10.4. Configuring Preference for Link-Local Addresses

The destination address selection rules give preference to destinations of smaller scope. For example, a link-local destination will be sorted before a global scope destination when the two are otherwise equally suitable. An administrator can change the policy table to reverse this preference and sort global destinations before link-local destinations:

   Prefix        Precedence Label
   ::1/128               50     0
   ::/0                  40     1
   ::ffff:0:0/96         35     4
   fe80::/10             33     1
   2002::/16             30     2
   2001::/32              5     5
   fc00::/7               3    13
   ::/96                  1     3
   fec0::/10              1    11
   3ffe::/16              1    12

This change to the default policy table produces the following behavior:

Example 1:

• Candidate Source Addresses: 2001:db8::2 or fe80::2
• Destination Address List: 2001:db8::1 or fe80::1
• New Result: 2001:db8::1 (src 2001:db8::2) then fe80::1 (src fe80::2) (prefer higher precedence)

Example 2:

• Candidate Source Addresses: 2001:db8::2 (deprecated) or fe80::2
• Destination Address List: 2001:db8::1 or fe80::1
• Unchanged Result: fe80::1 (src fe80::2) then 2001:db8::1 (src 2001:db8::2) (avoid deprecated addresses)