Disabling IPv6 Doesn't Help
Hola. Bonjour. Speaking a second language can be very helpful – it allows you to communicate in situations where you otherwise wouldn’t be able to. Some skilled linguists are fluent in six or seven languages, really maximizing their communication possibilities.
Do you think that people who speak multiple languages start up each and every conversation by trying every language they speak until they hit on the right one? It wouldn’t be very optimal to start every conversation with your spouse or boss speaking in Farsi, then French, then Japanese, then English. This “try everything” method of communication could definitely slow down your daily communication, which is why multi-lingual speakers don’t use it.
Instead they look for clues in their environment and from the person they are speaking with to determine which language to speak – this allows communication without slowing them down by trying each language every time.
For some reason, people think that Vista isn’t smart enough to do this. Since Vista has IPv6 enabled by default, many people are recommending that IPv6 be disabled because they think it will speed up their web browsing since most web sites aren’t using IPv6 addresses yet. It turns out that it isn’t helping, though, because IPv6 isn’t the issue.
Take a look at some of these links for some of the reports I am talking about. Look for IPv6 on these pages and you will see what I mean.
http://www.vistax64.com/vista-general/65116-vista-network-performance-again.html
http://windows.edu.pl/vista-44219.html
https://channel9.msdn.com/ShowPost.aspx?PostID=295759
http://www.pcreview.co.uk/forums/thread-3016687.php
So how does Vista deal with multiple protocols?
When you first turn your computer on, Vista tries to get an IPv4 and IPv6 address by default. You are not providing it an IPv6 address, so it provisions an IPv4, an IPv6 link-local, and possibly a Teredo address.
Most everything on the Internet is still IPv4, so when you do your normal “stuff” on the Internet, you are always using IPv4. It isn’t trying to use IPv6 first, nor is it trying to use Teredo. This means that you aren’t doubling the amount of packets going out, and IPv6 is basically just sitting there quietly.
If you happen to go to a website that has both IPv4 and IPv6 records registered in DNS, your Vista machine would still use IPv4 to go to the website with no double traffic. Why? Because the TCP/IP stack knows that is can’t use IPv6 (since it doesn’t have a globally routable IPv6 address) so the DNS resolver never even asks for the AAAA (which is the IPv6) record. In other words, if your Vista machine can’t use IPv6, it doesn’t LOOK for IPv6 on the Internet! (Pretty neat, huh?)
At no point in this exercise has your machine ‘doubled the traffic” or brought down unnecessary data. In other words, IPv6 doesn’t slow down your Internet browsing.
2. Accessing local network devices
So you have a network printer that you are having problems accessing, and you think IPv6 is getting in the way? It's not. When you want to talk to a network device that is on-link, your Vista machine will see that the printer is connected to the network using an IPv4 address, perform a quick subnet comparison of its IPv4 address and the printer’s to determine that they are on the same subnet, and then use the MAC address of the printer for all future communication.
IP addresses (whether v4 or v6) are just used to help packets get from one network to another; the MAC addresses do all of the local communication once on-link. In this case, the IPv6 address of the Vista machine is ignored since the printer only supports IPv4.
3. Other Stuff
IPv6 just doesn't cause stop errors (a.k.a Blue Screens of Death), program crashes, global warming, bad hair days, or that annoying talking lizard on the commercials. That is all just OBSNDRTIPV6 (Other Bad Stuff Not Directly Relatable to IPv6).
IPv6 was subjected to a rigorous testing process and security review before we allowed Windows Vista and Windows Server 2008 to ship with it enabled and preferred. We believe this is the safest, most expedient method of gaining widespread IPv6 adoption in the marketplace, but we ensured that in doing so we would not impact your end user experience.