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Windows IP Address Prefix Policies

The prefix policy table is the list used for selecting/sorting which IP addresses are to be used by their prefix (range of addresses).

Now there are changes needed to the default policy table per recommendations in a somewhat new standard, RFC 6724 (from 2012). It obsoletes the older standard RFC 3484 (from 2003) and both Microsoft & NTT collaborated on these updates partially because of issues with NTT's NGN deployment & partially to prefer IPv4 over some transitional IPv6 technologies among other minor things.

Step 1: Determine what to do with your Windows version
  • If you're running a clean install of Windows 8.1 or later then you don't need to change anything but you can skip to next step to make certain if you want to.
  • If you're running Windows 8 then get all the latest Windows updates (since not sure which update changes the defaults) then type 'netsh int ipv6 reset' to reset the IPv6 stack to defaults (unless you have other custom IPv6 settings you want to keep and if so then use the Vista+ script) then reboot.
  • If you're running XP, Vista, 7 or a comparable server version then I've put together a Windows Command Script (modern batch file) to update the prefix policy entries to match the latest recommendations. The script file is at the bottom of this page. You can download the whole zip file by clicking the down arrow on the right or click on the name on the left to select just the one for your version. Then run as admin to get the prefix policy table updated. The script is pretty simple so a quick look at the commands should alleviate any security concerns.
Step 2: Check current policies

For XP, type netsh int ipv6 show prefixpolicy to see current policies.
For Vista or later, type netsh int ipv6 show prefixpolicies to see current policies.

Step 3: Compare policies

A list of the old defaults compared to new ones are included below. Note that a higher precedence means a higher preference for Windows to use the prefix over the others so make sure to sort either precedence in descending order.
Showing 9 items
NamePrefixOld precedenceNew precedence
NamePrefixOld precedenceNew precedence
IPv6 loopback ::1/128 50 50 
6bone 3ffe::/16 40 01 
Native IPv6 ::/0 40 40 
site-local fec0::/10 40 01 
ULAs fc00::/7 40 03 
6to4 2002::/16 30 30 
IPv4compat ::/96 20 01 
IPv4 ::ffff:0:0/96 10 35 
Teredo 2001::/32 05 05 
Showing 9 items
Joshua Reynolds,
Jan 21, 2014, 4:38 PM