was bogon filters, now "Brief Segue on 1918"

michael.dillon at bt.com michael.dillon at bt.com
Thu Aug 7 12:06:29 CDT 2008

>Your point seemed to be that 
> it is not a large enough allocation of IPs for an 
> international enterprise of 80K souls.  My rebuttal is: 16.5 
> million IPs isn't enough?

You don't seem to understand how IPv4 networks are designed 
and how that interacts with scale, i.e. the large sprawling
networks that international enterprises have. You don't simply
count out x addresses per employee. Instead, you design a subnet
architecture that a) can grow at all levels, and b) can be
cut off the network when you sell off a branch operation or two.

This leads to large amounts of IP addresses used up in padding
at all levels, which then leads to these organizations running
out of RFC 1918 space, a more and more common occurence. This,
in itself, is a good incentive to move to IPv6, since the
seemingly wasteful subnet architecture is considered best practice
with IPv6, and a ULA prefix or two gives you lots of space to
keep growing.

>  What are we talking 
> about then?  100 IPs per person--say each person has 10 PCs, 
> 10 printers, 10 automated factory machines, 10 lab 
> instruments, 49 servers and the soda machine on their 
> network? 

Nope. We are not talking about people, but about network
architecture and topology. Two people in one office need
two addresses. Put them in separate offices and they need
two subnets. Topology dominates the design.

> I don't think you have that many soda 
> machines.  Even on 5 continents.  Even with your growing 
> Asian market, your suppliers, and the whole marketing team.

I believe the first two companies to run out of RFC 1918
space (or to project that it would happen) are Comcast,
and American cable provider in one continent, and a
Japanese cable provider on a small Pacific island next
to China.

> //Err.  Doing it wrong does not justify doing it wrong.

Cute sound bites does not make you an expert in anything.

In any case, IPv4 is yesterday's news. Nowadays everyone is
scrambling to integrate IPv6 into their networks and shift
services onto IPv6.

--Michael Dillon

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