Shim6 vs PI addressing

Thus spake "Iljitsch van Beijnum"
<iljitschmuada.com>
> On 1-mrt-2006, at 18:05, David Barak wrote:
>> Is it easier to scale N routers, or scale 10000*N
hosts?
...
> 2 x relatively small is a lot less than 10 x relatively
large. Or, in 
> other
> words: on the host you only pay if you actually
communicate. In
> routers, you pay more as there is more routing
information, whether
> the extra information is used or not.

OTOH, hosts go a lot longer between upgrades and generally
don't have 
professional admins.  It'll be a long, long time (if ever)
until shim6 is 
deployed widely enough for folks to literally bet their
company on 
host-based multihoming.

>> If we simply moved to an "everyone with an
ASN
>> gets a /32" model, we'd have about 30,000
/32s.  It
>> would be a really long time before we had as many
>> routes in the table as we do today, let alone the
>> umpteen-bazillion routes which scare everyone so
>> badly.
>
> 1. We've already walked the edge of the cliff several
times (CIDR had  to 
> be implemented in a big hurry, later flap dampening and
prefix  length 
> filtering were needed)

At least this time we know what the likely problems are, and
we can build in 
safeguards that can be quickly implemented if we get too
close to the edge. 
Not that I agree we'll even get there...

> 2. We'll have to live with IPv6 a long time

Perhaps.  I know the goal was for it to last 100 years, but
what technology 
has ever lasted that long without significant improvements
that altered it 
almost beyond recognition?

> 3. Route processing and FIB lookups scale worse than
linear

With an mtrie+ FIB, routing lookups scale far, far better
than linear.  What 
matters is the length of the prefix being matched, not how
many there are.

TCAMs scale linearly, provided you can build them big enough
(and costs 
certainly aren't linear).

> 4. If the global routing table meltdown happens, it
will be extremely 
> costly in a short time
> 5. Even if the meltdown doesn't happen a smaller
routing table makes 
> everything cheaper and gives us more implementation
options (5000  entry 
> TCAM is nice, 500000 entries not so much as it
basically uses  100 times 
> as much power)

Agreed.

> 6. Moore can't go on forever, there are physical
limitations

Every time folks claim that, someone makes a breakthrough
that continues the 
curve.  Surely we can't count on this forever, but so far
money has 
consistently trumped "physical limitations".

> But the most important thing we should remember is that
currently, 
> routing table growth is artificially limited by
relatively strict 
> requirements for getting a /24 or larger. With IPv6
this goes away,  and 
> we don't know how many people will want to multihome
then.

The requirements for getting a /24 are pretty darn lax,
actually, and the 
current proposals for PI space being debated within ARIN are
significantly 
more restrictive.

The reality today is that v4 routing tables are well within
our capabilities 
and growing slowly.  If we were on the verge of another
serious problem, 
like we where when the CIDR fire drill happened, ISPs could
easily cut the 
tables in half simply by filtering prefixes longer than RIR
minima.

S

Stephen Sprunk        "Stupid people surround
themselves with smart
CCIE #3723           people.  Smart people surround
themselves with
K5SSS         smart people who disagree with them." 
--Aaron Sorkin