Re: Why is IPv6 faster?
> Is it faster for connection setup/teardown? Is it able to sustain faster throughput? Or are the higher layer protocols doing something different when on an IPv6 base to account for this?
The real reason is complex, but interesting - and for some reason doesn't seem to be discussed much in public.
Try comparing the output of "traceroute" and "traceroute6" to the same destination, and you'll see that often the traffic takes completely different paths. Even if it doesn't in the forward direction, it may well in the reverse.
Essentially, the IPv4 and IPv6 Internets are *two entirely separate networks*. Not only do they have their own protocols and numbering plans, they also have distinct topologies: some networks peer on IPv4 but not on IPv6, or vice versa. They really are ships that pass in the night.
Now, for a long time one particular provider - one who also offers IPv6 tunnel services - has been trying to position themselves as a Tier 1 on IPv6 (a Tier 1 being a network which only peers with other networks, and does not pay for transit anywhere). To try to achieve this, they have been offering free IPv6 peering to pretty much every network at every exchange point, in order to collect lots of routes and make themselves an attractive peering partner to the other Tier 1's.
The net result is that to reach certain networks your IPv6 traffic may go straight onto this provider's backbone from A to B, rather than going via A's transit provider and then B's transit provider via some intermediate peering point.
This is clearly not a sustainable proposition - eventually this provider is going to have to have paying transit customers rather than giving free transit to both A and B. Also, to achieve Tier 1 it will have to get all the other Tier 1's to peer with it, which was proving difficult: at one point they even offered them cake (Google for "hurricane electric peering cake")
So the upshot is: short term, IPv6 may be faster because some traffic may be using a different backbone for IPv6 than IPv4. Long term, this anomoly will vanish; IPv6 will then be slightly slower, because of the larger headers (40 bytes compared to 20 bytes)