IPv6 feature in Network Adaptor is Slowing Internet

Question

The past few days, my internet browsing has become very poor. It's not a matter of speed, as a speed test will give at least 15Mbps. It seems as if my laptop has a hard time actually connecting to the sites.

I've found a possible culprit, but don't know why it would affect anything:

Going to adapter settings and disabling ipv6, but leaving ipv4, my browsing is back to normal. Re-enabling ipv6 brings back the issue. This is strange though, because I have always had ipv6 enabled. Moreover, using sites to test ipv6 compatibility, I fail with ipv6 enabled on my adapter, and pass when it's disabled.

Ideas about why this is happening, and how to fix it?

Answer 1

If you have IPV6 turned on, DNS lookups are 2 to 3 times slower than with IPV4. That's why it seems as if your computer has "trouble connecting" to web sites. When you initiate a connection to any site, the first thing it does is look up the IP address in DNS.

DNS lookups are slow on IPV6 for several reasons.

First, DNS is currently handled in serial, not parallel. The IPV4 lookup is always handled first, then the IPV6, so it takes at least twice as long.

Second, because the IPV6 lookups are less frequent, they are not cached as often on the DNS server, causing further delay.

This is what makes it seem like it takes sites longer to start loading when IPV6 is enabled, because they do take longer to start loading! Also, keep in mind that most web pages load content from many different URL's, and every time the browser has to look up an address for an image, Flash object, or anything else on the page, the slowdown on the page is increased.

There's nothing you can do in your operating system to speed this up. It affects all operating systems including Windows, Mac, and Linux

It's best to disable IPV6 for now, unless you have a specific requirement for it (almost no one does)

Answer 2

Just leave IPv6 disabled. You are not likely to use it for a while, and right now, your computer is looking for non-existent IPv6 things, especially DNS but possibly other things, and retrying them until they timeout. Those timeouts are what are slowing you down.

Answer 3

You can try disabling the 'autotuning' function of win7 and vista in TCP/IP On command prompt you verify if 'autotuning' is on with

Netsh interface tcp show global 

if 'Receive Window Auto-Tuning Level' = normal then give the command:

Netsh interface tcp set global autotuning=disabled

The above fixed my sudden slow performance issues of win7 with ipv6 enabled.