Network Working Group E. Britton
Request for Comments: 1678 J. Tavs
Category: Informational IBM
August 1994
IPng Requirements of Large Corporate Networks
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. This draft
summarizes some of the requirements of large corporate networks for
the next generation of the Internet protcol suite.
Executive Overview
As more and more corporations are using TCP/IP for their mission-
critical applications, they are bringing additional requirements,
summarized below, the satisfaction of which would make TCP/IP even
more appealing to businesses. Since these are requirements rather
than solutions, we include capabilities that might be provided in
protocol layers other than the one that IPv4 occupies; i.e., these
items might lie outside the scope typically envisioned for IPng, but
we'll refer to them as IPng requirements nonetheless. When we
mention potential solutions, it is not to suggest that they are the
best approach, but merely to clarify the requirement.
Among business users the major requirements we see for IPng are:
-- smooth migration from, and coexistence with, IPv4;
-- predictable levels of service for predictable costs;
-- security; and
-- accommodation of multiple protocols suites.
We also mention several more specific requirements.
IPng must have a viable strategy for migration from, and coexistence
with, IPv4. IPv4 and IPng must coexist well, because they will need
to do so for several years. To encourage IPv4 users to upgrade to
IPng, IPng must offer compelling advantages and an easy migration
path.
Corporate networks must meet promised levels of service while
controlling costs through efficient use of resources. The IETF
should consider both technical solutions (sUCh as service classes and
priorities) and administrative ones (such as accounting) to promote
economy.
Many businesses will not connect to a network until they are
confident that it will not significantly threaten the
confidentiality, integrity, or availability of their data.
Corporations tend to use multiple protocols. Numerous forces stymie
the desire to settle on just one protocol for a large corporation:
diverse installed bases, skills, technical factors, and the general
trend toward corporate decentralization. The IETF needs a strategy
for heterogeneity flexible enough to accommodate the principal
multiprotocol techniques, including multiprotocol transport,
tunneling, and link sharing.
Some of these requirements might be satisfied by more extensive
deployment of existing Internet architectures (e.g., Generic Security
Service and IPv4 type of service). The current Internet protocols
could be enhanced to satisfy most of the remaining requirements of
commercial users while retaining IPv4. Nevertheless, some
corporations will be scared away from TCP/IP by the publicity about
the address space until the IETF sets a direction for its expansion.
Migration and Coexistence
As the use of IPv4 continues to grow, the day may come when no more
IPv4 network addresses will be left, and no additional networks will
be able to connect to the Internet. Classless Inter-Domain Routing
(CIDR, RFC1519) and careful gleaning of the address space will
postpone that cutoff for several years. The hundreds of millions of
people on networks that do get IPv4 addresses won't be affected
directly by the exhaustion of the address space, but they will miss
the opportunity to communicate with those less lucky.
Because the Internet is too large for all its users to cutover to
IPng quickly, IPng must coexist well with IPv4. Furthermore, IPv4
users won't upgrade to IPng without a compelling reason. Access to
new services will not be a strong motivation, since new services will
want to support both the IPng users and the IPv4 users. Only
services that cannot exist on IPv4 will be willing to use IPng
exclusively. Moreover, if IPng requires more resources (e.g.,
storage, memory, or administrative complexity) than IPv4, users will
not install IPng unless it has clear benefits over IPv4. Indeed, the
millions of users of low-end systems (DOS, sub-notebooks) might not
ever be able to use IPng if it takes more memory. Thus there will be
a long period of coexistence between IPng and IPv4, so the
coexistence needs to be quite painless, and not based on any
assumption that IPv4 use will diminish quickly.
Service Level Agreements
If a corporation depends on its network for applications that are
critical to its business (such as airlines do for reservations, and
brokerages do for stock and bond trades), then the corporation
insists that the network provide the needed service level for a
predictable cost, so they can allow for it in their budget ahead of
time. A service level agreement (SLA) is a contract between
network's provider and users that defines the service level which a
user will see and the cost associated with that level of service.
Measurements in an SLA may include response times (average and
maximum), availability percentages, number of active sessions,
throughput rates, etc.. Businesses need to be able to predict and
guarantee the service levels and costs (routing capacity, link
bandwidth, etc.) for their traffic patterns on a TCP/IP network.
IPng should allow control of the cost of networking, a major concern
for corporations. Teleprocessing lines are a significant cost in
corporate networks. Although the cost per bit-per-second tends to be
lower on higher-bandwidth links, high-bandwidth links can be hard to
get, particularly in emerging nations. In many places it is difficult
to acquire a 64 kpbs line, and T1 service might not exist.
Furthermore, lead times can be over six months. Even in the US the
cost of transcontinental T1 service is high enough to encourage high
utilization. Cost-conscious businesses want IPng to allow high
utilization of teleprocessing links, but without requiring excessive
processing power to achieve the high utilization. There has been
considerable speculation concerning the goodput through congested
routes when using the Internet's current congestion control
algorithms; instead, it should be measured in a range of realistic
cases. If peak-busy-hour goodput under congestion is near the
theoretical maximum, publicize the data and move on to other
requirements. If not, then the IETF should seek a better standard
(e.g., they might explore XTP's adaptive rate-based approach and
other proposals).
Functions, such as class of service and priority, that let an
enterprise control use of bandwidth also may help meet service level
agreements. On the one hand, it has been said that the absence of
these inhibits TCP/IP usage in corporate networks, especially when
predictable interactive response times are required. On the other
hand, few vendors have felt motivated to implement TCP's architected
type-of-service, and priority tends to be handled in a non-standard
way (e.g., to assure that interactive well-known ports, such as
Telnet, get faster response times than non-interactive well-known
ports, such as file transfer). The IETF should sort out these
apparently conflicting perspectives. If the ad hoc techniques can be
demonstrated to be adequate, then they should be standardized;
otherwise, effective techniques should be developed and standardized.
Commercial users often require the options of a higher level of
service for a higher cost, or a lower level of service for a lower
cost; e.g., some businesses pay top dollar to assure fast response
time during business hours, but choose less expensive satellite
services for data backup during the night. Pervasive use of IPv4's
type-of-service markings might satisfy this requirement.
To discourage waste of bandwidth and other expensive resources,
corporations want to account for their use. Direct cost recovery
would let an entity measure and benchmark its efficiency with minimal
economic distortion. Alternatives, such as placing these costs into
corporate overhead or charging per connection, make sense when the
administrative cost of implementing usage-based accounting is high
enough to introduce more economic distortion than the alternatives
would. For example, connection-based costs alone may be adequate for
a resource (such as LAN bandwidth) that is not scarce or expensive,
but a combination of a connection cost and a usage cost may be more
appropriate for a more scarce or expensive resource (such as WAN
bandwidth). Balance must be maintained between the overhead of
accounting and the granularity of cost allocation.
Security
Many corporations will stick with their private networks until public
ones can guarantee equivalent confidentiality, integrity, and
availability. It is not clear that additional architecture is needed
to satisfy this requirement; perhaps more wide spread use of
existing security technology would suffice. For example, the
Internet could encourage wide deployment of Generic Security Service,
and then solicit feedback on whether additional security requirements
need to be satisfied. Note that businesses are so concerned about
network cost control mechanisms that they want them secured against
tampering. IPng should not interfere with firewalls, which many
corporations consider essential.
Heterogeneity
Corporate users want the Internet to accommodate multiple protocol
suites. Several different protocol suites are growing in use, and
some older ones will be used for many more years. Although many
people wish there were only one protocol in the world, there is
little agreement on which one it should be.
Since the marketplace has not settled on one approach to handling
multiple protocols, IPng should be flexible enough to accommodate a
variety of technical approaches to achieving heterogeneity. For
example, most networking protocols assume they will be the dominate
protocol that transports all others; protocol designers should pay
more attention to making their protocols easily transported by
others. IPng needs to be flexible enough to accommodate the major
multiprotocol trends, including multiprotocol transport networking
(for an example, see X/OPEN document G306), tunneling (both IP being
the tunnel and being tunneled), and link sharing (e.g., point-to-
point protocol and frame relay). Fair sharing of bandwidth by
protocols with different congestion control mechanisms is a
particularly interesting subject.
Flow and Resource Reservation
Corporate users are becoming more interested in transmitting both
non-isochronous and isochronous information together across the same
link. IPng should coexist effectively with the isochronous protocols
being developed for the Internet.
The Internet protocols should take advantage of services that may be
offered by an underlying fast packet switching service. Constant-
bit-rate and variable-bit-rate services typically require
specification of, and conformance to, traffic descriptors and
specification of quality-of-service objectives from applications or
users. The Internet's isochronous protocols should provide
mechanisms to take advantage of multimedia services that will be
offered by fast packet switching networks, and must ensure that
quality-of-service guarantees are preserved all the way up the
protocol stacks to the applications. Protocols using available-bit-
rate services may achieve better bandwidth utilization if they react
to congestion messages from a fast packet switching network, and if
they consider consequences of cell discard (e.g., if one cell of an
IP datagram is discarded, it would be a waste to continue forwarding
the rest of the cells in that datagram; also, selective retransmit
should be revisited in this context).
When the Internet protocol suite allows mixing of non-isochronous and
isochronous traffic on one medium, it should provide mechanisms to
discourage inappropriate reservation of resources; e.g., a Telnet
connection probably doesn't need to reserve 45Mbps. Accounting,
class-of-service, and well-known-port distinctions are possible ways
to satisfy that requirement.
Mobile Hosts
Wireless technology opens up opportunities for new TCP/IP
applications that are specific to mobile hosts. In addition to
coordinating with organizations developing wireless standards, the
IETF also should encourage the specification of new TCP/IP
applications enabled by wireless, such as connectionless messaging.
IPng should deal well with the characteristics (delay, error rates4,
etc.) peculiar to wireless.
Topological flexibility
Today a TCP/IP host moved to a different subnet needs a new IP
address. Such moves and changes can become a significant
administrative cost. Moreover, mobile hosts require flexible
topology. Note how the wireless world is trying to defeat the subnet
model of addressing either by proxy or by IPaddress servers. Perhaps
IPng needs an addressing model more flexible than subnetting, both to
reduce the administrative burden and to facilitate roaming users.
The need to eliminate single points of failure drives the business
requirement for multi-tail attachment of hosts to networks.
Corporate users complain that TCP/IP can non-disruptively switch a
connection from a broken route to a working one only if the new route
leads to the same adapter on the end system.
Configuration, Administration and Operation
Businesses would like dynamic but secure updating of Domain Name
Servers, both to ease moves and changes and to facilitate cutover to
backup hosts. In this vein, secure and dynamic interaction between
DNS and Dynamic Host Configuration Protocol (DHCP, RFC1541) is
required. The IETF should encourage wide deployment of DHCP, and
then solicit feedback on whether additional configuration
requirements need to be satisfied.
Policy-Based Routing
Policy-based routing is a more a solution than a requirement.
Businesses rarely require a general purpose policy architecture,
although they do state requirements that policy-based routing could
satisfy. For example, corporations do not want to carry for free the
transit traffic of other enterprises, and they may not want their
sensitive data to flow through links controlled by certain other
enterprises. Policy-based routing is one possible way to satisfy
those requirements, but there seems to be a concern that general
purpose policy-based routing may have high administrative cost and
low routing performance.
Scaling
If IPng satisfies the scaling requirement of the Internet, then it
satisfies it for corporate networks a fortiori.
Conclusions
Enhancements to the Internet protocol suite, together with wider
deployment of some of its existing architectures, could satisfy these
requirement of commercial customers while retaining IPv4. Expansion
of the address space eventually will be necessary to allow continued
Internet growth, but in RFC1518 Tony Li and Yakov Rehkter have shown
that from a technical perspective the addressing issue of IPng is not
an immediate concern.
Nevertheless, the TCP/IP community should establish a direction for
enlargement of the address space, because unfounded publicity about
the address space is scaring away potential TCP/IP users. If the
IETF does not provide direction on how its address space will grow,
then people may use non-standard, and probably incompatible,
approaches.
Security Considerations
The IETF should encourage wide deployment of GSS API, and then
solicit feedback on whether additional security requirements need to
be satisfied. Businesses are so concerned about network cost control
mechanisms that they want them secured against tampering. IPng
should not interfer with firewalls, which many corporations consider
essential. See other comments on Security throughout this memo.
Authors' Addresses
Edward Britton
IBM Corp.
E69/503
P.O.Box 12195
Research Triangle Park, NC 27709
Phone: (919) 254-6037
EMail:
brittone@vnet.ibm.com
John Tavs
IBM Corp.
E69/503
P.O.Box 12195
Research Triangle Park, NC 27709
Phone: (919) 245-7610
