Subject: Re: NATs *ARE* evil!

From: "J. Noel Chiappa" <[email-masked]>
Date: Sun, 17 Dec 2000 12:37:39 -0500

> From: Bradley Dunn <[email-masked]>

    > I do think that there is a definite causal relationship between the
    > address space shortage and the number of prefixes in the routing tables.
    > People who allocate addresses .. use slow-start algorithms in their
    > allocation policies due to the shortage of addresses. Therefore many
    > organizations end up announcing several non-aggregatable prefixes ..
    > .. If everyone could get "enough" addresses the first time, we'd be
    > much closer to the ideal of one prefix per AS.

You do have a valid point - that the address shortage is causing people to
have multiple prefixes.

However, do realize that when you do an O(N) analysis on the various factors
that are causing the growth in the routing table, this particular one is
causing more of an O(C) factor (since most organizations with more than one
prefix would have a reasonably limited number of them), or maybe
O(growth-rate-of-individual-organization) [which in most cases is going to be
pretty small - ISP's adding a lot of customers would be one exception]. In
other words, the exponential shape of the routing table size cannot be due to
an O(C) or O(average-growth-of-individual-organization) factor.

The bulk of the growth in the table has to be due to the growth in the
network population as a whole, i.e. the sheer number of organizations
attached to the network (which is growing at a much faster rate than any
individual organization) - and in particular those which are becoming
multi-homed.

It's hard to put numbers on it without knowing what %-age of sites which are
already globally advertised has more that one prefix, and how fast that
number is growing. However, looking at the routing table growth (it has
doubled in about 3 years), and given the growth in the user community over
that time, one has to expect that the growth in the user community is the
driver.

Yes, the point you mention will have put something of a multiplier on the
table size - but it's a relativly static multiplier, I expect.

	Noel

---

From: Bradley Dunn <[email-masked]>
Date: Sun, 17 Dec 2000 15:13:51 -0800

>that time, one has to expect that the growth in the user community is the

This is probably true. The data seem to support it. The increase in 
prefixes due to stingy allocation policies apparently has been more than 
cancelled out by the decrease in prefixes (presumably) due to better 
aggregation.

The number of prefixes per AS has been trending downward:
http://www.telstra.net/ops/bgp-entries-as.html
while the number of ASes has been increasing:
http://www.telstra.net/ops/bgp-as-count.html

Bradley