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Keywords: routing architecture, addressing architecture
Internet Research Task Force (IRTF) T. Li, Ed.
Request for Comments: 6227 Cisco Systems, Inc.
Category: Informational May 2011
ISSN: 2070-1721
Design Goals for Scalable Internet Routing
Abstract
It is commonly recognized that the Internet routing and addressing
architecture is facing challenges in scalability, mobility, multi-
homing, and inter-domain traffic engineering. The Routing Research
Group is investigating an alternate architecture to meet these
challenges. This document consists of a prioritized list of design
goals for the target architecture.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Research Task Force
(IRTF). The IRTF publishes the results of Internet-related research
and development activities. These results might not be suitable for
deployment. This RFC represents the consensus of the Routing
Research Group of the Internet Research Task Force (IRTF). Documents
approved for publication by the IRSG are not a candidate for any
level of Internet Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6227.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
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RFC 6227 Scalable Routing Design Goals May 2011
Table of Contents
1. Introduction ....................................................2
1.1. Requirements Language ......................................3
1.2. Priorities .................................................3
2. General Design Goals Collected from the Past ....................3
3. Design Goals for a New Routing Architecture .....................3
3.1. Improved Routing Scalability ...............................3
3.2. Scalable Support for Traffic Engineering ...................4
3.3. Scalable Support for Multi-Homing ..........................4
3.4. Decoupling Location and Identification .....................4
3.5. Scalable Support for Mobility ..............................5
3.6. Simplified Renumbering .....................................5
3.7. Modularity, Composability, and Seamlessness ................6
3.8. Routing Quality ............................................6
3.9. Routing Security ...........................................7
3.10. Deployability .............................................7
3.11. Summary of Priorities .....................................7
4. Security Considerations .........................................7
5. References ......................................................8
5.1. Normative References .......................................8
5.2. Informative References .....................................8
1. Introduction
It is commonly recognized that the Internet routing and addressing
architecture is facing challenges in inter-domain scalability,
mobility, multi-homing, and inter-domain traffic engineering
[RFC4984]. The Routing Research Group (RRG) aims to design an
alternate architecture to meet these challenges. This document
presents a prioritized list of design goals for the target
architecture.
These goals should be taken as guidelines for the design and
evaluation of possible architectural solutions. The expectation is
that these goals will be applied with good judgment.
The goals presented here were initially presented and discussed at
the start of the RRG work on a revised routing architecture, and were
revisited and finalized after the work on that architecture was
complete. As such, this represents both the goals that the RRG
started with, and revisions to those goals based on our increased
understanding of the space.
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RFC 6227 Scalable Routing Design Goals May 2011
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
1.2. Priorities
Each design goal in this document has been assigned a priority, which
is one of the following: 'required', 'strongly desired', or
'desired'.
Required:
The solution is REQUIRED to support this goal.
Strongly desired:
The solution SHOULD support this goal, unless there exist
compelling reasons showing that it is unachievable, extremely
inefficient, or impractical.
Desired:
The solution SHOULD support this goal.
2. General Design Goals Collected from the Past
[RFC1958] provides a list of the original architectural principles of
the Internet. We incorporate them here by reference, as part of our
desired design goals.
3. Design Goals for a New Routing Architecture
3.1. Improved Routing Scalability
Long experience with inter-domain routing has shown that the global
BGP routing table is continuing to grow rapidly [BGPGrowth].
Carrying this large amount of state in the inter-domain routing
protocols is expensive and places undue cost burdens on network
participants that do not necessarily get value from the increases in
the routing table size. Thus, the first required goal is to provide
significant improvement to the scalability of the inter-domain
routing subsystem. It is strongly desired to make the routing
subsystem scale independently from the growth of the Internet user
population. If there is a coupling between the size of the user base
and the scale of the routing subsystem, then it will be very
difficult to retain any semblance of scalability. If a solution
includes support for alternative routes to support faster
convergence, the alternative routes should also factor into routing
subsystem scalability.
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RFC 6227 Scalable Routing Design Goals May 2011
3.2. Scalable Support for Traffic Engineering
Traffic engineering is the capability of directing traffic along
paths other than those that would be computed by normal IGP/EGP
routing. Inter-domain traffic engineering today is frequently
accomplished by injecting more-specific prefixes into the global
routing table, which results in a negative impact on routing
scalability. The additional prefixes injected to enable traffic
engineering place an added burden on the scalability of the routing
architecture. At the same time, the need for traffic engineering
capabilities is essential to network operations. Thus, a scalable
solution for inter-domain traffic engineering is strongly desired.
3.3. Scalable Support for Multi-Homing
Multi-homing is the capability of an organization to be connected to
the Internet via more than one other organization. The current
mechanism for supporting multi-homing is to let the organization
advertise one prefix or multiple prefixes into the global routing
system, again resulting in a negative impact on routing scalability.
More scalable solutions for multi-homing are strongly desired.
3.4. Decoupling Location and Identification
Numerous sources have noted that an IP address embodies both host
attachment point information and identification information [IEN1].
This overloading has caused numerous semantic collisions that have
limited the flexibility of the Internet architecture. Therefore, it
is desired that a solution separate the host location information
namespace from the identification namespace.
Caution must be taken here to clearly distinguish the decoupling of
host location and identification information, and the decoupling of
end-site addresses from globally routable prefixes; the latter has
been proposed as one of the approaches to a scalable routing
architecture. Solutions to both problems, i.e., (1) the decoupling
of host location and identification information and (2) a scalable
global routing system (whose solution may, or may not, depend on the
second decoupling) are required, and it is required that their
solutions are compatible with each other.
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3.5. Scalable Support for Mobility
Mobility is the capability of a host, network, or organization to
change its topological connectivity with respect to the remainder of
the Internet, while continuing to receive packets from the Internet.
Existing mechanisms to provide mobility support include
1. renumbering the mobile entity as it changes its topological
attachment point(s) to the Internet;
2. renumbering and creating a tunnel from the entity's new
topological location back to its original location; and
3. letting the mobile entity announce its prefixes from its new
attachment point(s).
The first approach alone is considered unsatisfactory, as the change
of IP address may break existing transport or higher-level
connections for those protocols using IP addresses as identifiers.
The second requires the deployment of a 'home agent' to keep track of
the mobile entity's current location and adds overhead to the routers
involved, as well as adding stretch to the path of an inbound packet.
Neither of the first two approaches impacts the routing scalability.
The third approach, however, injects dynamic updates into the global
routing system as the mobile entity moves. Mechanisms that help to
provide more efficient and scalable mobility support are desired,
especially when they can be coupled with security -- especially
privacy -- and support topological changes at a high rate. Ideally,
such mechanisms should completely decouple mobility from routing.
3.6. Simplified Renumbering
Today, many of the end-sites receive their IP address assignments
from their Internet Service Providers (ISPs). When such a site
changes providers, for routing to scale, the site must renumber into
a new address block assigned by its new ISP. This can be costly,
error-prone, and painful [RFC5887]. Automated tools, once developed,
are expected to provide significant help in reducing the renumbering
pain. It is not expected that renumbering will be wholly automated,
as some manual reconfiguration is likely to be necessary for changing
the last-mile link. However, the overall cost of renumbering should
be drastically lowered.
In addition to being configured into hosts and routers, where
automated renumbering tools can help, IP addresses are also often
used for other purposes, such as access control lists. They are also
sometimes hard-coded into applications used in environments where
failure of the DNS could be catastrophic (e.g., certain remote
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RFC 6227 Scalable Routing Design Goals May 2011
monitoring applications). Although renumbering may be considered a
mild inconvenience for some sites, and guidelines have been developed
for renumbering a network without a flag day [RFC4192], for others,
the necessary changes are sufficiently difficult so as to make
renumbering effectively impossible. It is strongly desired that a
new architecture allow end-sites to renumber their network with
significantly less disruption, or, if renumbering can be eliminated,
the new architecture must demonstrate how the topology can be
economically morphed to fit the addressing.
3.7. Modularity, Composability, and Seamlessness
A new routing architecture should be modular: it should subdivide
into multiple composable, extensible, and orthogonal subsystems. The
interfaces between modules should be natural and seamless, without
special cases or restrictions. Similarly, the primitives and
abstractions in the architecture should be suitably general, with
operations equally applicable to abstractions and concrete entities,
and without deleterious side-effects that might hinder communication
between endpoints in the Internet. These properties are strongly
desired in a solution.
As an example, if tunneling were used as a part of a solution,
tunneling should be completely transparent to both of the endpoints,
without requiring new mechanisms for determining the correct maximum
datagram size.
The resulting network should always fully approximate the current
best-effort Internet connectivity model, and it should also
anticipate changes to that model, e.g., for multiple differentiated
and/or guaranteed levels of service in the future.
3.8. Routing Quality
The routing subsystem is responsible for computing a path from any
point in the Internet to any other point in the Internet. The
quality of the routes that are computed can be measured by a number
of metrics, such as convergence, stability, and stretch.
The stretch factor is the maximum ratio between the length of a
route computed by the routing scheme and that of a shortest path
connecting the same pair of nodes [JACM89].
A solution is strongly desired to provide routing quality equivalent
to what is available today, or better.
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RFC 6227 Scalable Routing Design Goals May 2011
3.9. Routing Security
Currently, the routing subsystem is secured through a number of
protocol-specific mechanisms of varying strength and applicability.
Any new architecture is required to provide at least the same level
of security as is deployed as of when the new architecture is
deployed.
3.10. Deployability
A viable solution is required to be deployable from a technical
perspective. Furthermore, given the extensive deployed base of
today's Internet, a solution is required to be incrementally
deployable. This implies that a solution must continue to support
those functions in today's routing subsystem that are actually used.
This includes, but is not limited to, the ability to control routing
based on policy.
3.11. Summary of Priorities
The following table summarizes the priorities of the design goals
discussed above.
+------------------------+------------------+
| Design goal | Priority |
+------------------------+------------------+
| Scalability | Strongly desired |
| Traffic engineering | Strongly desired |
| Multi-homing | Strongly desired |
| Loc/id separation | Desired |
| Mobility | Desired |
| Simplified renumbering | Strongly desired |
| Modularity | Strongly desired |
| Routing quality | Strongly desired |
| Routing security | Required |
| Deployability | Required |
+------------------------+------------------+
4. Security Considerations
All solutions are required to provide security that is at least as
strong as the existing Internet routing and addressing architecture.
This document does not suggest any default architecture or protocol,
and thus this document introduces no new security issues.
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RFC 6227 Scalable Routing Design Goals May 2011
5. References
5.1. Normative References
[RFC1958] Carpenter, B., Ed., "Architectural Principles of the
Internet", RFC 1958, June 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day",
RFC 4192, September 2005.
[RFC4984] Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed.,
"Report from the IAB Workshop on Routing and
Addressing", RFC 4984, September 2007.
[RFC5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering
Still Needs Work", RFC 5887, May 2010.
5.2. Informative References
[BGPGrowth] Huston, G., "BGP Routing Table Analysis Reports",
<http://bgp.potaroo.net/>.
[IEN1] Bennett, C., Edge, S., and A. Hinchley, "Issues in the
Interconnection of Datagram Networks", Internet
Experiment Note (IEN) 1, INDRA Note 637, PSPWN 76,
July 1977, <http://www.postel.org/ien/pdf/ien001.pdf>.
[JACM89] Peleg, D. and E. Upfal, "A trade-off between space and
efficiency for routing tables", Journal of the
ACM Volume 36, Issue 3, July 1989,
<http://portal.acm.org/citation.cfm?id=65953>.
Author's Address
Tony Li (editor)
Cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
USA
Phone: +1 408 853 9317
EMail: tli@cisco.com
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