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draft-ietf-multi6-multihoming-requirements-02-candidate1
- To: multi6@ops.ietf.org
- Subject: draft-ietf-multi6-multihoming-requirements-02-candidate1
- From: Joe Abley <jabley@nlri.org>
- Date: Mon, 12 Nov 2001 05:08:12 -0500
- User-Agent: Mutt/1.3.22.1i
I have completed a rough set of initial edits to the requirements
draft, along the lines discussed here over the last few months.
I haven't submitted this to the rfc editor yet, since I expect more
changes to come out of discussion on the list this week (and I
suspect the rfc editor could do without the additional work right
now). If this is bad form, please let me know.
The text is here:
http://buffoon.automagic.org/dist/draft-ietf-multi6-multihoming-requirements-02-candidate1.txt
and is attached below, depaginated with change bars in the left-
hand margin indicating changed lines, in case someone finds that
useful. The diff was against the -01 draft.
The main changes are:
1. The use of "enterprise" was contentious and I think the consensus
was it was not the best word. I have subsituted "site", and mentioned
the RFC1918 definition of "enterprise" as compatible in the glossary.
2. I have tried to use "site-multihoming" or "multihomed site" to
be more explicit about the kind of multihoming we are talking about.
3. Clarification of the definition of "transit provider", since
it was evident that this term is understood differently by many
different people. I have chosen to clarify the definition I used
previously rather than change it. If the definition below is not
sufficiently familiar to enough people, an alternative would be
welcomed.
4. SHOULD/MUST/etc. Please review.
I have almost certainly missed some other modifications that
someone was expecting, so if they could be pointed out that would
be good.
We have a week, I think, to knock this into shape before the
submission deadline.
Joe
Network Working Group B. Black
Internet-Draft Layer8 Networks
|Expires: May 13, 2002 V. Gill
J. Abley
| MFN
| November 12, 2001
| Requirements for IPv6 Site-Multihoming Architectures
| draft-ietf-multi6-multihoming-requirements-02-candidate1
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
| This Internet-Draft will expire on May 13, 2002.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
| Site-multihoming, i.e. connecting to more than one IP service
| provider, is an essential component of service for many sites which
| are part of the Internet. Existing IPv4 site-multihoming practices,
| described in a companion draft [1], provides a set of capabilities
| that must be accommodated by the adopted site-multihoming
architecture in IPv6, and a set of limitations that must be overcome,
relating in particular to scalability.
| This document outlines a set of requirements for a new IPv6 site-
| multihoming architecture.
1. Introduction
| Current IPv4 site-multihoming practices have been added on to the
| CIDR architecture [2], which assumes that routing table entries can
| be aggregated based upon a hierarchy of customers and service
| providers [1].
However, it appears that this hierarchy is being supplanted by a
dense mesh of interconnections [9]. Additionally, there has been an
| enormous growth in the number of multihomed sites. For purposes of
| redundancy and load-sharing, the multihomed address blocks, which are
| almost always a longer prefix than the provider aggregate, are
| announced along with the larger, covering aggregate originated by the
| provider. This contributes to the rapidly-increasing size of the
| global routing table. This explosion places significant stress on
| the inter-provider routing system.
| Continued growth of both the internet and the practice of site-
| multihoming will seriously exacerbate this stress. The site-
| multihoming architecture for IPv6 should allow the routing system to
| scale more pleasantly.
2. Terminology
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 [4].
| A "site" is an entity autonomously operating a network using IP and,
| in particular, determining the addressing plan and routing policy for
| that network. This definition is intended to be equivalent to
| "enterprise" as defined in [3].
| A "transit provider" operates a site which directly provides
| connectivity to the Internet to one or more external sites. The
| connectivity provided extends beyond the transit provider's own site.
| A transit provider's site is directly connected to the sites for
| which it provides transit.
| A "multihomed" site is one with more than one transit provider.
| "Site-multihoming" is the practice of arranging a site to be multi-
| homed.
| The term "re-homing" denotes a transition of a site between two
| states of connectedness, due to a change in the connectivity between
| the site and its transit providers' sites.
3. Multihoming Requirements
3.1 Capabilities of IPv4 Multihoming
| The following capabilities of current IPv4 multihoming practices MUST
| be supported by an IPv6 multihoming architecture. IPv4 multihoming
| is discussed in more detail in [1].
3.1.1 Redundancy
| By multihoming, a site MUST be able to insulate itself from certain
| failure modes within one or more transit providers, as well as
| failures in the network providing interconnection among one or more
transit providers.
| Infrastructural commonalities below the IP layer may result in
| connectivity which is apparently diverse sharing single points of
| failure. For example, two separate DS3 circuits ordered from
| different suppliers and connecting a site to independent transit
| providers may share a single conduit from the street into a building;
| in this case backhoe-fade of both circuits may be experienced due to
| a single incident in the street. The two circuits are said to "share
| fate".
| The multihoming architecture MUST accommodate (in the general case,
| issues of shared fate notwithstanding) continuity of connectivity
| during the following failures:
| o Physical failure, such as a fiber cut, or router failure,
o Logical link failure, such as a misbehaving router interface,
o Routing protocol failure, such as a BGP peer reset,
o Transit provider failure, such as a backbone-wide IGP failure, and
o Exchange failure, such as a BGP reset on an inter-provider
peering.
3.1.2 Load Sharing
| By multihoming, a site MUST be able to distribute both inbound and
| outbound traffic between multiple transit providers. This
| requirement is for concurrent use of the multiple transit providers,
| not just the usage of one provider over one interval of time and
| another provider over a different interval.
|3.1.3 Performance
| By multihoming, a site MUST be able to protect itself from
| performance difficulties directly between the site's transit
| providers.
| For example, suppose site E obtains transit from transit providers T1
| and T2, and there is long-term congestion between T1 and T2. The
| multihoming architecture MUST allow E to ensure that in normal
| operation none of its traffic is carried over the congested
| interconnection T1-T2. The process by which this is achieved MAY be
| a manual one.
| A multi-homed site MUST be able to distribute inbound traffic from
| particular multiple transit providers according to the particular
| address range within their site which is sourcing or sinking the
| traffic.
3.1.4 Policy
A customer may choose to multihome for a variety of policy reasons
| beyond technical scope (e.g. cost, acceptable use conditions, etc.)
For example, customer C homed to ISP A may wish to shift traffic of a
certain class or application, NNTP, for example, to ISP B as matter
| of policy. A new IPv6 multihoming proposal MUST provide support for
| site-multihoming for external policy reasons.
3.1.5 Simplicity
As any proposed multihoming solution must be deployed in real
networks with real customers, simplicity is paramount. The current
multihoming solution is quite straightforward to deploy and maintain.
| A new IPv6 multihoming proposal MUST NOT be substantially more
complex to deploy and operate than current IPv4 multihoming
practices.
3.1.6 Transport-Layer Survivability
| Multihoming solutions MUST provide re-homing transparency for
| transport-layer sessions; i.e. exchange of data between devices on
| the multihomed site and devices elsewhere on the Internet may proceed
| with no greater interruption than that associated with the transient
| packet loss during the re-homing event.
| New transport-layer sessions MUST be able to be created following a
| re-homing event.
| Transport-layer sessions include those involving transport-layer
| protocols such as TCP, UDP and SCTP over IP. Applications which
| communicate over raw IP and other network-layer protocols MAY also
| enjoy re-homing transparency.
3.2 Additional Requirements
3.2.1 Scalability
Current IPV4 multihoming practices contribute to the significant
growth currently observed in the state held in the global inter-
provider routing system; this is a concern both because of the
hardware requirements it imposes and also because of the impact on
the stability of the routing system. This issue is discussed in
great detail in [9].
| A new IPv6 multihoming architecture MUST scale to accommodate orders
| of magnitude more multi-homed sites without imposing unreasonable
| requirements on the routing system.
3.2.2 Impact on Routers
| The solution MAY require changes to IPv6 router implementations, but
these changes must be either minor, or in the form of logically
separate functions added to existing functions.
| Such changes MUST NOT prevent normal single-homed operation, and
routers implementing these changes must be able to interoperate fully
with hosts and routers not implementing them.
3.2.3 Impact on Hosts
| The solution MUST NOT destroy IPv6 connectivity for a legacy host
implementing RFC 2373 [5], RFC 2460 [7], RFC 2553 [8] and other basic
| IPv6 specifications current in November 2001. That is to say, if a
| host can work in a single-homed site, it must still be able to work
| in a multihomed site, even if it cannot benefit from site-
| multihoming.
It would be compatible with this requirement for such a host to lose
| connectivity if a site lost connectivity to one transit provider,
| despite the fact that other transit provider connections were still
| operational.
If the solution requires changes to the host stack, these changes
| MUST be either minor, or in the form of logically separate functions
added to existing functions.
If the solution requires changes to the socket API and/or the
| transport layer, it MUST be possible to retain the original socket
API and transport protocols in parallel, even if they cannot benefit
from multihoming.
| The multi-homing solution MAY allow host or application changes if
| that would enhance session survivability.
3.2.4 Interaction between Hosts and the Routing System
| The solution MAY involve interaction between a site's hosts and its
| routing system; such an interaction MUST be simple, scaleable and
securable.
3.2.5 Operations and Management
| It MUST be posssible for staff responsible for the operation of a
| site to monitor and configure the site's multihoming system.
4. Security Considerations
| A multihomed site MUST be no more vulnerable to security breaches
| than a non-multihomed site.
References
[1] Abley, J., Black, B. and V. Gill, "IPv4 Multihoming Motivation,
Practices and Limitations (work-in-progress)", I-D draft-ietf-
multi6-v4-multihoming-00, June 2001,
<http://www.automagic.org/~jabley/draft-ietf-multi6-v4-
multihoming-00.txt>.
[2] Fuller, V., Li, T., Yu, J. and K. Varadhan, "Classless Inter-
Domain Routing (CIDR): an Address Assignment and Aggregation
Strategy", RFC 1519, September 1993.
[3] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G. and E.
Lear, "Address Allocation for Private Internets", RFC 1918,
February 1996.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[5] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[6] Hinden, R., O'Dell, M. and S. Deering, "An IPv6 Aggregatable
Global Unicast Address Format", RFC 2374, July 1998.
[7] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[8] Gilligan, R., Thomson, S., Bound, J. and W. Stevens, "Basic
Socket Interface Extensions for IPv6", RFC 2553, March 1999.
[9] Huston, G., "Analyzing the Internet's BGP Routing Table",
January 2001.
Authors' Addresses
Benjamin Black
Layer8 Networks
EMail: ben@layer8.net
Vijay Gill
| MFN
8075 Leesburg Pike
Suite 300
Vienna, VA 22182
US
Phone: +1 410 262 0660
| EMail: vgill@mfn.com
Joe Abley
| MFN
| 10805 Old River Road
| Komoka, ON N0L 1R0
Canada
| Phone: +1 519 641 3738
| EMail: jabley@mfn.com
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