[ppml] Solicing comments: IPv4 to IPv6 Migration IncentiveAddress Space

William Herrin arin-contact at dirtside.com
Wed Jun 27 10:55:07 EDT 2007

On 6/27/07, Howard, W. Lee <Lee.Howard at stanleyassociates.com> wrote:
> >  Since IPv6
> > addresses are 4 times the size of IPv4 addresses, that would
> > increase the memory demand on routers by a factor of 4. A
> > factor of 5 if you consider that they also have to maintain
> > the IPv4 table.
> "2 to the 64th power" is significantly more than
> "4 times (2 to the 32nd power)."
> There are roughly 4 billion addresses in IPv4.
> There are roughly 18 quintillion subnets in IPv6.
> 18,000,000,000,000,000,000 > 4*4,000,000,000


The question was: how would this proposal impact the routing table. In
the worst case scenario, this proposal would place the same number of
routes in the IPv6 table that are presently in the IPv4 table: roughly

The amount of memory necessary to list every possible subnet in IPv6
is not at issue and not relevant to the discussion.

On the other hand, my math was in error. Because the IPv6 subnet size
is fixed at /64 by the standard, routers need never consider or store
the last 8 bytes of the route. Accordingly, the IPv6 route table in
the worst case scenario need only consume twice the memory of the IPv4
table, not 4 times as much.

Bill Herrin

William D. Herrin                  herrin at dirtside.com  bill at herrin.us
3005 Crane Dr.                        Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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