Design Goals for Scalable Internet Routing
draft-irtf-rrg-design-goals-03

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 RRG is designing an alternate architecture to meet these challenges. This document consists of a prioritized list of design goals for the architecture.

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Table of Contents

1.  Introduction
    1.1.  Requirements Language
    1.2.  Priorities
2.  General Design Goals Collected from Past
3.  Design Goals for A New Routing Architecture
    3.1.  Improved routing scalability
    3.2.  Scalable support for traffic engineering
    3.3.  Scalable support for multi-homing
    3.4.  Scalable support for mobility
    3.5.  Simplified renumbering
    3.6.  Decoupling location and identification
    3.7.  First-class elements
    3.8.  Routing quality
    3.9.  Routing security
    3.10.  Deployability
4.  IANA Considerations
5.  Security Considerations
6.  References
    6.1.  Normative References
    6.2.  Informative References
§  Author's Address

1.  Introduction

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 aims to design an alternate architecture to meet these challenges. This document presents a prioritized list of design goals for the architecture.

These goals should be taken as guidelines for evaluating possible architectural solutions. The expectation is that these goals will be applied with good judgment.

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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

1.2.  Priorities

Each design goal in this document has been assigned a priority, which is one of 'required', 'strongly desired', 'desired', and 'optional'.

Required:

The solution is REQUIRED to support this goal.

Strongly desired:

The solution SHOULD support this goal unless there exist compelling reasons showing it is unachievable, extremely inefficient, or impractical.

Desired:

The solution SHOULD support this goal.

Optional:

The solution MAY support this goal.

It is possible that two design goals at the same priority level may be found to be in conflict with one another. If and when this happens, one of them may be subsequently re-prioritized to have the two in different priority levels.

2.  General Design Goals Collected from Past

RFC 1958 (Carpenter, B., “Architectural Principles of the Internet,” June 1996.) [RFC1958] provides an excellent 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 us that the global BGP routing table is continuing to grow rapidly [BGPGrowth] (Huston, G., “BGP Routing Table Analysis Reports,” .). Carrying this large amount of state in the control plane 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 control plane. It is strongly desired to make the control plane scale independently from the growth of the Internet user population. If a solution includes support for alternative routes to support faster convergence, the alternative routes should also factor into control plane scalability.

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. 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 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.  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 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.

3.5.  Simplified renumbering

Today many of the end-sites receive their IP address assignments from their Internet Service Providers (ISP). 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. 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 this transition 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 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] (Baker, F., Lear, E., and R. Droms, “Procedures for Renumbering an IPv6 Network without a Flag Day,” September 2005.), 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.

3.6.  Decoupling location and identification

Numerous sources have noted that an IPv4 address embodies both host attachment point information and identification information. 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.

3.7.  First-class elements

In the branch of computer science that is devoted to programming language design, there is an explicit notion of a "first-class element" in the design. These are language elements that are fully integrated into the language, with clear, consistent, logical and natural semantics and obvious interactions with all of the other elements in the language [FirstClass] (, “First-class object,” .).

For our architectural purposes, it is strongly desired that the primary mechanisms in an architecture all be first-class elements. More specifically, if a tunneling mechanism is used to provide network layering, connectivity virtualization, or a connection-oriented mode, then it is strongly desired that the tunneling mechanism be a first-class element in the architecture. This requires that the issues of path MTU, reachability, and recursion be addressed.

3.8.  Routing quality

The routing subsystem is responsible for computing a path from any point on 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 scheme and that of a shortest path connecting the same pair of nodes. [JACM89] (Peleg, D. and E. Upfal, “A trade-off between space and efficiency for routing tables,” July 1989.)

A solution is strongly desired to provide routing quality equivalent to what is available today or better.

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

Since solutions that are not deployable are simply academic exercises, solutions are 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.

4.  IANA Considerations

This memo includes no requests to IANA.

5.  Security Considerations

All solutions are required to provide security that is at least as strong as the existing Internet routing and addressing architecture.

6.  References

6.1. Normative References

6.2. Informative References

Author's Address