Subject: RE: [RADIR] draft note solicting review

From: "Azinger, Marla" <[email-masked]>
Date: Wed, 23 May 2007 11:24:57 -0400

I think the cover letter/intro are sufficient.  Thank you Thomas.

Marla

-----Original Message-----
From: Thomas Narten [mailto:[email-masked]]
Sent: Tuesday, May 22, 2007 7:55 PM
To: [email-masked]
Subject: [RADIR] draft note solicting review

Per today's call, the plan is to slowly expand the scope of review of
the problem statement. The next step is to run it by the INT/RTG/OPS
ADs and the RRG chairs. The next step after that is to post it to the
RAM list and let the IAB/IESG at it as well. Given the IAB's retreat
starting May 31, our goal is to have the problem statement ready to
send to the RAM list on Wednesday the 30th.

Things we need to do for next Wednesday:

  Add section/paragraph to problem statement saying what we do NOT
  consider to be part of the problem  (mobility in particular) (I'll
  volunteer to take a stab at this.)

  Fill in the pressures on routing section.  Preface with a note
  saying the intention is to catalog all the pressures and that we
  specifially invite comments/additions here. The pressures section
  doesn't have to be perfect, but we need to have a first-cut.

  Volunteers for any of the subsections in 4 & 5 (document below)

Here is a draft note for the next level of review. Per the call, any
comments on the note would be appreciated. Unless I hear otherwise,
I'll send it out at around 1PM EDT on Wednesday.

INT/RTG/OPS ADs, RRG Chairs:

The Routing & Addressing Directorate has produced a first-cut at a
problem statement. At this point, the statement has been reviewed by
the directorate and by Russ Housley and Olaf Kolkman. We are now ready
to expand the circle of reviewers and seek your input/feedback. Our
current plan is to get feedback from you, revise the statement as
appropriate and then send it for wider review on the RAM list.  We
hope to be able to do that by Wednesday, May 30, so that the IAB can
also review the statement at its retreat next week. Hence, it would be
helpful if you could review and respond quickly.

Our main focus has been on Section 3. It is that section in particular
we request review of.

Sections 4 & 5 are just placeholders, and we hope to fill those in
over the next week. But we do not view that section as the critical
ones. We also expect that that section will be expanded as the
document receives wider review.

Here is the document:

Network Working Group                                          T. Narten
Internet-Draft                                              May 15, 2007
Intended status: Informational
Expires: November 16, 2007

                Routing and Addressing Problem Statement
               draft-narten-ram-problem-statement-00.txt

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Abstract

   Problem statement for the route scaling problem.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terms and Definitions  . . . . . . . . . . . . . . . . . . . .  4
   3.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Technical Challenge  . . . . . . . . . . . . . . . . . . .  5
     3.2.  Business Challenge . . . . . . . . . . . . . . . . . . . .  6
     3.3.  Alignment of Incentives  . . . . . . . . . . . . . . . . .  6
     3.4.  Table Growth Targets . . . . . . . . . . . . . . . . . . .  7
   4.  Pressures To Deaggregate . . . . . . . . . . . . . . . . . . .  8
     4.1.  Traffic Engineering  . . . . . . . . . . . . . . . . . . .  8
     4.2.  Multihoming  . . . . . . . . . . . . . . . . . . . . . . .  8
     4.3.  End Site Renumbering . . . . . . . . . . . . . . . . . . .  8
     4.4.  Acquisitions and Mergers . . . . . . . . . . . . . . . . .  8
     4.5.  RIR IPv4 Policies favor Conservation over Aggregation  . .  8
   5.  Pressures on Routing Update Rate . . . . . . . . . . . . . . .  9
     5.1.  Interconnection Richness . . . . . . . . . . . . . . . . .  9
     5.2.  Multihoming  . . . . . . . . . . . . . . . . . . . . . . .  9
     5.3.  Traffic Engineering  . . . . . . . . . . . . . . . . . . .  9
     5.4.  Questionable Operational Practices?  . . . . . . . . . . .  9
     5.5.  RIR IPv6 Policy is Not Balanced  . . . . . . . . . . . . .  9
   6.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 12
   9.  Informative References . . . . . . . . . . . . . . . . . . . . 13
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 15

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1.  Introduction

   Prompted in part by the recent IAB workshop on Routing & Addressing
   [RAWS-REPORT], there has been a renewed focus on the problem of
   routing scalability within the Internet.  The issue itself is not
   new, with discussions dating back at least 10-15 years [GSE, ...].

   This document attempts to define the "problem", with the aim of
   describing the essential aspects so that the community has a way of
   evaluating whether proposed solutions actually address or impact the
   underlying problem or "pain points" in a significant manner.

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2.  Terms and Definitions

   Default Free Zone (DFZ):  That part of the Internet where routers
      maintain full routing tables.  Many routers maintain only partial
      routes, having explicit routes for "local" destinations plus a
      "default" for everything else.  For such routers, building and
      maintaining routing tables is relatively simple because the amount
      of information learned and maintained can be small.  In contrast,
      routers in the DFZ maintain complete information about all
      reachable destinations, which number in the hundreds of the
      thousands of entries.

   Routing Information Base (RIB):  The data structures a router
      maintains that hold the information about destinations (i.e.,
      prefixes) and paths to those destinations.  The amount of state
      information maintained is dependent on a number of factors,
      including the number of individual prefixes, the number of BGP
      peers, the number of distinct paths, etc.  The RIB may also
      include information about unused ("backup") paths for a given
      prefix as well as the active path(s) used for forwarding.

   Forwarding Information Base (FIB):  The actual table used while
      making forwarding decisions for individual packets.  The FIB is a
      compact, optimized version of the RIB, containing only the
      information needed to actually forward individual packets, i.e.,
      mapping a packet's destination address to an outgoing interface
      and next-hop.  The FIB only stores information about paths
      actually used for forwarding; it typically does not store
      information about backup paths.

   Trafic Engineering (TE):  In this document, "traffic engineering"
      refers to the current practice of inbound, inter-AS traffic
      engineering.  This is accomplished by placing more specific routes
      in the routing table and/ or increasing the frequency of routing
      updates in order to control inbound traffic at the boundary of an
      Autonomous system (AS).

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3.  Background

   Within the DFZ, both the size of the RIB and FIB and the overall
   update rate have historically increased at a greater than linear
   rate.  Specifically:

   o  The number of individual prefixes that are propagated into the DFZ
      is increasing at a super-linear rate.  The reasons behind this
      increase are varied and discussed below.  Because each individual
      prefix requires resources to process, any increase in the number
      of prefixes requires a corresponding increase in resources.  Each
      individual prefix that appears in routing updates requires state
      in the RIB (and possibly the FIB) and consumes processing
      resources when updates related to the prefix are received.

   o  The overall rate of routing updates is increasing, requiring
      routers to process updates at an increased rate or converge more
      slowly if they cannot.  The rate increase is driven by a number of
      factors (discussed below).  It should be noted that the overall
      routing update rate is dependent on two factors: the number of
      individual prefixes and the mean per-prefix update rate.  While it
      is clear that the overall number of prefixes is increasing super-
      linearly, further study is needed to determine whether the mean
      per-prefix update rate is increasing as well [need reference].

   This super linear growth presents a scalability challenge for current
   and/or future routers.  There are two aspects to the challenge.  The
   first one is purely technical: can we build routers (i.e., hardware &
   software) actually capable handling the load, both today and going
   forward?  The second challenge is one of economics: is the cost of
   developing, building and deploying such routers economically
   sustainable, given current and realistic business models that govern
   how ISPs operate as businesses?

3.1.  Technical Challenge

   The technical challenge of building routers relates to the resources
   needed to process a larger and increasingly dynamic amount of routing
   information.  More specifically, routers must maintain an increasing
   amount of associated state information in the RIB, they must be
   capable of populating a growing FIB, they must perform forwarding
   lookups at line rates (while accessing the FIB) and they must be able
   to initialize the RIB and FIB at boot time.  Moreover, this activity
   must take place within acceptable time frames (i.e., the overall
   system must converge and stabilize within an acceptable time period).
   Finally, the hardware needed to achieve this cannot have unreasonable
   power consumption or cooling demands.

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3.2.  Business Challenge

   Even if it is technically possible to build routers capable of
   meeting the technical and operational requirements, it is also
   necessary that the overall cost to build, maintain and deploy such
   equipment meet reasonable business expectations.  ISPs, after all,
   are run as businesses.  As such, they must be able to plan, develop
   and construct viable business plans that provide an acceptable return
   on investment (i.e., one acceptable to investors).

   One aspect of planning concerns the assumptions made about the
   expected usable lifetime of purchased equipment.  Businesses
   typically expect that once deployed, equipment can remain in use for
   some projected amount of time (e.g., 3-5 years).  Upgrading equipment
   earlier than planned is more easily justified (as an unplanned
   expense) when a new business opportunity is enabled as a result of an
   upgrade.  For example, an upgrade might be justified by an ability to
   support increased traffic or an increase in the number of customer
   connections, etc., where the upgrade can translate into increased
   revenue.  In contrast, it is more difficult to justify unplanned
   upgrades in the absence of corresponding customer benefit (and
   revenue) to cover the upgrade cost.  It is generally desired that
   deployed equipment remain usable over its planned lifetime.  An
   increase in the resources required to support larger or more dynamic
   routing tables is viewed as a sort of "unfunded mandate", in that
   customers do not expect to have to pay more just to continue
   retaining the same level of service as before, i.e., having all
   destinations be reachable as was the case in the past.  This
   undermining of planning is particularly problematic when the increase
   in routing demand originates external to the ISP, and the ISP has no
   way to control or limit it (e.g., the increased demand comes from
   being part of the DFZ).

   From a business perspective, it is desirable to maintain or increase
   the useful lifespan of routing equipment, by improving the scaling
   properties of the routing and addressing system.

3.3.  Alignment of Incentives

   Today's growth pattern is influenced by the scaling properties of the
   current system.  If the system had better scaling properties, we
   would be able support and enable more widespread usage of certain
   applications such as multihoming and traffic engineering.  Currently
   the system does not allow everyone to multihome, as there are some
   barriers to multihoming due to operational practices that try to
   strike a balance between the amount of multihoming and preservation
   of routing slots.  It is desirable that the routing and addressing
   system exert the least possible back pressure on end user

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   applications and deployment scenarios, to enable the broadest
   possible use of the Internet.

   One aspect of the current architecture is a misalignment of cost and
   benefit.  Injecting individual prefixes into the DFZ creates a small
   amount of "pain" for those routers that are part of the DFZ.  Each
   individual prefix has a small cost, but the aggregate sum of all
   prefixes is significant, and leads to the core problem at hand.
   Those that inject prefixes into the DFZ do not generally pay the cost
   associated with the individual prefix -- it is carried by the routers
   in the DFZ.  But the originator of the prefix receives the benefit.
   Hence, there is misalignment of incentives between those receiving
   the benefit and those bearing the cost of providing the benefit.
   Consequently, incentives are not aligned properly to produce a
   natural balance between the cost and benefit of maintaining routing
   tables.

3.4.  Table Growth Targets

   A precise target for the rate of table size or routing update
   increase that should reasonably be supported going forward is
   difficult to state in quantitative terms.  One target might simply be
   to keep the growth at a stable, but manageable growth rate so that
   the increased router functionality can roughly be covered by
   improvements in technology (e.g., increased processor speeds,
   reductions in component costs, etc.).

   However, it is highly desirable to significantly bring down (or even
   reverse) the growth rate in order to meet user expectations for
   specific services.  As discussed below, there are numerous pressures
   to deaggregate routes.  These pressures come from users seeking
   specific, tangible service improvements that provide "business-
   critical" value.  Today, some of those services simply cannot be
   supported to the degree that future demand can be reasonably be
   expected because of the negative implications on DFZ table growth.
   Hence, valuable services are available to some, but not all potential
   customers.  As the need for such services becomes increasingly
   important, it will be difficult to deny such services to large
   numbers of users, especially when some "lucky" sites are able to use
   the service and others are not.

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4.  Pressures To Deaggregate

   Note: the remainder of this document is in rough outline form and
   remains to be completed.  We decided to defer completing this section
   in order to focus on the problem statement in Section 3 first.

   There are a number of factors behind the increase in the quantity of
   prefixes appearing in the DFZ.  From a theoretical perspective, the
   number of prefixes in the DFZ can be minimized through aggressive
   aggregation [RFC4632].  In practice, strict adherence to the CIDR
   principles is difficult.

4.1.  Traffic Engineering

   Simply include Section 3.1.3 of RAWS Report?

4.2.  Multihoming

   Simply include Section 3.1.2 of RAWS Report?

4.3.  End Site Renumbering

   Pain of end site renumbering leads to demand for PI assignments, each
   of which translates into an additional prefix in the DFZ.

4.4.  Acquisitions and Mergers

4.5.  RIR IPv4 Policies favor Conservation over Aggregation

   Especially in IPv4, subsequent allocations not always from same block
   as previous allocation...

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5.  Pressures on Routing Update Rate

5.1.  Interconnection Richness

5.2.  Multihoming

5.3.  Traffic Engineering

5.4.  Questionable Operational Practices?

5.5.  RIR IPv6 Policy is Not Balanced

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6.  Problem Statement

   There is a need for an approach to routing and addressing that:

   1.  reduces the growth rate of the size of the DFZ routing load

   2.  allows any end site wishing to multihome to do so

   3.  Supports ISP and enterprise TE needs

   4.  Allows end sites to switch providers while minimizing
       configuration changes to internal end site devices.

   5.  Provides meaningful benefits to the parties who bear the costs of
       deploying and maintaining the technology.

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7.  Security Considerations

   None.

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8.  Acknowledgments

   The initial version of this document was produced by the Routing and
   Addressing Directorate (http://www.ietf.org/IESG/content/radir.html).
   The membership of the directorate at that time included Marla
   Azinger, Vince Fuller, Vijay Gill, Thomas Narten, Erik Nordmark,
   Jason Schiller, Peter Schoenmaker, and John Scudder.

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9.  Informative References

   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
              (CIDR): The Internet Address Assignment and Aggregation
              Plan", BCP 122, RFC 4632, August 2006.

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Author's Address

   Thomas Narten (Editor)

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Full Copyright Statement

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