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networking - IPv4 vs IPv6 priority in Windows 7


I have IPv6 connectivity through Hurricane Electric tunnel. Since IPv6 day this year, many services (google.com, facebook.com, etc.) enabled IPv6 on their main domains. On my Windows machine, IPv6 is preferred over IPv4. This means that whenever I visit Google, all traffic goes through my tunnel to Hurricane Electric, which raises the latency by more than 100%:


C:\> ping www.google.com

Pinging www.l.google.com [2001:4860:8005::68] with 32 bytes of data:
Reply from 2001:4860:8005::68: time=85ms
Reply from 2001:4860:8005::68: time=84ms
Reply from 2001:4860:8005::68: time=112ms
Reply from 2001:4860:8005::68: time=86ms

Ping statistics for 2001:4860:8005::68:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 84ms, Maximum = 112ms, Average = 91ms


C:\> ping -4 www.google.com

Pinging www.l.google.com [173.194.79.103] with 32 bytes of data:
Reply from 173.194.79.103: bytes=32 time=28ms TTL=48
Reply from 173.194.79.103: bytes=32 time=28ms TTL=48
Reply from 173.194.79.103: bytes=32 time=55ms TTL=46
Reply from 173.194.79.103: bytes=32 time=29ms TTL=46

Ping statistics for 173.194.79.103:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 28ms, Maximum = 55ms, Average = 35ms

Question: How can I make Windows 7 to always prefer IPv4, when both IPv4 and IPv6 records are available for a specific domain name?



Answer



Solution #1: Add a prefix policy to prefer IPv4 addresses over IPv6


Prefix policy table is similar a routing table, it determines which IP addresses are preferred when making a connection. Note that higher precedence in prefix policies is represented by a higher "precedence" value, exactly opposite to routing table "cost" value.


Default Windows prefix policy table:


C:\> netsh interface ipv6 show prefixpolicies
Querying active state...

Precedence  Label  Prefix
----------  -----  --------------------------------
        50      0  ::1/128
        40      1  ::/0
        30      2  2002::/16
        20      3  ::/96
        10      4  ::ffff:0:0/96
         5      5  2001::/32

Note that IPv6 addresses (::/0) are preferred over IPv4 addresses (::/96, ::ffff:0:0/96).


We can create a policy that will make Hurricane Electric IPv6 tunnel less favorable than any IPv4 address:


netsh interface ipv6 add prefixpolicy 2001:470::/32 3 6

2001:470::/32 is Hurricane Electric's prefix, 3 is a Precedence (very low) and 6 is a Label.


I could have used a more generic prefix, but I wanted to make sure that if and when I get direct IPv6 connectivity from an ISP, it will take precedence over IPv4.


If you adapt this solution, you need to substitute an appropriate IPv6 prefix instead of my Hurricane Electric one.


Solution #2: Tweak registry to make Windows always prefer IPv4 over IPv6


This solution is more generic, but more invasive and less standards-compliant. In the end, Windows will still modify the prefix policy table for you.



  • Open RegEdit, navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\tcpip6\Parameters

  • Create DisabledComponents DWORD registry value, set its value to 20 (Hexadecimal). See Microsoft KB 929852 for more info about this registry key, especially if DisabledComponents already exists on your system.

  • Reboot.


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