[ppml] IPv6 flawed?

Iljitsch van Beijnum iljitsch at muada.com
Thu Sep 6 13:30:19 EDT 2007

On 6-sep-2007, at 3:30, David Conrad wrote:

> According to <http://www.conference.sanog.org/slides/conference/
> sanog10-pfs-deaggregation-report.pdf>, we're seeing the
> "deaggregation factor" increase "slowly and steadily since 'records
> began'", with the fastest growth occurring in the "new" Internet (the
> graph on page 15 is very interesting).

Note that this is "prefixes with maximum achievable aggregation" vs  
"currently seen prefixes". If you count the number of prefixes per  
AS, you'll be getting the same number for a good number of years: 8.

> Since IPv6 uses the same
> routing and traffic engineering technology as IPv4, I am curious what
> constraints could be put in place to keep PI space down to about 1
> per ASN.

Prefixes per AS aren't limited by routing technology (if only it  
could...) so this is irrelevant. Traffic engineering also seems to be  
largely irrelevant as inspection of the routing table (without tools,  
so I might be overlooking SOME stuff but believe me, this is obvious)  
shows multiple prefixes sourced from the same AS to have the same  
attributes almost all the time.

> Perhaps more distressingly, if you believe the post IPv4 run out
> world is going to be awash with long prefixes taken from holders of
> legacy space as IPv4 address space is used more efficiently after
> free pool run out, the deaggregation factor of the "old" Internet is
> likely going to ramp up quite quickly.  This would seem to imply IPv6
> could get strangled long before it could take off, regardless of RIR
> allocation policies.

I don't see how those IPv4 issues carry over into IPv6, but to get  
back to the main point: in IPv6, you'll be either getting a /32 or a / 
48 as a PI block. So unless you manage to get multiple PI blocks, any  
efforts to inject more than a single prefix will easily be thwarted  
by prefix length filters.

That is, of course, until the people who have been pushing for PI in  
IPv6 notice that having a single, undeaggregatable IPv6 prefix means  
that they have to carry traffic between their different offices on  
their own dime, and there will be a push for multiple PI blocks per  
AS or multiple ASes per organization. Estimating the impact of that  
on routing scalability is left as an exercise for the reader.

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