[arin-ppml] "Millions of Internet Addresses Are Lying Idle" (slashdot)

James Hess mysidia at gmail.com
Mon Oct 20 08:40:47 EDT 2008

On Sat, Oct 18, 2008 at 4:22 PM, Leo Bicknell <bicknell at ufp.org> wrote:
> However, the larger problem is that this is the entirely wrong
> definition of "in use".  Let's take a simple example of a University.
> They may have wired dorm rooms, students with laptops, and wifi
> enabled classrooms.  If you ping at 11AM, the classroom IP's respond,
> and the dorm ones do not, if you ping at 11PM, the dorm rooms
> respond, the classrooms do not.  And if you ping at 12 noon when
> they are all walking to lunch almost none of either respond.

It is a flawwed methodology to use ICMP / TCP pings  to detect hosts

In that case,  I would have to say the university is not using the IP
space as efficiently as possible.  And indeed the ips _aren't_  in use
when nothing is connected to them.

A study  perhaps _should_  count the extra ones used as IPs that are
being wasted.

The inefficiency results from tying up the classroom WiFi   ips at
times when these IPs are not needed at all  and tying up the dorm IPs
at times when they are not needed.

This inefficiency may result in consuming twice as many IPs as needed;
since each host
essentially has a different IP at different times of the day.

Efficient use would be to have one pool of IPs;  a laptop is assigned
an IP from a DHCP pool,
That pool is the same for both classroom WiFi  and for dorm room connectivity.
And does not change if a laptop is moved between two places on the campus net.

Logically, the IP  is a property of the host.
The reason a host would ever have different IPs  when plugged into
different parts of the same organization's  network   is that the
topology is laden with an excessive number of
Layer 3  routing devices.

Instead,  switches  and bridges  should be used to connect the   Dorm
and classroom WiFi networks.
Any   firewalling,  broadcast filtering,  traffic limits, DHCP use
enforcement,  etc,
between the two  should  all be implemented on  transparent bridges.

This  design would eliminate unnecessary duplication of IPs for the
small set of hosts.


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