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

Ian Batten igb at
Mon May 13 08:46:37 BST 2013

On 12 May 2013, at 15:39, Peter Fairbrother <zenadsl6186 at> wrote:

> On 12/05/13 10:07, Florian Weimer wrote:
>> * Charles Lindsey:
>>> But I thought IPv6 did reserve a batch of numbers that would map into
>>> the IPv4 space (but not at the "bottom" of the IPv6 range).
>> There are at least three different reserved /96 prefixes for mapping
>> IPv4 addresses.  Except for the deprecated ::/96 prefix, these
>> mappings are incompatible with the IPv6 address architecture and its
>> requirements on the structure of global unicast addresses, so their
>> use on the IPv6 Internet is not permitted.
> I thought the 64:ff9b prefix was routable in IPv6?

Isn't the idea that you use IPv4 embedded in IPv6 until you reach a dual-stack machine, and switch out to IPv4 at that point?  There's going to have to be some sort of NAT at that stage whatever happens, in order for the return packet to get back.

> Mind, I think IPv6 is a horrible kludge with no advantages (apart from the larger address space, which could easily be done with a small extension to IPv4) over IPv4, and should be aborted.

I simply don't understand this argument.  What is IPv6, if not IPv4 with a small extension for a larger address space (and you say that as though it's not terribly important)?  TCP and UDP go over IPv6 unchanged, for example.  Why would introducing an extension to IPv4 which would be entirely incompatible (it would require a different sized packet header, for example) by any easier than introducing IPv6?  What's the sticking point in IPv6 which makes it harder?
> Is the IPv4 240./8 range still reserved? Just start all IPv4e (IPv4 extended) addresses with that and make them 10 bytes long, it won't break much.

Aside from every single IPv4 application, router, software stack and analyser.  How do you propose, for example, dealing with every piece of code that uses sockaddr_in, every router that assumes the size of the IP header and every routing table everywhere?


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