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.
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 big-internet@munnari.oz.au mailing list.
Overview
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
time.
Acknowledgments
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),
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.
+-----------------------------------------------------------------+
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
subsystem.
3. The structures supporting the network communications
subsystem.
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
address.
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.
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 RFCspecifications
are the set of network protocols used by this white paper for
reference.
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
[1,2].
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
software.
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
solution.
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
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.
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
host.
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
IPng.
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.
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
structures.
3. APIs supporting IPv4 and IPng differentiation for the
application.
4. Defacto network tools altered (e.g., tcpdump, traceroute,
netstat).
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,
ifconfig).
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.
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.
References
[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)", RFC1639, 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
