BBC does IPv6 ;) (Was: large multi-site enterprises and PI

Sat Nov 27 17:25:52 UTC 2004

On 27-nov-04, at 17:43, Paul Vixie wrote:

> those of us who prefer static assignment + dhcp6 over EUI64 find a /64 
> to
> be an obscene waste of address space on a per-lan (or per-vlan) basis, 
> but
> sadly there are already some cool wireless gadgets whose idea of ipv6 
> does
> not include either static or dhcp6 addressing, so there's some tension.

> my house has four vlans (core, family, guest colo, and wireless) -- so 
> in
> the cisco home networking model i'd need a /62 for fewer than 50 hosts?

While IPv6 is still IP, it's not just IPv4 with bigger addresses. We 
have 128 bits, so we should make good use of them. One way to do this 
is to make all subnets and 99% of end-user assignements the same size. 
Yes, this wastes bits, but the bits are there anyway so not wasting 
them really doesn't buy you anything at this point. The advantage of 
having a fixed /64 per subnet is that one size fits all: there is no 
need to worry about the subnet size when designing the network, 
whatever happens, all hosts that you'll ever want to put in this subnet 
will fit in it. Always having a /48 has a similar benefit: if you ever 
need to renumber, you only need to do a search and replace on the top 
48 bits, the internal addressing structure can remain the same.

In a parallel universe IPv6 could have 64 bit addresses, saving 16 
bytes of overhead per packet (so the additional overhead re IPv4 would 
only be 4 bytes rather than 20), but here in the universe we're all 
most familiar with, this ship has sailed a long time ago.

> i life fred's reasoning.  companies with size and qualifications like
> cisco's should qualify for an ASN and for PI space.  all the world's 
> not
> a home-DSL or home-cable or isp-colo network.  routing shouldn't always
> follow addressing.  we'll need to discover a workable equilibrium 
> unless
> we want to encourage NAT in IPv6 the same way we (passively) 
> encouraged it
> in IPv4.

All I hear is how this company or that enterprise "should qualify" for 
PI space. What I don't hear is what's going to happen when the routing 
tables grow too large, or how to prevent this. I think just about 
anyone "should qualify", but ONLY if there is some form of aggregation 
possible. PI in IPv6 without aggregation would be a bigger mistake than 
all other IPv6 mistakes so far.