v6 & DSL / Cable modems [was: Private use of non-RFC1918 IP space (IPv6-MW)]

Paul Jakma paul at jakma.org
Fri Feb 6 10:26:30 UTC 2009

On Thu, 5 Feb 2009, Matthew Moyle-Croft wrote:

> DHCP(v6).  Setting the idea in people's heads that a /64 IS going 
> to be their own statically is insane and will blow out provider's 
> own routing tables more than is rational.

Routing table size will be a function of the number of customers - 
*not* the prefix length assigned to them (for so long as address 
space is sufficiently sparsely allocated that there's a 1:1 mapping 
from customer to prefix - which should be "for a long time" with 

So (within that longer term constraint) it doesn't matter if you're 
allocating your customer a /48, /56 or /64.

Indeed, what you're suggesting - smaller-than-64 allocations - 
*would* increase routing table sizes. With your proposal those 
indexes would increase greatly in depth (and possibly other space 
increases due to not being able to optimise for "hierarchical routing 
of bits past 64 is highly rare").

Think of IPv6 as a 64bit network address + host address. At least for 

Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
If you don't have a nasty obituary you probably didn't matter.
 		-- Freeman Dyson

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