expired and contain mapping information, a FAST
   router should ignore the mapping information and take the fallback
   path. When an application sends new packets, it can include a fresh
   ticket so that the fast path is taken on subsequent packets. Ignoring
   the mapping information in expired tickets puts an upper bound on the
   window that outdated information can be used.

6  Privacy in Internet addresses

   This section discusses the interaction between the address mapping
   system and privacy in Internet addressing. An address mapping system
   can facilitate strong privacy in Internet addressing. [ADDR-PRIV]



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   discusses privacy in addressing.

6.1 Criteria for privacy in addressing

   Per [ADDR-PRIV], the ideal criteria for IPv6 addresses that provide
   strong privacy are:

      o Addresses are composed of a global routing prefix and a suffix
        that is internal to an organization or provider. This is the
        same property for IP addresses [RFC4291].

      o The registry and organization of an address can be determined by
        the network prefix. This is true for any global address. The
        organizational bits in the address should have minimal hierarchy
        to prevent inference. It might be reasonable to have an internal
        prefix that divides identifiers based on broad geographic
        regions, but detailed information such as location, department
        in an enterprise, or device type should not be encoded in a
        globally visible address.

      o Given two addresses and no other information, the desired
        properties of correlating them are:

          o It can be inferred if they belong to the same organization
            and registry. This is true for any two global IP addresses.

          o It may be inferred that they belong to the same broad
            grouping, such as a geographic region, if the information is
            encoded in the organizational bits of the address.

          o No other correlation can be established. It cannot be
            inferred that the IP addresses address the same node, the
            addressed nodes reside in the same subnet, rack, or
            department, or that the nodes for the two addresses have any
            geographic proximity to one another.

      o Geographic location of a node cannot be deduced from an address
        with accuracy.

      o Given two observed addresses, no strong correlations can be
        drawn. In particular it must not be possible to correlate that
        two different flows originate from the same user.

6.2  Achieving strong privacy

        Strong privacy in addressing can be achieved by using a
        different randomly generated identifier source address for each
        flow. Conceptually, this would entail that the network creates



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        and assigns a unique and untrackable address to a host for every
        flow created by the host.

        In this scheme, each host would be assigned many addresses which
        are non-topological in the local network to both promote privacy
        and mobility. An identifier-locator protocol with an address
        mapping system can provide reachability. This would entail that
        the addressing mapping system contains a mapping entry for each
        ephemeral address.

        In large networks this solution presents an obvious scaling
        problem. Assigning an address per connection is a potential
        scaling problem on two accounts:

      o The amount of state needed in the address mapping system is
        significant.

      o Bulk host address assignment is inefficient.

6.3 Scaling network state

   The amount of state necessary to assign each flow its own unique
   source IP address is equivalent, or at least proportional, to the
   amount of state needed for CGNAT-- basically this is one state
   element for every connection in the network. So in one sense this
   solution should scale as well as NAT has.

6.3.1 Hidden aggregation

   A possible solution to reduce state is to make addresses aggregable,
   but use an aggregation method that is known only by the network
   provider and hidden to the rest of the world. The network could use a
   reversible hash or encryption function to create addresses. This
   method is called "hidden aggregation".

   The input to an address generation function includes a group
   identifier, a secret key, and a generation index.

   The function may have the form:

         Address = Func(key, group_ident, gen)

   Where "key" is secret to network, "group_ident" is a network internal
   identifier for an aggregated set of addresses (roughly equivalent to
   "identity" in IDEAS), and "gen" is generation number 0,1,2,... N. The
   generation value is changed for each invocation to create different
   addresses for assignment to a node.




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   When a network ingress node is forwarded a packet it performs the
   inverse function on an address.

   The inverse function has the form:

         (group_ident, gen) = FuncInv(key, Address)

   The returned group_ident value is used as the identifier in the
   mapping lookup for a locator address. In this manner, the network can
   generate many addresses to assign to a node where they all share a
   single entry in the mapping system.

6.3.2 Address format

   A possible address format for hidden aggregation is shown below.

    <------------ 64 bits ----------><--- 32 bits ---><--- 32 bits --->
     +-------------------------------+----------------+----------------+
     |        Provider prefix        |   Key selector |  Address bits  |
     +-------------------------------+----------------+----------------+

   Note the that provider prefix is not hidden, so the address does
   identify the network provider of a user. Key selector is an index
   into a table of keys. A key table should have at least 2^16 entries
   that are randomly generated and securely shared amongst AMS routers.
   Hosts can be assigned addresses in blocks based on a key, however the
   same key should be used for different hosts assignments and end hosts
   should be assigned blocks from different keys.

   The address bits are used to create unique addresses per key. A
   decoded address may contain a magic value to verify the hash
   function.

   Keys should be rotated periodically. Addresses assigned using a
   particular key will therefore have an expiration, the default
   expiration time should be one week (assuming one of 2^16 keys in
   table are rotated each minute).

6.3.3 Practicality of hidden aggregation methods

   The premise of hidden aggregation is that only trusted devices in the
   network are able decode the aggregation hidden within IPv6 addresses.
   This implies that the network must keep secrets about the process. In
   the above examples, the secrets are keys used in the hash or
   encryption. The security of the key is then paramount, so techniques
   for key management, rotation, and using different key sets for
   obfuscation are pertinent.




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   To perform a mapping lookup a node must apply the inverse address
   generation function to map addresses to their group identifiers. This
   lookup would occur in the critical data path so performance is
   important. Encryption and hashing are notoriously time consuming and
   computationally complex functions.

   Some possible mitigating factors for performance impact are:

      o The input to address generation functions is a small amount of
        data and has fixed size. The input is a key (presumably 128 or
        256 bits), part of all of an IPv6 address (128 bits), and a
        generation number (sixteen to twenty-four bits should work).

      o Given that the input is fixed size, specialized hardware might
        be used to optimize performance of the inverse address
        generation function. For instance, modern CPUs include
        instructions to perform crypto [AES-NI]. Since the keys used in
        these functions are secret to the network and there are
        relatively few of them, they might be preloaded into a crypto
        engine to reduce setup costs.

      o The output of an inverse address generation function is
        cacheable. A cache on a device could contain address to locator
        mappings. When the inverse function and lookup on group_ident
        are performed, a mapping of address to the discovered locator
        could be created in the cache. The node could then map addresses
        in subsequent packets sent on the same flow to the proper
        locator by looking up the address in the cache.

6.4 Scaling bulk address assignment


   Assigning multiple addresses without aggregation is difficult to
   scale. Each address would need to be individually specified in an
   assignment sent to a host.

   DHCPv6 might allow bulk singleton address assignment. As stated in
   [RFC7934]:

      Most DHCPv6 clients only ask for one non-temporary address, but
      the protocol allows requesting multiple temporary and even
      multiple non- temporary addresses, and the server could choose to
      provide multiple addresses.  It is also technically possible for a
      client to request additional addresses using a different DHCP
      Unique Identifier (DUID), though the DHCPv6 specification implies
      that this is not expected behavior ([RFC3315], Section 9).  The
      DHCPv6 server will decide whether to grant or reject the request
      based on information about the client, including its DUID, MAC



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      address, and more. The maximum number of IPv6 addresses that can
      be provided in a single DHCPv6 packet, given a typical MTU of 1500
      bytes or smaller, is approximately 30.

7  Address Mapping System in 5G networks

   The section describes applying AMS for use in 5G networks. AMS is
   instantiated as a function in the 5G services architecture described
   in [3GPPTS].

7.1 Architecture

   The figure below depicts the use of AMS in a 5G reference point
   architecture. AMS is logically a network function and AMS interfaces
   to the 5G control plane via service based interfaces.

                        Service Based Interfaces
    ----+-----+----+----+----+----+----+--------+----+--------
        |     |    |    |    |    |    |        |    |
    +---+---+ | +--+--+ | +--+--+ | +--+--+  +--+--+ |
    | NSSF+ | | | NRF | | | DSF | | | UDM |  | NEF | |
    +-------+ | +-----+ | +-----+ | +-----+  +-----+ |
              |         |         |                  |
         +----+--+  +--+--+  +---+--+  +-------------+--+
         |  AMF  |  | PCF |  | AUSF |  |AMS CP-SMF/GTPC |
         +---+-+-+  +-----+  +------+  +-+-----+--------+     ^
   +-------+ | |                         |     |              |
   | 5G UE |-+ |                   +-----+     |       +- N4 -+
   +---+---+   | N2                |           |       |
       |       |             +-----+----+  +---+---+   V  +----+
       |       |      +------|  AMS-F/R |--| AMS-R |------| DN |
       |       |      |  N3  +-+---+--+-+  +-+-----+      +----+
       |       |      |        |   |  |      |
       |     +-+------+---+    +---+  +------+
       +-----|    gNB     |       N9       N9
       |     +------------+
       |                       +-----+----+  +---+---+      +----+
       |                +------|  UPF     |--| UPF   |------| DN |
       |                |  N3  +-+---+--+-+  +-+-----+      +----+
       |                |        |   |  |      |
       |     +----------+-+      +---+  +------+
       +-----|    gNB     |       N9       N9
             +------------+

            Figure 2: AMS in 5G reference point architecture

   AMS is used over the N3 and N9 interface. Address mappings in the
   downlink from the data network are done by an AMS-R. Transformations



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   for edge traffic can be done by an AMS-F close to the gNB or by an
   AMS-R in the case of a cache miss.

   The control interface into AMS is via N4 interface that interacts
   with 5G network services. AMS Control Plane node (AMS-CP) uses
   RESTful APIs to make requests to network services (see section 7.3).
   An AMS-CP receives notifications when devices enter the network,
   leave it, or move within the network. The AMS-CP writes the address
   mapping entries accordingly.

   AMS-CP communicate with other AMS-CPs, AMS-Fs, and AMS-Rs in the same
   routing domain via control protocols that are independent of the 5G
   control plane. The mapping database is shared amongst AMS-CP and AMS-
   Rs utilizing underlying distributed database technology deployed.

7.2 Protocol layering

   Figure 3 illustrates the protocol layers of packets packets sent over
   various data plane interfaces in the downlink direction of data
   network to a mobile node. Note that this assumes the topology shown
   in Figure 2 where GTP-U is used over N3 and IP routing is used on N9.

               --->             --->            --->
    DN to AMS-R    AMS-R to AMS-F  AMS-F to gNB     gNB to UE
   +-----------+   +-----------+   +------------+   +------------+
   |  Applic.  |   |   Applic. |   |   Applic.  |   |   Applic.  |
   +-----------+   +-----------+   +------------+   +------------+
   |    L4     |   |     L4    |   |     L4     |   |     L4     |
   +-----------+   +-----------+   +------------+   +------------+
   |    IP     |   |     IP    |   |    IP      |   |  PDU Layer |
   +-----------+ | +-----------+ | +------------+   +------------+
   |    L2     | | |     L2    | | |   GTP-U    |   | AN Protocol|
   +-----------+ | +-----------+ | +------------+   |   Layers   |
                 |               | |   UDP/IP   |   |            |
                N6  <--N9 -->   N3 +------------+   +------------+
                                   |    L2      |
                                   +------------+

         Figure 3: AMS and protocol layer in Downlink core

                <---            <---            <---
    AMS-H to VM    AMS-F to AMS-H   gNB to AMS-F     UE to gNB
   +-----------+   +-----------+   +-----------+   +-----------+
   |  Applic.  |   |  Applic.  |   |  Applic.  |   |  Applic.  |
   +-----------+   +-----------+   +-----------+   +-----------+
   |     L4    |   |     L4    |   |     L4    |   |     L4    |
   +-----------+   +-----------+   +-----------+   +-----------+
   |     IP    |   |     IP    |   |    IP     |   | PDU Layer |



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   +-----------+ | +-----------+ | +-----------+   +-----------+
   |     L2    | | |Overlay    | | |   GTP-U   |   | AN Protocol|
   +-----------+ | +-----------+ | +-----------+   |   Layers  |
                 | | UDP/IP    | | |   UDP/IP  |   |           |
                 | +-----------+   +-----------+
                   |     L2    |   |    L2     |
                   +-----------+   +-----------+

             Figure 3: AMS and protocol layer in uplink MEC

7.3 Control plane between AMS and network

   AMS is a consumer of several 5G network services. The service
   operations of interest to AMS are:

      o Nudm (Unified Data Management): Provides subscriber information.

      o Nsmf (Service Managment Function): Provides information about
        PDU sessions.

      o Namf (Core Access and Mobility Function): Provides notifications
        of mobility events.

   AMS-CP subscribes to notifications from network services. These
   notifications drive changes in the address mapping table. The service
   interfaces reference a UE by UE ID (SUPI or IMSI-Group Identifier),
   this is used as the key in the AMS identifier database to map UEs to
   addresses and identifier groups. Point of attachment is given by gNB
   ID, this is used as the key in the AMS locator database to map a gNB
   to an AMS-F and its locator.

7.4 AMS and network slices

   Figure 4 illustrates the use of network slices with AMS.

   ----+-------------------------------------+--------------------
       |                                     |
   +-------------------------+   +----------------------------+
   |  +--------+       Slice |   |  +-------------+     Slice |
   |  |  SMF   |-----+    #1 |   |  |  AMS-CP      |----+   #2|
   |  +---+----+     |       |   |  +-----------+-+    |      |
   |  N4  |          | N4    |   |        |     |      |      |
   |  +---+--+    +--+----+  |   |  +--------+  |  +--+----+  |   +----+
   |  |  UPF  |   | UPF   |  |   |  | AMS-F  |  |  | AMS-R |  |---| DN |
   |  +-------+   +-------+  |   |  +--------+  |  +-------+  |   +----+
   +-------------------------+   +--------------|-------------+
                      |                         |
                   +--+-+          +------------|-------------+



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                   | DN |          |            |       Slice |
                   +----+          |     +------+----+     #3 |
                                   |     |           |        |
                                   | +-------+     +-------+  |   +----+
                        +-----+    | | AMS-F |     | AMS-R |  |---| DN |
                        | MEC |----| +-------+     +-------+  |   +----+
                        +-----+    +--------------------------+

                         Figure 4: AMS and network slices in 5G

   In this figure, slice #1 illustrates legacy use of UPFs without AMS
   in a slice. AMS can be deployed incrementally or in parts of the
   network. As demonstrated, the use of network slices can provide
   domain isolation for this.

   Slice #2 supports AMS. Some number ofAMS-Fs and AMS-Rs are deployed.
   Address transformations are performed over the N9 interface. AMS-Rs
   would be deployed at the N6 interface to perform address
   transformations on packets received from a data network. AMS-Fs will
   be deployed deeper in the network at one side of the N3 interface.
   AMS-Fs may be supplemented by AMS-Rs that are deployed in the
   network. AMS-CP manages the mapping database within the slice.

   Slice #3 shows another slice that supports AMS. In this scenario, the
   slice is for Mobile Edge Computing. The slice contains AMS-Rs and
   AMS-Fs, and as illustrated, it may also contain End hosts that run
   directly on edge computing servers. Note in this example, one AMS-CP,
   and hence one routing domain, is shared between slice #2 and slice
   #3. Alternatively, the two slices could each have their own AMS-CP
   and define separate routing domains.

7.4 AMS in 4G networks

   The 4G architecture in 3GPP implements an address mapping system that
   is consistent with the architecture described in this document.
   Serving gateways have the role of AMS routers and GTP-U is the AMS
   routing protocol in 3GPP. 3GPP is based on an anchored routing model,
   the protocol can be augmented with AMS forwarders to achieve
   anchorless routing. Note that this can be done as an incremental
   addition to the 3GPP model, and in particular the core model and
   protocols of 3GPP, including GTP-C and GTP-C, require no change. The
   addition of AMS forwarders and mapping caches is done as an
   optimization for handling critical, low latency applications.

7.5 Overlay forwarding

   As described in section X, AMS forwarders may be implemented on
   servers. For instance, a mobile network may have server farms that



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   provide VMs for running services close to users. For both performance
   and feasibility, it may be preferable for such servers to use an
   alternative overlay method than GTP. This document highlights that
   Generic UDP Encapsulation (UE) or Identifier Locator Addressing (ILA)
   may be good alternatives. GUE is a generic and extensible
   encapsulation protocol with good performance, ILA is
   identifier/locator split protocol that works with IPv6 and has very
   good performance.

8  Security Considerations

   AMFP must have protection against message forgery. In particular
   secure redirects and mapping information message are required to
   prevent and attacked from spoofing messages and illegitimately
   redirecting packets. This security is provided by using TCP
   connections so that origin of the messages is never ambiguous.

   Transport Layer Security (TLS) [RFC5246] MAY be used to provide
   secrecy, authentication, and integrity check for AMFP messages.

   The TCP Authentication Option [RFC5925] MAY be used to provide
   authentication for AMFP messages.





























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9  IANA Considerations

10  References

10.1  Normative References

   [RFC8200]   Deering, S. and R. Hinden, "Internet Protocol, Version 6
               (IPv6) Specification", STD 86, RFC 8200, DOI
               10.17487/RFC8200, July 2017, <https://www.rfc-
               editor.org/info/rfc8200>.

   [RFC4291]   Hinden, R. and S. Deering, "IP Version 6 Addressing
               Architecture", RFC 4291, February 2006.

   [ILA]       Herbert, T., and Lapukhov, P., "Identifier Locator
               Addressing for IPv6" draft-herbert-intarea-ila-00

10.2  Informative References

   [RFC5246]]  Dierks, T. and E. Rescorla, "The Transport Layer Security
               (TLS) Protocol Version 1.2", RFC 5246, DOI
               10.17487/RFC5246, August 2008, <https://www.rfc-
               editor.org/info/rfc5246>.

   [RFC5925]   Touch, J., Mankin, A., and R. Bonica, "The TCP
               Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
               June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [BGPILA]    Lapukhov, P., "Use of BGP for dissemination of ILA
               mapping information" draft-lapukhov-bgp-ila-afi-02

Author's Address

   Tom Herbert
   Quantonium
   Santa Clara, CA
   USA

   Vikram Siwach

   Email: tom@quantonium.net










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