SIPP: Simple Internet Protocol Plus White Paper

Network Working Group:                                         R. Hinden
Request for Comments: 1710                              Sun Microsystems
Category: Informational                                     October 1994


               Simple Internet Protocol Plus White Paper

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Abstract

   This document was submitted to the IETF IPng area in response to RFC
   1550.  Publication of this document does not imply acceptance by the
   IPng area of any ideas expressed within.  Comments should be
   submitted to the author and/or the sipp@sunroof.eng.sun.com mailing
   list.

1. Introduction

   This white paper presents an overview of the Simple Internet Protocol
   plus (SIPP) which is one of the candidates being considered in the
   Internet Engineering Task Force (IETF) for the next version of the
   Internet Protocol (the current version is usually referred to as
   IPv4).  This white paper is not intended to be a detailed
   presentation of all of the features and motivation for SIPP, but is
   intended to give the reader an overview of the proposal.  It is also
   not intended that this be an implementation specification, but given
   the simplicity of the central core of SIPP, an implementor familiar
   with IPv4 could probably construct a basic working SIPP
   implementation from reading this overview.

   SIPP is a new version of IP which is designed to be an evolutionary
   step from IPv4.  It is a natural increment to IPv4.  It can be
   installed as a normal software upgrade in internet devices and is
   interoperable with the current IPv4.  Its deployment strategy was
   designed to not have any "flag" days.  SIPP is designed to run well
   on high performance networks (e.g., ATM) and at the same time is
   still efficient for low bandwidth networks (e.g., wireless).  In
   addition, it provides a platform for new internet functionality that
   will be required in the near future.

   This white paper describes the work of IETF SIPP working group.
   Several individuals deserve specific recognition.  These include
   Steve Deering, Paul Francis, Dave Crocker, Bob Gilligan, Bill
   Simpson, Ran Atkinson, Bill Fink, Erik Nordmark, Christian Huitema,
   Sue Thompson, and Ramesh Govindan.

2. Key Issues for the Next Generation of IP

   There are several key issues that should be used in the evaluation of
   any next generation internet protocol.  Some are very
   straightforward.  For example the new protocol must be able to
   support large global internetworks.  Others are less obvious.  There
   must be a clear way to transition the current installed base of IP
   systems.  It doesn't matter how good a new protocol is if there isn't
   a practical way to transition the current operational systems running
   IPv4 to the new protocol.

2.1 Growth

   Growth is the basic issue which caused there to be a need for a next
   generation IP.  If anything is to be learned from our experience with
   IPv4 it is that the addressing and routing must be capable of
   handling reasonable scenarios of future growth.  It is important that
   we have an understanding of the past growth and where the future
   growth will come from.

   Currently IPv4 serves what could be called the computer market.  The
   computer market has been the driver of the growth of the Internet.
   It comprises the current Internet and countless other smaller
   internets which are not connected to the Internet.  Its focus is to
   connect computers together in the large business, government, and
   university education markets.  This market has been growing at an
   exponential rate.  One measure of this is that the number of networks
   in current Internet (23,494 as of 1/28/94) is doubling approximately
   every 12 months.  The computers which are used at the endpoints of
   internet communications range from PC's to Supercomputers.  Most are
   attached to Local Area Networks (LANs) and the vast majority are not
   mobile.

   The next phase of growth will probably not be driven by the computer
   market.  While the computer market will continue to grow at
   significant rates due to expansion into other areas such as schools
   (elementary through high school) and small businesses, it is doubtful
   it will continue to grow at an exponential rate.  What is likely to
   happen is that other kinds of markets will develop.  These markets
   will fall into several areas.  They all have the characteristic that
   they are extremely large.  They also bring with them a new set of
   requirements which were not as evident in the early stages of IPv4
   deployment.  The new markets are also likely to happen in parallel
   with other.  It may turn out that we will look back on the last ten
   years of Internet growth as the time when the Internet was small and
   only doubling every year.  The challenge for an IPng is to provide a
   solution which solves todays problems and is attractive in these
   emerging markets.

   Nomadic personal computing devices seem certain to become ubiquitous
   as their prices drop and their capabilities increase.  A key
   capability is that they will be networked.  Unlike the majority of
   todays networked computers they will support a variety of types of
   network attachments.  When disconnected they will use RF wireless
   networks, when used in networked facilities they will use infrared
   attachment, and when docked they will use physical wires.  This makes
   them an ideal candidate for internetworking technology as they will
   need a common protocol which can work over a variety of physical
   networks.  These types of devices will become consumer devices and
   will replace the current generation of cellular phones, pagers, and
   personal digital assistants.  In addition to the obvious requirement
   of an internet protocol which can support large scale routing and
   addressing, they will require an internet protocol which imposes a
   low overhead and supports auto configuration and mobility as a basic
   element.  The nature of nomadic computing requires an internet
   protocol to have built in authentication and confidentiality.  It
   also goes without saying that these devices will need to communicate
   with the current generation of computers.  The requirement for low
   overhead comes from the wireless media.  Unlike LAN's which will be
   very high speed, the wireless media will be several orders of
   magnitude slower due to constraints on available frequencies,
   spectrum allocation, and power consumption.

   Another market is networked entertainment.  The first signs of this
   emerging market are the proposals being discussed for 500 channels of
   television, video on demand, etc.  This is clearly a consumer market.
   The possibility is that every television set will become an Internet
   host.  As the world of digital high definition television approaches,
   the differences between a computer and a television will diminish.
   As in the previous market, this market will require an Internet
   protocol which supports large scale routing and addressing, and auto
   configuration.  This market also requires a protocol suite which
   imposes the minimum overhead to get the job done.  Cost will be the
   major factor in the selection of a technology to use.

   Another market which could use the next generation IP is device
   control.  This consists of the control of everyday devices such as
   lighting equipment, heating and cooling equipment, motors, and other
   types of equipment which are currently controlled via analog switches
   and in aggregate consume considerable amounts of power.  The size of
   this market is enormous and requires solutions which are simple,
   robust, easy to use, and very low cost.

   The challenge for the IETF in the selection of an IPng is to pick a
   protocol which meets today's requirements and also matches the
   requirements of these emerging markets.  These markets will happen
   with or without an IETF IPng.  If the IETF IPng is a good match for
   these new markets it is likely to be used.  If not, these markets
   will develop something else.  They will not wait for an IETF
   solution.  If this should happen it is probable that because of the
   size and scale of the new markets the IETF protocol would be
   supplanted.  If the IETF IPng is not appropriate for use in these
   markets, it is also probable that they will each develop their own
   protocols, perhaps proprietary.  These new protocols would not
   interoperate with each other.  The opportunity for the IETF is to
   select an IPng which has a reasonable chance to be used in these
   emerging markets.  This would have the very desirable outcome of
   creating an immense, interoperable, world-wide information
   infrastructure created with open protocols.  The alternative is a
   world of disjoint networks with protocols controlled by individual
   vendors.

2.2. Transition

   At some point in the next three to seven years the Internet will
   require a deployed new version of the Internet protocol.  Two factors
   are driving this: routing and addressing.  Global internet routing
   based on the on 32-bit addresses of IPv4 is becoming increasingly
   strained.  IPv4 address do not provide enough flexibility to
   construct efficient hierarchies which can be aggregated.  The
   deployment of Classless Inter-Domain Routing [CIDR] is extending the
   life time of IPv4 routing routing by a number of years, the effort to
   manage the routing will continue to increase.  Even if the IPv4
   routing can be scaled to support a full IPv4 Internet, the Internet
   will eventually run out of network numbers.  There is no question
   that an IPng is needed, but only a question of when.

   The challenge for an IPng is for its transition to be complete before
   IPv4 routing and addressing break.  The transition will be much
   easier if IPv4 address are still globally unique.  The two transition
   requirements which are the most important are flexibility of
   deployment and the ability for IPv4 hosts to communicate with IPng
   hosts.  There will be IPng-only hosts, just as there will be IPv4-
   only hosts.  The capability must exist for IPng-only hosts to
   communicate with IPv4-only hosts globally while IPv4 addresses are
   globally unique.

   The deployment strategy for an IPng must be as flexible as possible.
   The Internet is too large for any kind of controlled rollout to be
   successful.  The importance of flexibility in an IPng and the need
   for interoperability between IPv4 and IPng was well stated in a
   message to the sipp mailing list by Bill Fink, who is responsible for
   a portion of NASA's operational internet.  In his message he said:

      "Being a network manager and thereby representing the interests of
      a significant number of users, from my perspective it's safe to
      say that the transition and interoperation aspects of any IPng is
      *the* key first element, without which any other significant
      advantages won't be able to be integrated into the user's network
      environment.  I also don't think it wise to think of the
      transition as just a painful phase we'll have to endure en route
      to a pure IPng environment, since the transition/coexistence
      period undoubtedly will last at least a decade and may very well
      continue for the entire lifetime of IPng, until it's replaced with
      IPngng and a new transition.  I might wish it was otherwise but I
      fear they are facts of life given the immense installed base.

      "Given this situation, and the reality that it won't be feasible
      to coordinate all the infrastructure changes even at the national
      and regional levels, it is imperative that the transition
      capabilities support the ability to deploy the IPng in the
      piecemeal fashion...  with no requirement to need to coordinate
      local changes with other changes elsewhere in the Internet...

      "I realize that support for the transition and coexistence
      capabilities may be a major part of the IPng effort and may cause
      some headaches for the designers and developers, but I think it is
      a duty that can't be shirked and the necessary price that must be
      paid to provide as seamless an environment as possible to the end
      user and his basic network services such as e-mail, ftp, gopher,
      X-Window clients, etc...

      "The bottom line for me is that we must have interoperability
      during the extended transition period for the base IPv4
      functionality..."

   Another way to think about the requirement for compatibility with
   IPv4 is to look at other product areas.  In the product world,
   backwards compatability is very important.  Vendors who do not
   provide backward compatibility for their customers usually find they
   do not have many customers left.  For example, chip makers put
   considerable effort into making sure that new versions of their
   processor always run all of the software that ran on the previous
   model.  It is unlikely that Intel would develop a new processor in
   the X86 family that did not run DOS and the tens of thousands of
   applications which run on the current versions of X86's.

   Operating system vendors go to great lengths to make sure new
   versions of their operating systems are binary compatible with their
   old version.  For example the labels on most PC or MAC software
   usually indicate that they require OS version XX or greater.  It
   would be foolish for Microsoft come out with a new version of Windows
   which did not run the applications which ran on the previous version.
   Microsoft even provides the ability for windows applications to run
   on their new OS NT.  This is an important feature.  They understand
   that it was very important to make sure that the applications which
   run on Windows also run on NT.

   The same requirement is also true for IPng.  The Internet has a large
   installed base.  Features need to be designed into an IPng to make
   the transition as easy as possible.  As with processors and operating
   systems, it must be backwards compatible with IPv4.  Other protocols
   have tried to replace TCP/IP, for example XTP and OSI.  One element
   in their failure to reach widespread acceptance was that neither had
   any transition strategy other than running in parallel (sometimes
   called dual stack).  New features alone are not adequate to motivate
   users to deploy new protocols.  IPng must have a great transition
   strategy and new features.

3. History of the SIPP Effort

   The SIPP working group represents the evolution of three different
   IETF working groups focused on developing an IPng.  The first was
   called IP Address Encapsulation (IPAE) and was chaired by Dave
   Crocker and Robert Hinden.  It proposed extensions to IPv4 which
   would carry larger addresses.  Much of its work was focused on
   developing transition mechanisms.

   Somewhat later Steve Deering proposed a new protocol evolved from
   IPv4 called the Simple Internet Protocol (SIP).  A working group was
   formed to work on this proposal which was chaired by Steve Deering
   and Christian Huitema.  SIP had 64-bit addresses, a simplified
   header, and options in separate extension headers.  After lengthly
   interaction between the two working groups and the realization that
   IPAE and SIP had a number of common elements and the transition
   mechanisms developed for IPAE would apply to SIP, the groups decided
   to merge and concentrate their efforts.  The chairs of the new SIP
   working group were Steve Deering and Robert Hinden.

   In parallel to SIP, Paul Francis (formerly Paul Tsuchiya) had founded
   a working group to develop the "P" Internet Protocol (Pip).  Pip was
   a new internet protocol based on a new architecture.  The motivation
   behind Pip was that the opportunity for introducing a new internet
   protocol does not come very often and given that opportunity
   important new features should be introduced.  Pip supported variable
   length addressing in 16-bit units, separation of addresses from
   identifiers, support for provider selection, mobility, and efficient
   forwarding.  It included a transition scheme similar to IPAE.

   After considerable discussion among the leaders of the Pip and SIP
   working groups, they came to realize that the advanced features in
   Pip could be accomplished in SIP without changing the base SIP
   protocol as well as keeping the IPAE transition mechanisms.  In
   essence it was possible to keep the best features of each protocol.
   Based on this the groups decided to merge their efforts.  The new
   protocol was called Simple Internet Protocol Plus (SIPP).  The chairs
   of the merged working group are Steve Deering, Paul Francis, and
   Robert Hinden.

4. SIPP Overview

   SIPP is a new version of the Internet Protocol, designed as a
   successor to IP version 4 [IPV4].  SIPP is assigned IP version number
   6.

   SIPP was designed to take an evolutionary step from IPv4.  It was not
   a design goal to take a radical step away from IPv4.  Functions which
   work in IPv4 were kept in SIPP.  Functions which didn't work were
   removed.  The changes from IPv4 to SIPP fall primarily into the
   following categories:

      o  Expanded Routing and Addressing Capabilities

        SIPP increases the IP address size from 32 bits to 64 bits, to
        support more levels of addressing hierarchy and a much greater
        number of addressable nodes.  SIPP addressing can be further
        extended, in units of 64 bits, by a facility equivalent to
        IPv4's Loose Source and Record Route option, in combination
        with a new address type called "cluster addresses" which
        identify topological regions rather than individual nodes.
        The scaleability of multicast routing is improved by adding
        a "scope" field to multicast addresses.

     o Header Format Simplification

        Some IPv4 header fields have been dropped or made optional, to
        reduce the common-case processing cost of packet handling and to
        keep the bandwidth cost of the SIPP header almost as low as that
        of IPv4, despite the increased size of the addresses.  The basic
        SIPP header is only four bytes longer than IPv4.

     o Improved Support for Options

        Changes in the way IP header options are encoded allows for more
        efficient forwarding, less stringent limits on the length of
        options, and greater flexibility for introducing new options in
        the future.

     o Quality-of-Service Capabilities

        A new capability is added to enable the labeling of packets
        belonging to particular traffic "flows" for which the sender
        requests special handling, such as non-default quality of
        service or "real-time" service.

     o Authentication and Privacy Capabilities

        SIPP includes the definition of extensions which provide support
        for authentication, data integrity, and confidentiality.  This
        is included as a basic element of SIPP.

   The SIPP protocol consists of two parts, the basic SIPP header and
   SIPP Options.

4.1  SIPP Header Format

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version|                       Flow Label                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Payload Length        |  Payload Type |   Hop Limit   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                         Source Address                        +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                      Destination Address                      +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Version              4-bit Internet Protocol version number = 6.

      Flow Label           28-bit field.  See SIPP Quality of Service
                           section.

      Payload Length       16-bit unsigned integer.  Length of payload,
                           i.e., the rest of the packet following the
                           SIPP header, in octets.

      Payload Type         8-bit selector.  Identifies the type of
                           header immediately following the SIPP
                           header.  Uses the same values as the IPv4
                           Protocol field [STD 2, RFC 1700].

      Hop Limit            8-bit unsigned integer.  Decremented by 1
                           by each node that forwards the packet.
                           The packet is discarded if Hop Limit is
                           decremented to zero.

      Source Address       64 bits.  An address of the initial sender of
                           the packet.  See [ROUT] for details.

      Destination Address  64 bits.  An address of the intended
                           recipient of the packet (possibly not the
                           ultimate recipient, if an optional Routing
                           Header is present).

4.2 SIPP Options

   SIPP includes an improved option mechanism over IPv4.  SIPP options
   are placed in separate headers that are located between the SIPP
   header and the transport-layer header in a packet.  Most SIPP option
   headers are not examined or processed by any router along a packet's
   delivery path until it arrives at its final destination.  This
   facilitates a major improvement in router performance for packets
   containing options. In IPv4 the presence of any options requires the
   router to examine all options.  The other improvement is that unlike
   IPv4, SIPP options can be of arbitrary length and the total amount of
   options carried in a packet is not limited to 40 bytes.  This feature
   plus the manner in which they are processed, permits SIPP options to
   be used for functions which were not practical in IPv4.  A good
   example of this is the SIPP Authentication and Security Encapsulation
   options.

   In order to improve the performance when handling subsequent option
   headers and the transport protocol which follows, SIPP options are
   always an integer multiple of 8 octets long, in order to retain this
   alignment for subsequent headers.

   The SIPP option headers which are currently defined are:

     Option                     Function
     ---------------            ---------------------------------------
     Routing                    Extended Routing (like IPv4 loose source
                                route)
     Fragmentation              Fragmentation and Reassembly
     Authentication             Integrity and Authentication
     Security Encapsulation     Confidentiality
     Hop-by-Hop Option          Special options which require hop by hop
                                processing

4.3 SIPP Addressing

   SIPP addresses are 64-bits long and are identifiers for individual
   nodes and sets of nodes.  There are three types of SIPP addresses.
   These are unicast, cluster, and multicast.  Unicast addresses
   identify a single node.  Cluster addresses identify a group of nodes,
   that share a common address prefix, such that a packet sent to a
   cluster address will be delivered to one member of the group.
   Multicast addresses identify a group of nodes, such that a packet
   sent to a multicast address is delivered to all of the nodes in the
   group.

   SIPP supports addresses which are twice the number of bits as IPv4
   addresses.  These addresses support an address space which is four
   billion (2^^32) times the size of IPv4 addresses (2^^32).  Another
   way to say this is that SIPP supports four billion internets each the
   size of the maximum IPv4 internet.  That is enough to allow each
   person on the planet to have their own internet.  Even with several
   layers of hierarchy (with assignment utilization similar to IPv4)
   this would allow for each person on the planet to have their own
   internet each holding several thousand hosts.

   In addition, SIPP supports extended addresses using the routing
   option.  This capability allows the address space to grow to 128-
   bits, 192-bits (or even larger) while still keeping the address units
   in manageable 64-bit units.  This permits the addresses to grow while
   keeping the routing algorithms efficient because they continue to
   operate using 64- bit units.

4.3.1 Unicast Addresses

   There are several forms of unicast address assignment in SIPP. These
   are global hierarchical unicast addresses, local-use addresses, and
   IPv4- only host addresses.  The assignment plan for unicast addresses
   is described in [ADDR].

4.3.1.1 Global Unicast Addresses

   Global unicast addresses are used for global communication.  They are
   the most common SIPP address and are similar in function to IPv4
   addresses.  Their format is:

     |1|      n bits       |        m bits       |   p bits  | 63-n-m-p|
     +-+-------------------+---------------------+-----------+---------+
     |C|    PROVIDER ID    |    SUBSCRIBER ID    | SUBNET ID | NODE ID |
     +-+-------------------+---------------------+-----------+---------+

   The first bit is the IPv4 compatibility bit, or C-bit.  It indicates
   whether the node represented by the address is IPv4 or SIPP.  SIPP
   addresses are provider-oriented.  That is, the high-order part of the
   address is assigned to internet service providers, which then assign
   portions of the address space to subscribers, etc.  This usage is
   similar to assignment of IP addresses under CIDR.  The SUBSCRIBER ID
   distinguishes among multiple subscribers attached to the provider
   identified by the PROVIDER ID.  The SUBNET ID identifies a
   topologically connected group of nodes within the subscriber network
   identified by the subscriber prefix.  The NODE ID identifies a single
   node among the group of nodes identified by the subnet prefix.

4.3.1.2 Local-Use Address

   A local-use address is a unicast address that has only local
   routability scope (within the subnet or within a subscriber network),
   and may have local or global uniqueness scope.  They are intended for
   use inside of a site for "plug and play" local communication, for
   bootstrapping up to a single global addresses, and as part of an
   address sequence for global communication.  Their format is:

     | 4  |
     |bits|    12 bits    |                 48 bits                    |
     +----+---------------+--------------------------------------------+
     |0110|   SUBNET ID   |                 NODE ID                    |
     +----+---------------+--------------------------------------------+

   The NODE ID is an identifier which much be unique in the domain in
   which it is being used.  In most cases these will use a node's IEEE-
   802 48bit address.  The SUBNET ID identifies a specific subnet in a
   site.  The combination of the SUBNET ID and the NODE ID to form a
   local use address allows a large private internet to be constructed
   without any other address allocation.

   Local-use addresses have two primary benefits.  First, for sites or
   organizations that are not (yet) connected to the global Internet,
   there is no need to request an address prefix from the global
   Internet address space.  Local-use addresses can be used instead.  If
   the organization connects to the global Internet, it can use it's
   local use addresses to communicate with a server (e.g., using the
   Dynamic Host Configuration Protocol [DHCP]) to have a global address
   automatically assigned.

   The second benefit of local-use addresses is that they can hold much
   larger NODE IDs, which makes possible a very simple form of auto-
   configuration of addresses.  In particular, a node may discover a
   SUBNET ID by listening to a Router Advertisement messages on its
   attached link(s), and then fabricating a SIPP address for itself by
   using its link-level address as the NODE ID on that subnet.

   An auto-configured local-use address may be used by a node as its own
   identification for communication within the local domain, possibly
   including communication with a local address server to obtain a
   global SIPP address.  The details of host auto-configuration are
   described in [DHCP].

4.3.1.3 IPv4-Only Addresses

   SIPP unicast addresses are assigned to IPv4-only hosts as part of the
   IPAE scheme for transition from IPv4 to SIPP.  Such addresses have
   the following form:

     |1|            31 bits           |             32 bits            |
     +-+------------------------------+--------------------------------+
     |1|   HIGHER-ORDER SIPP PREFIX   |          IPv4 ADDRESS          |
     +-+------------------------------+--------------------------------+

   The highest-order bit of a SIPP address is called the IPv4
   compatibility bit or the C bit. A C bit value of 1 identifies an
   address as belonging to an IPv4-only node.

   The IPv4 node's 32-bit IPv4 address is carried in the low-order 32
   bits of the SIPP address.  The remaining 31 bits are used to carry
   HIGHER- ORDER SIPP PREFIX, such as a service-provider ID.

4.3.2  Cluster Addresses

   Cluster addresses are unicast addresses that are used to reach the
   "nearest" one (according to unicast routing's notion of nearest) of
   the set of boundary routers of a cluster of nodes identified by a
   common prefix in the SIPP unicast routing hierarchy.  These are used
   to identify a set of nodes.  The cluster address, when used as part
   of an address sequence, permits a node to select which of several
   providers it wants to carry its traffic.  A cluster address can only
   be used as a destination address.  In this example there would be a
   cluster address for each provider.  This capability is sometimes
   called "source selected policies".  Cluster addresses have the
   general form:

     |              n bits             |           64-n bits           |
     +---------------------------------+-------------------------------+
     |          CLUSTER PREFIX         |0000000000000000000000000000000|
     +---------------------------------+-------------------------------+

4.3.3  Multicast Addresses

   A SIPP multicast address is an identifier for a group of nodes.  A
   node may belong to any number of multicast groups.  Multicast
   addresses have the following format:


     |1|   7   |  4 |  4 |                  48 bits                    |
     +-+-------+----+----+---------------------------------------------+
     |C|1111111|FLGS|SCOP|                  GROUP ID                   |
     +-+-------+----+----+---------------------------------------------+

   Where:

     C = IPv4 compatibility bit.

     1111111 in the rest of the first octet identifies the address as
     being a multicast address.

                                   +-+-+-+-+
     FLGS is a set of 4 flags:     |0|0|0|T|
                                   +-+-+-+-+

     The high-order 3 flags are reserved, and must be initialized to 0.

     T = 0 indicates a permanently-assigned ("well-known") multicast
           address, assigned by the global internet numbering authority.

     T = 1 indicates a non-permanently-assigned ("transient") multicast
           address.

     SCOP is a 4-bit multicast scope value used to limit the scope of
     the multicast group.  The values are:

        0  reserved                  8  intra-organization scope
        1  intra-node scope          9  (unassigned)
        2  intra-link scope          10  (unassigned)
        3  (unassigned)              11  intra-community scope
        4  (unassigned)              12  (unassigned)
        5  intra-site scope          13  (unassigned)
        6  (unassigned)              14  global scope
        7  (unassigned)              15  reserved

     GROUP ID identifies the multicast group, either permanent or
     transient, within the given scope.

4.4 SIPP Routing

   Routing in SIPP is almost identical to IPv4 routing under CIDR except
   that the addresses are 64-bit SIPP addresses instead of 32-bit IPv4
   addresses.  This is true even when extended addresses are being used.
   With very straightforward extensions, all of IPv4's routing
   algorithms (OSPF, BGP, RIP, IDRP, etc.) can used to route SIPP [OSPF]
   [RIP2] [IDRP].

   SIPP also includes simple routing extensions which support powerful
   new routing functionality.  These capabilities include:

        Provider Selection (based on policy, performance, cost, etc.)
        Host Mobility (route to current location)
        Auto-Readdressing (route to new address)
        Extended Addressing (route to "sub-cloud")

   The new routing functionality is obtained by creating sequences of
   SIPP addresses using the SIPP Routing option.  The routing option is
   used by a SIPP source to list one or more intermediate nodes (or
   topological clusters) to be "visited" on the way to a packet's
   destination.  This function is very similar in function to IPv4's
   Loose Source and Record Route option.  A node would publish its
   address sequence in the Domain Name System [DNS].

   The identification of a specific transport connection is done by only
   using the first (source) and last (destination) address in the
   sequence.  These identifying addresses (i.e., first and last
   addresses of a route sequence) are required to be unique within the
   scope over which they are used.  This permits the middle addresses in
   the address sequence to change (in the cases of mobility, provider
   changes, site readdressing, etc.) without disrupting the transport
   connection.

   In order to make address sequences a general function, SIPP hosts are
   required to reverse routes in a packet it receives containing address
   sequences in order to return the packet to its originator.  This
   approach is taken to make SIPP host implementations from the start
   support the handling and reversal of source routes.  This is the key
   for allowing them to work with hosts which implement the new features
   such as provider selection or extended addresses.

   Three examples show how the extended addressing can be used.  In
   these examples, address sequences are shown by a list of individual
   addresses separated by commas.  For example:

       SRC, I1, I2, I3, DST

   Where the first address is the source address, the last address is
   the destination address, and the middle addresses are intermediate
   addresses.

   For these examples assume that two hosts, H1 and H2 wish to
   communicate.  Assume that H1 and H2's sites are both connected to
   providers P1 and P2.  A third wireless provider, PR, is connected to
   both providers P1 and P2.

                           ----- P1 ------
                          /       |       \
                         /        |        \
                       H1        PR        H2
                         \        |        /
                          \       |       /
                           ----- P2 ------

   The simplest case (no use of address sequences) is when H1 wants to
   send a packet to H2 containing the addresses:

           H1, H2

   When H2 replied it would reverse the addresses and construct a packet
   containing the addresses:

           H2, H1

   In this example either provider could be used, and H1 and H2 would
   not be able to select which provider traffic would be sent to and
   received from.

   If H1 decides that it wants to enforce a policy that all
   communication to/from H2 can only use provider P1, it would construct
   a packet containing the address sequence:

           H1, P1, H2

   This ensures that when H2 replies to H1, it will reverse the route
   and the reply it would also travel over P1.  The addresses in H2's
   reply would look like:

           H2, P1, H1

   If H1 became mobile and moved to provider PR, it could maintain (not
   breaking any transport connections) communication with H2, by sending
   packets that contain the address sequence:

           H1, PR, P1, H2

   This would ensure that when H2 replied it would enforce H1's policy
   of exclusive use of provider P1 and send the packet to H1 new
   location on provider PR.  The reversed address sequence would be:

           H2, P1, PR, H1

   The address extension facility of SIPP can be used for provider
   selection, mobility, readdressing, and extended addressing.  It is a
   simple but powerful capability.

4.5 SIPP Quality-of-Service Capabilities

   The Flow Label field in the SIPP header may be used by a host to
   label those packets for which it requests special handling by SIPP
   routers, such as non-default quality of service or "real-time"
   service.  This labeling is important in order to support applications
   which require some degree of consistent throughput, delay, and/or
   jitter.  The Flow Label is a 28-bit field, internally structured into
   three subfields as follows:

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |R|  DP |                    Flow ID                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     R (Reserved)       1-bit subfield.  Initialized to zero for
                        transmission; Ignored on reception.

     DP (Drop Priority) 3-bit unsigned integer.  Specifies the
                        priority of the packet, relative to other
                        packets from the same source, for being
                        discarded by a router under conditions of
                        congestion.  Larger values indicates a
                        greater willingness by the sender to allow
                        the packet to be discarded.

     Flow ID            24-bit subfield used to identify a
                        specific flow.

   A flow is a sequence of packets sent from a particular source to a
   particular (unicast or multicast) destination for which the source
   desires special handling by the intervening routers.  There may be
   multiple active flows from a source to a destination, as well as
   traffic that is not associated with any flow.  A flow is identified
   by the combination of a Source Address and a non-zero Flow ID.
   Packets that do not belong to a flow carry a Flow ID of zero.

   A Flow ID is assigned to a flow by the flow's source node.  New Flow
   IDs must be chosen (pseudo-)randomly and uniformly from the range 1
   to FFFFFF hex.  The purpose of the random allocation is to make any
   set of bits within the Flow ID suitable for use as a hash key by the
   routers, for looking up the special-handling state associated with
   the flow.  A Flow ID must not be re-used by a source for a new flow
   while any state associated with the previous usage still exists in
   any router.

   The Drop Priority subfield provides a means separate from the Flow ID
   for distinguishing among packets from the same source, to allow a
   source to specify which of its packets are to be discarded in
   preference to others when a router cannot forward them all.  This is
   useful for applications like video where it is preferable to drop
   packets carrying screen updates rather than the packets carrying the
   video synchronization information.

4.6 SIPP Security

   The current Internet has a number of security problems and lacks
   effective privacy and authentication mechanisms below the application
   layer.  SIPP remedies these shortcomings by having two integrated
   options that provide security services.  These two options may be
   used singly or together to provide differing levels of security to
   different users.  This is very important because different user
   communities have different security needs.

   The first mechanism, called the "SIPP Authentication Header", is an
   option which provides authentication and integrity (without
   confidentiality) to SIPP datagrams.  While the option is algorithm-
   independent and will support many different authentication
   techniques, the use of keyed MD5 is proposed to help ensure
   interoperability within the worldwide Internet.  This can be used to
   eliminate a significant class of network attacks, including host
   masquerading attacks.  The use of the SIPP Authentication Header is
   particularly important when source routing is used with SIPP because
   of the known risks in IP source routing.  Its placement at the
   internet layer can help provide host origin authentication to those
   upper layer protocols and services that currently lack meaningful
   protections.  This mechanism should be exportable by vendors in the
   United States and other countries with similar export restrictions
   because it only provides authentication and integrity, and
   specifically does not provide confidentiality.  The exportability of
   the SIPP Authentication Header encourages its widespread
   implementation and use.

   The second security option provided with SIPP is the "SIPP
   Encapsulating Security Header".  This mechanism provides integrity
   and confidentiality to SIPP datagrams.  It is simpler than some
   similar security protocols (e.g., SP3D, ISO NLSP) but remains
   flexible and algorithm-independent.  To achieve interoperability
   within the global Internet, the use of DES CBC is proposed as the
   standard algorithm for use with the SIPP Encapsulating Security
   Header.

5. SIPP Transition Mechanisms

   The two key motivations in the SIPP transition mechanisms are to
   provide direct interoperability between IPv4 and SIPP hosts and to
   allow the user population to adopt SIPP in an a highly diffuse
   fashion.  The transition must be incremental, with few or no critical
   interdependencies, if it is to succeed.  The SIPP transition allows
   the users to upgrade their hosts to SIPP, and the network operators
   to deploy SIPP in routers, with very little coordination between the
   two.

   The mechanisms and policies of the SIPP transition are called "IPAE".
   Having a separate term serves to highlight those features designed
   specifically for transition.  Once an acronym for an encapsulation
   technique to facilitate transition, the term "IPAE" now is mostly
   historical.

   The IPAE transition is based on five key elements:

    1) A 64-bit SIPP addressing plan that encompasses the existing
       32-bit IPv4 addressing plan.  The 64-bit plan will be used to
       assign addresses for both SIPP and IPv4 nodes at the beginning
       of the transition.  Existing IPv4 nodes will not need to change
       their addresses, and IPv4 hosts being upgraded to SIPP keep their
       existing IPv4 addresses as the low-order 32 bits of their SIPP
       addresses.  Since the SIPP addressing plan is a superset of the
       existing IPv4 plan, SIPP hosts are assigned only a single 64-bit
       address, which can be used to communicate with both SIPP and IPv4
       hosts.

    2) A mechanism for encapsulating SIPP traffic within IPv4 packets so
       that the IPv4 infrastructure can be leveraged early in the
       transition.  Most of the "SIPP within IPv4 tunnels" can be
       automatically configured.

    3) Algorithms in SIPP hosts that allow them to directly interoperate
       with IPv4 hosts located on the same subnet and elsewhere in the
       Internet.

    4) A mechanism for translating between IPv4 and SIPP headers to
       allow SIPP-only hosts to communicate with IPv4-only hosts and to
       facilitate IPv4 hosts communicating over over a SIPP-only
       backbone.

    5) An optional mechanism for mapping IPv4 addresses to SIPP address
       to allow improved scaling of IPv4 routing.  At the present time
       given the success of CIDR, this does not look like it will be
       needed in a transition to SIPP.  If Internet growth should
       continue beyond what CIDR can handle, it is available as an
       optional mechanism.

   IPAE ensures that SIPP hosts can interoperate with IPv4 hosts
   anywhere in the Internet up until the time when IPv4 addresses run
   out, and afterward allows SIPP and IPv4 hosts within a limited scope
   to interoperate indefinitely.  This feature protects for a very long
   time the huge investment users have made in IPv4.  Hosts that need
   only a limited connectivity range (e.g., printers) need never be
   upgraded to SIPP.  This feature also allows SIPP-only hosts to
   interoperate with IPv4-only hosts.

   The incremental upgrade features of IPAE allow the host and router
   vendors to integrate SIPP into their product lines at their own pace,
   and allows the end users and network operators to deploy SIPP on
   their own schedules.

   The interoperability between SIPP and IPv4 provided by IPAE also has
   the benefit of extending the lifetime of IPv4 hosts.  Given the large
   installed base of IPv4, changes to IPv4 in hosts are nearly
   impossible.  Once an IPng is chosen, most of the new feature
   development will be done on IPng.  New features in IPng will increase
   the incentives to adopt and deploy it.

6. Why SIPP?

   There are a number of reasons why SIPP should be selected as the
   IETF's IPng.  It solves the Internet scaling problem, provides a
   flexible transition mechanism for the current Internet, and was
   designed to meet the needs of new markets such as nomadic personal
   computing devices, networked entertainment, and device control.  It
   does this in a evolutionary way which reduces the risk of
   architectural problems.

   Ease of transition is a key point in the design of SIPP.  It is not
   something was was added in at the end.  SIPP is designed to
   interoperate with IPv4.  Specific mechanisms (C-bit, embedded IPv4
   addresses, etc.) were built into SIPP to support transition and
   compatability with IPv4.  It was designed to permit a gradual and
   piecemeal deployment without any dependencies.

   SIPP supports large hierarchical addresses which will allow the
   Internet to continue to grow and provide new routing capabilities not
   built into IPv4.  It has cluster addresses which can be used for
   policy route selection and has scoped multicast addresses which
   provide improved scaleability over IPv4 multicast.  It also has local
   use addresses which provide the ability for "plug and play"
   installation.

   SIPP is designed to have performance better than IPv4 and work well
   in low bandwidth applications like wireless.  Its headers are less
   expensive to process than IPv4 and its 64-bit addresses are chosen to
   be well matched to the new generation of 64bit processors.  Its
   compact header minimizes bandwidth overhead which makes it ideal for
   wireless use.

   SIPP provides a platform for new Internet functionality.  This
   includes support for real-time flows, provider selection, host
   mobility, end-to- end security, auto-configuration, and auto-
   reconfiguration.

   In summary, SIPP is a new version of IP.  It can be installed as a
   normal software upgrade in internet devices.  It is interoperable
   with the current IPv4.  Its deployment strategy was designed to not
   have any "flag" days.  SIPP is designed to run well on high
   performance networks (e.g., ATM) and at the same time is still
   efficient for low bandwidth networks (e.g., wireless).  In addition,
   it provides a platform for new internet functionality that will be
   required in the near future.

7. Status of SIPP Effort

   There are many active participants in the SIPP working group.  Groups
   making active contributions include:

   Group                   Activity
   ---------------------   ----------------------------------------
   Beame & Whiteside       Implementation (PC)
   Bellcore                Implementation (SunOS), DNS and ICMP specs.
   Digital Equipment Corp. Implementation (Alpha/OSF, Open VMS)
   INRIA                   Implementation (BSD, BIND), DNS & OSPF specs.
   INESC                   Implementation (BSD/Mach/x-kernel)
   Intercon                Implementation (MAC)
   MCI                     Phone Conferences
   Merit                   IDRP for SIPP Specification
   Naval Research Lab.     Implementation (BSD) Security Design
   Network General         Implementation (Sniffer)
   SGI                     Implementation (IRIX, NetVisulizer)
   Sun                     Implementation (Solaris 2.x, Snoop)
   TGV                     Implementation (Open VMS)
   Xerox PARC              Protocol Design
   Bill Simpson            Implementation (KA9Q)

   As of the time this paper was written there were a number of SIPP and
   IPAE implementations.  These include:

   Implementation          Status
   --------------          ------------------------------------
   BSD/Mach                Completed (telnet, NFS, AFS, UDP)
   BSD/Net/2               In Progress
   Bind                    Code done
   DOS &Windows            Completed (telnet, ftp, tftp, ping)
   IRIX                    In progress (ping)
   KA9Q                    In progress (ping, TCP)
   Mac OS                  Completed (telnet, ftp, finger, ping)
   NetVisualizer           Completed (SIP & IPAE)
   Open VMS                Completed (telnet, ftp), In Progress
   OSF/1                   In Progress (ping, ICMP)
   Sniffer                 Completed (SIP & IPAE)
   Snoop                   Completed (SIP & IPAE)
   Solaris                 Completed (telnet, ftp, tftp, ping)
   Sun OS                  In Progress

8. Where to Get Additional Information

   The documentation listed in the reference sections can be found in
   one of the IETF internet draft directories or in the archive site for
   the SIPP working group.  This is located at:

           ftp.parc.xerox.com      in the /pub/sipp        directory.

   In addition other material relating to SIPP (such as postscript
   versions of presentations on SIPP) can also be found in the SIPP
   working group archive.

   To join the SIPP working group, send electronic mail to

           sipp-request@sunroof.eng.sun.com

   An archive of mail sent to this mailing list can be found in the IETF
   directories at cnri.reston.va.us.

9. Security Considerations

   Security issues are discussed in section 4.6.

10. Author's Address

   Robert M. Hinden
   Manager, Internet Engineering
   Sun Microsystems, Inc.
   MS MTV5-44
   2550 Garcia Ave.
   Mt. View, CA 94303

   Phone: (415) 336-2082
   Fax: (415) 336-6016
   EMail: hinden@eng.sun.com

11. References

   [ADDR]  Francis, P., "Simple Internet Protocol Plus (SIPP): Unicast
           Hierarchical Address Assignment", Work in Progress, January
           1994.

   [AUTH]  Atkinson, R., "SIPP Authentication Payload",
           Work in Progress, January, 1994.

   [CIDR]  Fuller, V., Li, T., Yu, J., and K. Varadhan, "Supernetting:
           an Address Assignment and Aggregation Strategy", RFC 1338,
           BARRNet, cisco, Merit, OARnet, June 1992.

   [DISC]  Simpson, W., "SIPP Neighbor Discovery", Work in Progress,
           March 1994.

   [DIS2]  Simpson, W., "SIPP Neighbor Discovery -- ICMP Message
           Formats", Work in Progress, March 1994.

   [DHCP]  Thomson, S., "Simple Internet Protocol Plus (SIPP): Automatic
           Host Address Assignment", Work in Progress, March 1994.

   [DNS]   Thomson, S., and C. Huitema, "DNS Extensions to Support
           Simple Internet Protocol Plus (SIPP)", Work in Progress,
           March 1994.

   [ICMP]  Govindan, R., and S. Deering, "ICMP and IGMP for the Simple
           Internet Protocol Plus (SIPP)", Work in Progress, March 1994.

   [IDRP]  Hares, S., "IDRP for SIP", Work in Progress, November 1993.

   [IPAE]  Gilligan, R., et al, "IPAE: The SIPP Interoperability and
           Transition Mechanism", Work in Progress, March 1994.

   [IPV4]  Postel, J., "Internet Protocol- DARPA Internet Program
           Protocol Specification", STD 5, RFC 791, DARPA,
           September 1981.

   [OSPF]  Francis, P., "OSPF for SIPP", Work in Progress, February
           1994.

   [RIP2]  Malkin, G., and C. Huitema, "SIP-RIP", Work in Progress,
           March 1993.

   [ROUT]  Deering, S., et al, "Simple Internet Protocol Plus (SIPP):
           Routing and Addressing", Work in Progress, February 1994.

   [SARC]  Atkinson, R., "SIPP Security Architecture", Work in Progress,
           January 1994.

   [SECR]  Atkinson, R., "SIPP Encapsulating Security Payload (ESP)",
           Work in Progress, January 1994.

   [SIPP]  Deering, S., "Simple Internet Protocol Plus (SIPP)
           Specification", Work in Progress, February 1994.