Network Working Group                                           J. Bound
Request for Comments: 1682                 Digital Equipment Corporation
Category: Informational                                      August 1994

                 IPng BSD Host Implementation Analysis

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.


   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 mailing list.


   This IPng white paper, IPng BSD Host Implementation Analysis,
   was submitted to the IPng Directorate to provide a BSD host point of
   reference to assist with the engineering considerations during the
   IETF process to select an IPng proposal.  The University of
   California Berkeley Software Distribution (BSD) TCP/IP (4.3 + 4.4)
   system implementation on a host is used as a point of reference for
   the paper.

   This document only reflects the author's personal analysis based on
   research and implementation experience for IPng, and does not
   represent any product or future product from any host vendor.  Nor
   should it be construed that it is promoting any specific IPng at this


   The author would like to acknowledge the many host implementation
   discussions and inherent knowledge gained from discussions with the
   following persons within Digital over the past year: Peter Grehan,
   Eric Rosen, Dave Oran, Jeff Mogul, Bill Duane, Tony Lauck, Bill Hawe,
   Jesse Walker, John Dustin, Alex Conta, and Fred Glover.  The author
   would also like to acknowledge like discussions from outside his
   company with Bob Hinden (SUN), Bob Gilligan (SUN), Dave Crocker
   (SGI), Dave Piscitello (Core Competence), Tracy Mallory (3Comm), Rob
   Ullmann (Lotus), Greg Minshall (Novell), J Allard (Microsoft), Ramesh
   Govinden (Bellcore), Sue Thompson (Bellcore), John Curran (NEARnet),

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RFC 1682         IPng BSD Host Implementation Analysis       August 1994

   Christian Huitema (INRIA), and Werner Volgels (INESC).  The author
   would also like to thank Digital Equipment Corporation for the
   opportunity to work on IPng within the IETF as part of his job.

1. Introduction

   A host in the context of this white paper is a system that contains
   an operating system supporting a network subsystem as one of its
   parts, and an interprocess communications facility to access that
   network subsystem.  These hosts are often referenced as a
   Workstation, Server, PC, Super Computer, Mainframe, or an Embedded
   System (Realtime Devices).

   IPng will require changes to a hosts network software architecture.
   Those changes should be as transparent as possible to the existing
   IPv4 applications executing on hosts.

   After discussing the network software architecture for a BSD host the
   paper will discuss the perceived network software alterations,
   extended capabilities, transition software, and a deployment
   consideration for IPng hosts.

   The inclusive OR of all IPng proposals was used to develop the
   engineering considerations discussed in this paper.

2. Network Software Architecture

   The BSD host network software architecture consists essentially of
   three components: the interprocess communications facility, the
   network communications subsystem, and the network protocols
   supported. These three components are tightly coupled and must be
   integrated in a way that affords high performance for the
   applications that are dependent on these components to interoperate
   efficiently.  A BSD host implementation view of the TCP/IP protocol
   suite is depicted in the following network architecture diagram.

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RFC 1682         IPng BSD Host Implementation Analysis       August 1994

   |                        Application Layer                        |
   |                                                                 |
   |                Socket and Network Library APIs                  |
   |                                                                 |
   |  BIND DNS                                                       |
   |  SNMP Management                                                |
   |                          User Space                             |
   |                         Kernel Space          AF_INET           |
   |                                        Communications Domain    |
   |  Socket Layer                                                   |
   |                                                                 |
   |                     Transport Layer TCP & UDP                   |
   |                                               Queues/Control    |
   |                                                 Blocks          |
   |                        Network Layer                            |
   |              +-----------------------------------+              |
   |              | IPv4 Modules  Discovery Multicast |              |
   |              |                ICMP       IGMP    |              |
   |              |                   Routing         |   Routing    |
   |              |                RIP        EGP     |   Tables     |
   |              |                OSPF       BGP     |              |
   |              |                I-IS-IS    IDRP    |              |
   |              +-----------------------------------+              |
   |                     Link Dependent Layer                        |
   |              +-----------------------------------+              |
   |              | ARP, RARP, InARP, NCPs, Addr Tbls |              |
   |              +-----------------------------------+              |
   |  Discovery & Interface                                          |
   |      Cache                                                      |
   |                     Data Link Layer                             |
   |              +-----------------------------------+              |
   |              | Ethernet, FDDI, ATM, HIPPI, PPP   |              |
   |              +-----------------------------------+              |

2.1 Interprocess Communications Facility

   The interprocess communications (IPC) facilities includes three
   critical parts:

      1.  The IPC mechanism to the network communications subsystem.
      2.  The ability to access a network protocol set within that
      3.  The structures supporting the network communications

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RFC 1682         IPng BSD Host Implementation Analysis       August 1994

   The IPC facility has two implementation parts.  The part in user
   space and the part in kernel space within the operating system. This
   is often not differentiated and why in the previous network
   architecture diagram you will see sockets in both user and kernel
   space.  An IPC supports in user space an application program
   interface (API) which application developers use to access the
   network communications features of the host. These APIs have
   corresponding functions in the kernel space which execute the
   functions requested by the user space requests through the APIs.

   The sockets paradigm on a BSD host defines the data structure of the
   network address within a selected protocol family (communications
   domain) in the network subsystem.  This data structure consists of an
   address family, a port for the protocol selected, and a network

   The IPC facility on a host is dependent upon its interface to the
   BIND DNS application which is the defacto method when using TCP/IP to
   retrieve network addresses.

   Other interfaces that may be required by applications to properly set
   up the network connection within the IPC facility include:
   setting/getting options for the protocols used, obtaining/accessing
   information about networks, protocols, and network services, and
   sending/transmitting datagrams.

2.2 Network Communications Subsystem

   The network communications subsystem consists of the following
   generic parts as depicted in the previous network architecture
   diagram: transport layer, network layer, link dependent layer, and
   data link layer.  These may not be implemented as true distinct
   layers on a BSD host, but they are referenced in this white paper in
   that manner for purposes of discussion.

   The transport layer supports the application interface into the
   network communications subsystem and sets up the parametric pieces to
   initiate and accept connections.  The transport layer performs these
   functions through requests to the lower layers of the network
   communications subsystem.  The transport layer also supports the
   queues and protocol control blocks for specific network connections.

   The network layer supports the modules to build and extend the
   network layer datagram, the control protocol datagrams, and the
   routing abstraction on the host.  This layer of the network
   communications subsystem on a BSD host is often extended to provide
   both interior and exterior routing functionality.

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RFC 1682         IPng BSD Host Implementation Analysis       August 1994

   The link dependent layer supports the modules that provide an
   interface for the network communications subsystem to map network
   addresses to physical addresses, and build the necessary cache so
   this information is available to the host network software.

   On a BSD host the network layer and link dependent layer together
   provide system discovery for hosts and routers.

   The data link layer supports the modules that define the structures
   for communicating with the hardware media used by the host on the
   local network.

2.3 Network Protocols

   The TCP/IP protocol suite as defined by the IETF RFC specifications
   are the set of network protocols used by this white paper for

3. Network Software Alterations

   The IPng network software alterations to a BSD host perceived at this
   time are as follows:

      1.  Applications Embedding IPv4 Addresses.
      2.  Transport Interfaces and Network APIs.
      3.  Socket Layer and Structures.
      4.  Transport Layer.
      5.  Network Layer Components.
      6.  Link dependent Layer.

3.1 Applications Embedding IPv4 Addresses

   Internet style applications in this white paper are the set of
   protocols defined for an end user using TCP/IP to exchange messages,
   transfer files, and establish remote login sessions.

   Applications use the sockets network APIs to maintain an opaque view
   of the network addresses used to support connections across a
   network. Opaque in this context means that the application determines
   the network address for the connection and then binds that address to
   a socket.  The application then uses the reference defined for that
   socket to receive and transmit data across a network.

   An application that embeds an IPv4 network address within its
   datagram has made an underlying assumption that the format of that
   address is permanent.  This will cause a great problem when IPng
   causes addresses to change.  Thus far only one Internet style
   application has been determined to cause this problem and that is FTP

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RFC 1682         IPng BSD Host Implementation Analysis       August 1994


3.2 Transport Interfaces and Network APIs

   The transport interface and network API enhancements that must take
   place on a BSD host because of IPng are alterations that affect the
   size of the network address used by the socket data structure.
   Depending on how this is implemented on the host, supporting both
   IPv4 and IPng could require existing IPv4 applications to be
   recompiled.  In the worst case it could require modifications to the
   existing IPv4 applications software that accesses the network
   communications subsystem.

   There will have to be enhancements to the network APIs that an
   application uses to retrieve BIND DNS records to differentiate
   between IPv4 and IPng address requests.

   The network API enhancements and how they are implemented will affect
   the capability of any IPng proposal on a BSD host to be able to
   interoperate between an IPv4 only, an IPng only, and an IPng-IPv4
   host system.

   Depending on the IPng proposal selected the network options,
   services, and management objects will have to be extended at the
   transport interface so those features can be accessed by applications

3.3 Socket Layer and Structures

   The socket layer and structures will require changes to support any
   IPng proposals network address.  In addition new or removed options
   and services will need to be incorporated into the socket abstraction
   within the network communications subsystem.

3.4 Transport Layer

   The transport layer will need to be modified to support any new or
   removed services proposed by an IPng solution set.  The transport
   layer will become more overloaded to support the binding of either
   the IPv4 or IPng network layer components to differentiate the
   services and structures available to a host application.  The
   overload will also take place to support functionality removed in the
   network layer and moved to the transport layer if proposed by an IPng

   It will also take some design thought to implement IPng so the
   hundreds of man years invested in performance improvements in the
   host transport layer are maintained.   This must be analyzed in depth

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RFC 1682         IPng BSD Host Implementation Analysis       August 1994

   and should be part of the operational testing of any IPng proposal.

3.5 Network Layer Components

   The network layer components for IPng will require the greatest
   alterations on a host.  In addition a host will be required to
   maintain an integrated network layer below the transport layer
   software to support either the IPng or IPv4 network layer and
   associated components.

   Depending on the IPng selected the host alterations to the network
   layer components will range from complete replacement with new
   protocols to extensions to existing IPv4 network layer protocols to
   support IPng.

   All IPng proposals will affect the BSD host routing abstraction to
   maintain host software that supports interior and exterior routing.
   Depending on the proposal selected those changes can cause either a
   complete new paradigm or an update to the existing IPv4 paradigm.

   System discovery of nodes on the local subnetwork or across an
   internetwork path in all IPng proposals will require changes to the
   BSD host software network layer component.

3.6 Link dependent Layer

   The link dependent layer on a host will need to accommodate new IPng
   addresses and the system discovery models of any IPng proposal.

4. Extended Capabilities with IPng

   Extended capabilities that could be implemented by BSD hosts are
   listed below.  Many of these capabilities exist today with IPv4, but
   may require changes with the implementation of IPng.  Some of them
   will be new capabilities.

4.1 Autoconfiguration and Autoregistration

   Today hosts can provide autoconfiguration with DHCP using IPv4
   addresses. IPng hosts will be faced with having to provide support
   for existing IPv4 addresses and the new IPng addresses.  In addition
   the boot-strap protocol BOOTP used to boot minimal BSD host
   configurations (e.g., diskless nodes) will need to be supported by
   IPng hosts.

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RFC 1682         IPng BSD Host Implementation Analysis       August 1994

4.2 PATH MTU Discovery

   PATH MTU discovery appears to be something each proposal is
   considering.  Alterations to the existing implementation of PATH MTU
   are perceived because changes are expected in system discovery.

4.3 Multicast

   Each proposal has depicted alterations to Multicast that will affect
   present BSD host implementations of IPv4 Multicast.  In addition it
   appears that the IPv4 unicast broadcast will be replaced by a
   multicast broadcast.

4.4 Flow Specification and Handling

   This will be an extended capability proposed by all IPngs'.

4.5 System Discovery

   Each proposal has depicted a new model for IPng system discovery of a

4.6 Translation and Encapsulation

   The routing abstraction in a BSD host will have to deal with the
   affect of any translation or encapsulation of network layer
   datagrams, if they are required by an IPng.

4.7 Network Layer Security

   It is perceived that network layer security will be required at the
   network layer component of IPng and this will have to be implemented
   by a BSD host.

4.8 Socket Address Structure

   The network kernel socket address structure will change because of

4.9 Network APIs

   The network APIs for a BSD host will have to be enhanced to support
   IPng.  In addition any new options available to the applications
   because of the IPng network service will have to be added as an
   option to the APIs.

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RFC 1682         IPng BSD Host Implementation Analysis       August 1994

4.10 Network Management

   Network management for IPng will have to support new network objects
   as defined by the IPng proposal.  In addition the data structures in
   the BSD host network kernel used as information to display network
   topology will be altered by a new network layer datagram and
   associated components.

5. Transition Software

   Transition software in this white paper references the network
   software alterations on a host to support both IPv4 and IPng for
   applications and the hosts operating system network kernel.  It is
   the subject of another set of papers to identify the transition
   software required by network managers to transition their users from
   IPv4 to IPng.

   Transition software on a host will be required to maintain
   compatibility between IPv4 and IPng, and to manage both the existing
   IPv4 and IPng environments as follows:

      1.  BIND DNS record updates and handling by the application.
      2.  SNMP management interface and monitoring of host network
      3.  APIs supporting IPv4 and IPng differentiation for the
      4.  Defacto network tools altered (e.g., tcpdump, traceroute,
      5.  ARP to new system discovery.
      6.  BOOTP diskless node support for IPng.
      7.  DHCP integration with IPng Autoconfiguration.
      8.  Routing table configuration on the BSD host (e.g., routed,
      9.  Selection of the network layer (IPv4 or IPng) at the
          transport layer.
      10.  New options and services provided by an IPng protocol.
      11.  IPv4 and IPng routing protocols in the network layer.
      12.  IPv4 and IPng system discovery in the network layer.

   These are only the highlights of the transition software that a host
   will have to deal with in its implementation of IPng.  The host
   network architecture diagram depicted previously will require
   software enhancements to each label in the diagram.

   It is very important that each IPng proposal provide a specification
   for a transition plan from IPv4 to IPng and their technical criteria
   for the interoperation between IPv4 and IPng.

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RFC 1682         IPng BSD Host Implementation Analysis       August 1994

   It should also be a requirement that existing IPv4 applications not
   have to be recompiled when a host has implemented both an IPv4 and an
   IPng network layer and associated components.

   It is very desirable that when a host implements both an IPv4 and an
   IPng network layer and associated components that there is no
   performance degradation on the host compared to the performance of an
   existing IPv4 only host.

   It should not be a requirement by IPng that a host must support both
   an IPv4 and an IPng network layer.

6. A Deployment Consideration

   Complete and extensive technical specifications must be available for
   any IPng proposal, and a selection of any proposal must accommodate
   multiple implementations. The IPng Directorate should review proposed
   specifications for completeness.

   It is important that the IPng Directorate determine how long the CIDR
   IPv4 address plan can extend the life of IPv4 addresses on the
   Internet.  This variable can affect the time we have to deploy IPng
   and the proposed transition plans.


   [1] Gilligan, B., et. al., "IPAE: The SIPP Interoperability and
       Transition Mechanism", Work in Progress.

   [2] Piscitello, D., "FTP Operation Over Big Address Records
       (FOOBAR)", RFC 1639, Core Competence, Inc., June 1994.

Security Considerations

   Security issues are discussed in Section 4.7.

Author's Address

   Jim Bound
   Digital Equipment Corporation
   110 Spitbrook Road ZK3-3/U14
   Nashua, NH 03062-2698

   Phone: +1 603 881 0400

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