[LINK] IPv4 host density measured by ping

Glen Turner glen.turner at aarnet.edu.au
Thu Mar 1 06:31:59 AEDT 2007

Hi Robin,

Here is our forthcoming advice to IT managers on IPv4 exhaustion.


There are fifty unallocated /8 IPv4 networks remaining. Ten of these
are being allocated each year.  IPv4 address space will become scarce
during the lifetime of equipment being purchased today.  IT managers
should develop strategies to avoid a crisis caused by IPv4 address

The currently-proposed APNIC policy for address space exhaustion is to
reserve a few /8s but otherwise continue with its current policies. In
particular, the current policies that discourage a secondary market in
IPv4 addresses are proposed to remain.

Scarcity of IPv4 addresses will increase the use of IPv6. Prudent IT
managers will ensure that current purchases have IPv6 support of a
quality equivalent to the product's IPv4 support. If the product does
not support IPv6 then IT managers should seek a firm commitment for
future IPv6 support.

The quality of IPv6 support should be probed. Many vendors support
IPv4 in hardware but IPv6 in software. This is not suitable when large
increases in IPv6 traffic may be expected during the life of the

AARNet has seen many access lists which prevent access over IPv4 but
allows access over IPv6. It appears that system administrators and
network engineers do not consider IPv6, even though IPv6 is turned on
by default in the current versions of Windows, MacOS and Red Hat
Linux. IT managers should insist that the need for an IPv6 access list
is investigated whenever an IPv4 access list is created.

Scarcity of IPv4 address space will increase the use of network address
translation. Prudent IT managers will ensure that relevant current
purchases have NAT support of good quality.

It is likely that applications delivered today will be in service when
IPv4 address exhaustion occurs.  Applications acceptance testing
should include testing of interoperation with the server and client
running IPv6 and interoperation with the client is behind a network
address translation gateway.

IT managers of institutions which have been allocated a /16 (a
historical class B) should not feel complacent. Requests for
additional address space require 90% of the current allocation to be
used. So it may not be possible for holders of a /16 to obtain small
address blocks for, say, an overseas campus.  The holder of the /16
may need to renumber their main campus into a /17 to be able to make a
small allocation out of the remaining /17.

A request for an IPv4 allocation by APNIC may trigger an audit by
APNIC of the institution's current use of address space. The likely
result being that the /16 allocation may be replaced by a more
appropriate allocation.

The coming scarcity of IP address space allocations will bite hardest
in the areas served by APNIC. IT managers may anticipate an
increasingly rigid observance by APNIC of its rules and procedures.

IT managers should consider the end-game, which despite current
proposals may not occur with the current APNIC policies. Perhaps a
regulated secondary market for IPv4 addresses will develop and IT
departments may be asked by their institution to grasp this
windfall. Or perhaps use charges per IP address will occur in an
effort to apply market forces to conserve the remaining unused
address space, in which case an underused /16 may be prohibitively

IT managers should encourage IT practices which simplify the
implementation of IT policies addressing IPv4 address exhaustion. For
example, deploying dynamic DHCP and dynamic DNS as widely as possible;
minimising applications' knowledge of the host's IP address; deploying
IPv6-aware applications and operating systems; encouraging
applications to use authentication rather than access control based on
IPv4 addresses.

Doubtless scams will occur, so it will become even more prudent to use
strong authentication to secure address allocation details in the
APNIC registry. Historic allocations which do not have an entry in the
APNIC registry should create a registry entry.

There are two major papers addressing address space exhaustion. Reading
Tony Hain's paper and its following discussion is highly recommended.
Both papers agree that IPv4 address space will be exhausted within the
next four to nine years. Geoff Huston has additional papers and data at


Tony Hain.
A pragmatic report on IPv4 address space consumption.
Internet Protocol Journal. Cisco Systems. Vol 8, no 3, September 2005.

Geoff Huston.
IPv4: How long do we have?
Internet Protocol Journal. Cisco Systems. Vol 6, no 4, December 2003.

Copyright (C) AARNet Pty Ltd (), 2007.

 Glen Turner         Tel: (08) 8303 3936 or +61 8 8303 3936
 Australia's Academic & Research Network  www.aarnet.edu.au

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