North American Network Operators Group

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RE: CIDR Report

  • From: Roeland M.J. Meyer
  • Date: Sun May 14 06:08:45 2000

> Owen DeLong: Saturday, May 13, 2000 3:35 PM
> > I actually agree with you here as well. relying on infinite 
> router table growth is not a scalable strategy. We need 
> something else.
> > 
> Just a small technicality here, noone is talking about 
> infinite routing
> table growth.  There are only 4 billion (roughly) possible prefixes
> if you route every node as a /32.  While 4 billion is a large number,
> it is far from infinity.

Well, that statement was obviously not intended literally. But, since we're 
throwing around numbers ...

Simply taking addresses only, that comes out to ~16GB. At $100 per 64MB 
this is about $25,000.00US in RAM, at current retail rates (prices may 
vary by vendor). It's also about $16,000.00US of EMC disk-space. This 
means that one full table would cost about $41KUS, just to store it. 
But, what will this do to performance of such a router that's working 
in a gig-E environment? The index table to access this puppy would be 
larger than the prefix table. This could easily double the cost, say $82KUS?
Considering that I just paid $98KUS for a Cisco Catalyst 6509, I guess 
this isn't too bad. However, this is only IPv4 and it is a bunch more than
the cost of the average BGP-capable router and every router on the backbone 
would have to be upgraded. This is conservative since I have not yet allowed 
for memory structure overhead. However, code-space would be relatively trivial,
even Microsoft wouldn't be able to bloat it enough so anyone else would notice.

> If you believe the IPv4 will continue for many years to come, then
> the set of possible routes is very finite.

Yes, RAM and Disk prices are also plummeting daily. By next year, we may even 
be able to afford it. We just have to figure out whose budget it comes out of. 
(How many BGP4 routers are there?)

> Of course, the number for IPv6 is much larger in theory, but when you
> consider that the last 6 octets are reserved for the MAC address
> (essentially), that leaves 80 bits, which is
> 1,208,925,819,614,629,174,706,176.  Again, a large number, but,
> far from infinity.  When you further consider that on the backbone,
> only the first eight octets are at all likely to be significant
> for routing, you come to 18,446,744,073,709,551,616 prefixes,
> which is still a large number, but even further from infinity.

Let's see here ... that's 18,446,744T 6-byte addresses? That comes 
out to 110,680,464TB. Whoops! my calculator just slipped into the 
bankruptcy zone... $172.9TUS, for RAM and $110.0TUS, for DASD. In 
addition, you'd need something just a hair short of a Cray to 
process it.

> In my opinion, eventually, we will need to find a way that each
> organizational unit is issued a portable, non-renumberable prefix
> which stays with that organizational unit.  Some larger
> organizational units may need additional prefixes, depending on
> the size of the suffix.
> Generally, it follows that most strategies for aggregating such
> prefixes will tend towards entropy as organizational units change
> their topological relationships with other organizational units.
> Thus, the only way to preserve aggregation is to make the prefixes
> issued to organizational units a function of their topology, and
> force renumbering.  While this is a simple matter for topologies
> which involve only two organizational units as neighbors, it
> becomes n! (n factorial) complex for organizational units which
> have n neighbors.  Even with IPv6, I do not believe such a
> prefix numbering scheme is practical.

Like I said, we need to do something different. The reason that I 
wrote off routing table increases is not the calculus that I just 
demonstrated, although that is an effector. It is the general concept 
that there are practical limits to that approach (there be walls, there).
In an IPv6 environment, that approach is simply unaffordable, with 
present tech. Although, it would definitely stop-gap the problem, in 
an IPv4 environment. Who will volunteer the cost of the first one of 
these routers? At that cost factor, how long do you think it will 
take to deploy them?