BBC News - 'Fresh proposals' planned over cyber-monitoring

[Ian Batten]

On 13 May 2013, at 10:09, Andrew Cormack <Andrew.Cormack at ja.net> wrote:

>  Doesn't mapping v4 addresses into part of the v6 space mean that the v6 table has to be at least as big as the v4 one from day one?

Well, for some value of "at least as big".  If, for example, you have an IPv4 default route, then ::ffff/96 only has one route.  If you have a sparse set of routing tables for IPv4, then ::ffff/96 will have exactly as many routing entries as there are v4 routes.

And in any event, a fully populated IPv4 routing table with a separate forwarding entry for every /32 --- which is much, much denser than reality --- only requires 16GB of RAM.  In the context of core routers, that's neither here nor there, and becoming less here and less there with every passing day.  

ian