Subject: [RADIR] another cut at problem statement

From: Thomas Narten <[email-masked]>
Date: Mon, 14 May 2007 13:52:00 -0400

Full document below.

Here are the main changes/additions:

New definition:

> 2.  Terms and Definitions
> 
>    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).

...

Redid this, mostly in second paragraph, per discussion on call.

> 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.

New section (also per call discussion):
      
> 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.

Thomas

Network Working Group                                          T. Narten
Internet-Draft                                              May 14, 2007
Intended status: Informational
Expires: November 15, 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
     5.6.  Questionable Operational Practices?  . . . . . . . . . . .  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

5.6.  Questionable Operational Practices?

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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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---

From: "vijay gill" <[email-masked]>
Date: Mon, 14 May 2007 11:51:13 -0700

> Full document below.

Looks good. A few minor reworkings below.

>       updates in order to control inbound traffic at the boundary of an
I would just remove inbound. Just say inter-AS, we can do this without
loss of generality.

>       per-prefix update rate is increasing as well [need reference].

The reference for growth could be Geoff Hustons http://bgp.potaroo.net/ site

>    Simply include Section 3.1.3 of RAWS Report?

Not quite as crisp as the language used here, but it can be used for
now and we can firm it up later.

> 5.1.  Interconnection Richness

This speaks more to number of paths at the edge routers and
processing/RAM needed to take care of doing the initial BGP
computation of selecting best paths that are then propagated out to
the core.

> 5.3.  Traffic Engineering

This is needed here?

> 5.4.  Questionable Operational Practices?
Deaggregation for "security" to prevent people from accidentally or
maliciously announcing more specifics. Eg Covad got hijacked from
russia and then started announcing /24s entirely.

> 5.6.  Questionable Operational Practices?

Dup

>        deploying and maintaining the technology.

This looks good. A checklist each solution can be verified against. #3
means TE, and that is going to be hard to reconcile with #5. Have we
looked at a cost model for route propagation?

/vijay

---

From: Jason Schiller <[email-masked]>
Date: Mon, 14 May 2007 16:48:29 -0400 (EDT)

I agree everything looks good... I just wanted to make one comment about
"inbound".  I'm not necessarily saying we should keep "inbound" but the
reason why it was in there in the first place was to seperate this
practice from outbound TE where additional prefixes are not generally
advertised...  If this distinction is not useful or necessary, then we can
remove it. 

In fact I think the origional text lacked it, but someone was looking for
a more accurate definition of TE.

__Jason

==========================================================================
Jason Schiller                                               (703)886.6648
Senior Internet Network Engineer                         fax:(703)886.0512
Public IP Global Network Engineering                       [email-masked]
UUNET / Verizon                         [email-masked]

The good news about having an email address that is twice as long is that
it increases traffic on the Internet.

On Mon, 14 May 2007, vijay gill wrote:

> Date: Mon, 14 May 2007 11:51:13 -0700
> From: vijay gill <[email-masked]>
> To: Thomas Narten <[email-masked]>
> Cc: [email-masked]
> Subject: Re: [RADIR] another cut at problem statement
>

---

From: "John G. Scudder" <[email-masked]>
Date: Mon, 14 May 2007 17:15:12 -0400

> Here are the main changes/additions:

The deltas look good.  Thanks.

--John

---

From: "John G. Scudder" <[email-masked]>
Date: Mon, 14 May 2007 17:23:38 -0400

> The reference for growth could be Geoff Hustons http:// 

I think a reference needs to be more specific than just the potaroo  
URL.  I looked around a little there and didn't find anything that  
seemed citable regarding long-term per-prefix instability trends.

Someone also mentioned (on the last call?) that per-prefix  
instability may not be increasing once the top few bad actors are  
filtered out.  That would be a fairly interesting datum to validate  
or refute.

--John

---

From: "John G. Scudder" <[email-masked]>
Date: Mon, 14 May 2007 17:25:59 -0400

> I would just remove inbound. Just say inter-AS, we can do this without

As Jason observed, it's not loss of generality that would be the  
problem, but loss of specificity. :-)  Speaking as the guy who was  
asking for a more detailed definition of "TE" I kinda like it that  
way.  The document would still be OK w/o it, though.

--John

---

From: "vijay gill" <[email-masked]>
Date: Mon, 14 May 2007 14:38:03 -0700

> way.  The document would still be OK w/o it, though.

Ok, I was thinking how TE for inbound also affects TE for outbound for
transit isps (verio being a particularly good example), but I don't
have any major issues with leaving it as is either.

/vijay

---

From: "vijay gill" <[email-masked]>
Date: Mon, 14 May 2007 14:42:56 -0700

> filtered out.  That would be a fairly interesting datum to validate
The specific data are in http://bgpupdates.potaroo.net/instability/bgpupd.html
Older data are presented in
http://www.caida.org/publications/presentations/nanog0202/index.html

irl.cs.ucla.edu/papers/globecom2005.ppt

and

www.potaroo.net/presentations/2006-10-11-bgpupdatereport.ppt

/vijay

---

From: "John G. Scudder" <[email-masked]>
Date: Mon, 14 May 2007 18:15:28 -0400

> The specific data are in http://bgpupdates.potaroo.net/instability/ 

Right, but only 2 weeks worth -- not enough to draw conclusions.

> http://www.caida.org/publications/presentations/nanog0202/index.html

Interesting but again, doesn't analyze stability over time (and  
focuses on other things).

> irl.cs.ucla.edu/papers/globecom2005.ppt

OK.  If I'm reading this correctly, it seems to indicate that the  
absolute number of "highly active" prefixes observed was roughly  
constant over three years, which means it has been going *down* as a  
percentage of table size.  (This is spelled out on slide 9... along  
with the notation "I thought we agreed to remove this slide", hmm.)

This doesn't quite lend itself to the generalization that mean prefix  
stability is getting better (or worse) though.  At least, I think a  
few more steps in the logical chain would be required.

> www.potaroo.net/presentations/2006-10-11-bgpupdatereport.ppt

Again, not enough of a time series.

Geoff probably does have the data required, though -- just needs to  
show multiple years worth.

--John

---

From: "vijay gill" <[email-masked]>
Date: Mon, 14 May 2007 17:19:56 -0700

> Right, but only 2 weeks worth -- not enough to draw conclusions.

but he has archives for a period of time. We can probably ask for a
timeline over a few years to decisively settle the question. If the
answer is highly active prefixes as a percentage keep going down, then
perhaps we don't need to worry about routing table resource
consumption side at all, and stick with just computer science
techniques to scale the forwarding side.

/vijay

---

From: "John G. Scudder" <[email-masked]>
Date: Mon, 14 May 2007 20:27:35 -0400

On May 14, 2007, at 8:19 PM, vijay gill wrote:
> timeline over a few years to decisively settle the question.

We can and should.  But getting back to the original point that  
spawned this tangent (it was the question of what reference to cite),  
I know of nothing currently citable.

--John

---

From: Jason Schiller <[email-masked]>
Date: Tue, 15 May 2007 11:12:20 -0400 (EDT)

> filtered out.  That would be a fairly interesting datum to validate

I was specifically thinking of a PPT Geoff gave to GROW in March 2006.

http://www3.ietf.org/proceedings/06mar/slides/grow-3.pdf

you can skip to slide 15.. thats where the stuff on updates and
widthdrawals starts.  

Slide 18, over 2005 the number of updates has doubled, number of prefixes
per update are falling.

Slide 32, the projections based on 2005 numbers.

Slide 35 starts in on the uncertainty factor.  

Slide 53 has the conclusion about the uncertainty factor:
"It would appear that the BGP update rate is being strongly biased by a
small number of origins with two forms od behaviour:
 - Traffic Engineering - consistent updates rates sustained over weeks /
   month with a strong component of first hop change and persistent
   announce and withdrawal of more specifics.

- Unstable configuration states - a configuration which cannot stabilise
and for a period of hours or days the update rate is extremely intense."

Not sure if there is a regular report on this... Haven't had a change to
poke arount at potaroo for one.

__Jason

On Mon, 14 May 2007, John G. Scudder wrote:

> Date: Mon, 14 May 2007 17:23:38 -0400
> From: John G. Scudder <[email-masked]>
> To: vijay gill <[email-masked]>
> Cc: Thomas Narten <[email-masked]>, [email-masked]