How to Administer the IPv6 Address Selection Policy Table

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The following procedure describes how to modify the address selection policy table. For conceptual information about IPv6 default address selection, see Description of the ipaddrsel Command.

Caution - Do not change the IPv6 address selection policy table except for the reasons that are provided in the following procedure. Doing so, can cause problems on the network due to a badly constructed policy table. Also, be sure to save a backup copy of the policy table, as shown in this procedure.

Become an administrator.

Review the current IPv6 address selection policy table.

# ipaddrsel
# Prefix                  Precedence Label
::1/128                           50 Loopback
::/0                              40 Default
2002::/16                         30 6to4
::/96                             20 IPv4_Compatible
::ffff:0.0.0.0/96                 10 IPv4

Make a backup copy of the default address policy table.

# cp /etc/inet/ipaddrsel.conf /etc/inet/ipaddrsel.conf.orig

Add any customizations to the /etc/inet/ipaddrsel.conf file.
```
# pfedit /etc/inet/ipaddrsel.conf
```
Use the following syntax for entries in /etc/inet/ipaddrsel:
```
prefix/prefix-length precedence label [# comment ] 
```
See Example 1–1 for examples of some common modifications that you might make.

Load the modified policy table into the kernel.
```
# ipaddrsel -f /etc/inet/ipaddrsel.conf
```

If the modified policy table has problems, restore the default IPv6 address selection policy table.
```
# ipaddrsel -d
```

Example 1-1 Modifying the Default Pv6 Address Selection Policy Table

The following are some common modifications that you might want to make to your policy table:

Assign the highest priority to 6to4 addresses.
```
2002::/16                         50 6to4
::1/128                           45 Loopback
```
The 6to4 address format now has the highest priority, 50. Loopback, which previously had a 50 precedence, now has a 45 precedence. The other addressing formats remain the same.
Designate a specific source address to be used in communications with a specific destination address.
```
::1/128                           50 Loopback
2001:1111:1111::1/128             40 ClientNet
2001:2222:2222::/48               40 ClientNet
::/0                              40 Default
```
This particular entry is useful for hosts with only one physical interface. Here, 2001:1111:1111::1/128 is preferred as the source address on all packets that are bound for destinations within network 2001:2222:2222::/48. The 40 priority gives higher precedence to the source address 2001:1111:1111::1/128 than to other address formats configured for the interface.
Favor IPv4 addresses over IPv6 addresses.
```
::ffff:0.0.0.0/96                 60 IPv4
::1/128                           50 Loopback
.
.
```
The IPv4 format ::ffff:0.0.0.0/96 has its precedence changed from the default 10 to 60, the highest priority in the table.