Re: [rrg] Geoff Huston's BGP/DFZ research - 300k DFZ prefixes are the tip of the iceberg

[Tom Vest <[e-mail]>]

Paul raises a critical point that IMO gets insufficient attention here... 

On Mar 15, 2010, at 3:35 AM, Tony Li wrote:

> 
> Hi Paul,
> 
>> Well, let's look at the flip-side for a moment. Imagine if there were
>> /no/ growth in prefixes. Is that good? I think the answer clearly is
>> "no". No growth in prefixes implies no growth in the internet,
>> implies no growth in revenue for those who make money from activities
>> associated with attaching to the net.
> 
> Actually, no growth in prefixes does not imply that there is no growth in
> the Internet.  You can still add customers within existing prefix
> allocations and improve your addressing efficiency.

Point of clarification: 
*Existing* (aka incumbent) providers may be able to add additional customers under *existing* prefixes.
It's not possible to assume anything beyond that without assuming facts not in evidence  -- e.g., a widely adopted new architecture, and/or a widely adopted new addressing format (IPv6), and/or a widely adopted mechanism for redistributing IPv4 address space that is already allocated.

The implication is that while this possibility may exist (for some), its existence doesn't matter (in general).

> Also, since you can grow the net very efficiently with even a tiny amount of
> prefix additions, it would seem like much, much, much slower growth would be
> acceptable to meet your reasonable request that the Internet keep growing.


It seems that the problem of "super-linear" growth in demands on the routing system is one of (if not THE) most central issues motivating this exercise. And yet the ambiguous nature of this characterization is apparent even in draft-narten-radir-problem-statement-05.txt. 

Assuming that "super-linear growth" is driven by some combination of factors like

(a) new routing service providers, plus
(b) incremental address provisioning (i.e., post-CIDR IPv4 scarcity management), plus
(c) new sites, plus
(d) multihoming, plus
(e) supplemental traffic engineering,

...any new architecture that solves this routing *inflation* problem, but in the process suppresses (a), or leaves (a) to be sorted out through exogenous mechanisms is quite likely to create the opposite problem. IMO, any network architecture that is inherently vulnerable to that other risk of routing system *deflation* -- i.e., the arbitrary rationing/structural exclusion of future aspiring routing service providers -- is unlikely to be widely adopted, and should be considered harmful, fatal. 

In short, that first factor -- new entrants into the routing services sector -- constitutes an upward-sloping growth "line" that *must* be sustained, no matter how effective or ineffective the new architecture is in eliminating the "super-linear" scalability problems caused by the other factors.


>> Let the data do the arguing. At the moment it's looking like BGP
>> maybe is coping with growth just fine. I.e. we can not yet safely
>> conclude there is an urgent scaling problem with internet routing
>> (despite path-vector being known now to have some inefficient
>> behaviours even when working as intended).
> 
> First, no one is claiming that there is an imminent and urgent problem.
> What I feel that we've shown is that we have a long term systemic problem.
> Given that truly dealing with this issue does appear to require major
> amounts of time to deploy, it only seems reasonable to start dealing with it
> long before it becomes an urgent problem.

I would argue that the exhaustion of unallocated IPv4 represents a very imminent an urgent problem, for the same reason outlined above. Given current architecture and the current state of IPv6 deployment, (a) shares fate with the availability of unallocated IPv4.

No doubt if (when) the existing mechanisms for sustaining (a) no longer work, other forces will come into play in response to the unmet demand (e.g., markets, regulation, piracy, etc.). But as a result, the base rate of new entry (a) will no longer be strongly influenced by technical scalability considerations -- and the collateral effects of those external forces could have additional, unpredictable effects on the deployability or other scalability benefits (ala b~e) of the new architecture. 


>> Where's the data suggesting routing is or is going to run into
>> problems? Not /fears/ that it will, but actual data.
> 
> Please see my RAWS presentation.  It shows that prefix growth exceeds the
> speedup that we can expect in DRAM.  This in turn implies that BGP will take
> longer to converge at a given node when that node has to process the full
> table.
> 
> Tony

I agree that premature obsolescence/abandonment and/or collapse is a real problem, but I think we should recognize that routing system inflation is just one (of at least two) paths that lead in that general direction.

TV