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rfc:rfc1710

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

Hinden [Page 1] RFC 1710 SIPP IPng White Paper October 1994

 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

Hinden [Page 2] RFC 1710 SIPP IPng White Paper October 1994

 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.

Hinden [Page 3] RFC 1710 SIPP IPng White Paper October 1994

 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

Hinden [Page 4] RFC 1710 SIPP IPng White Paper October 1994

 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

Hinden [Page 5] RFC 1710 SIPP IPng White Paper October 1994

 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

Hinden [Page 6] RFC 1710 SIPP IPng White Paper October 1994

 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.

Hinden [Page 7] RFC 1710 SIPP IPng White Paper October 1994

   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.

Hinden [Page 8] RFC 1710 SIPP IPng White Paper October 1994

    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.

Hinden [Page 9] RFC 1710 SIPP IPng White Paper October 1994

 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].

Hinden [Page 10] RFC 1710 SIPP IPng White Paper October 1994

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

Hinden [Page 11] RFC 1710 SIPP IPng White Paper October 1994

 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

Hinden [Page 12] RFC 1710 SIPP IPng White Paper October 1994

 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)

Hinden [Page 13] RFC 1710 SIPP IPng White Paper October 1994

      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.

Hinden [Page 14] RFC 1710 SIPP IPng White Paper October 1994

 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.
  1. —- 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

Hinden [Page 15] RFC 1710 SIPP IPng White Paper October 1994

 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

Hinden [Page 16] RFC 1710 SIPP IPng White Paper October 1994

 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

Hinden [Page 17] RFC 1710 SIPP IPng White Paper October 1994

 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.

Hinden [Page 18] RFC 1710 SIPP IPng White Paper October 1994

  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.

Hinden [Page 19] RFC 1710 SIPP IPng White Paper October 1994

 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.

Hinden [Page 20] RFC 1710 SIPP IPng White Paper October 1994

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

Hinden [Page 21] RFC 1710 SIPP IPng White Paper October 1994

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.

Hinden [Page 22] RFC 1710 SIPP IPng White Paper October 1994

 [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.

Hinden [Page 23]

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