ipaddrsel(1M) System Administration Commands ipaddrsel(1M)NAMEipaddrsel - configure IPv6 default address selection
SYNOPSIS
/usr/sbin/ipaddrsel
/usr/sbin/ipaddrsel -f file
/usr/sbin/ipaddrsel -d
DESCRIPTION
Use the ipaddrsel utility to configure the IPv6 default address selec‐
tion policy table. The policy table is a longest-matching-prefix lookup
table that is used for IPv6 source address selection and for destina‐
tion address ordering when resolving names to AF_INET6 addresses. For a
description of how the policy table is used for source address selec‐
tion, see inet6(7P). For a description of how the policy table is used
for destination address ordering, see getaddrinfo(3SOCKET).
The unmodified policy table is valid for all typical IPv6 deployments.
Modify the table only if a circumstance exists for which the default
behavior of the IPv6 source address selection or destination address
ordering mechanism is unsatisfactory. See the section for examples of
such circumstances. You should carefully consider your addressing
strategy before you change the table from the provided default.
When the ipaddrsel command is issued without any arguments, the address
selection policy currently in use is printed. The format of the output
is compatible with the format of the configuration file that the -f
option accepts.
Note -
If the usesrc subcommand to ifconfig(1M) is applied to a particular
physical interface, the selection policy specified by usesrc over‐
rides the source address selection policies specified by ipaddrsel.
This is true for packets that are locally generated and for applica‐
tions that do not choose a non-zero source address using
bind(3SOCKET).
The Configuration File
The configuration file that the -f option accepts can contain either
comment lines or policy entries. Comment lines have a '#' character as
the first non-blank character. and they are ignored by the ipaddrsel
utility. Policy entry lines have the following format:
prefix/prefix_length precedence label [# comment ]
The prefix must be an IPv6 prefix in a format consistent with
inet(3SOCKET). The prefix_length is an integer ranging from 0 to 128.
The IPv6 source address selection and destination address ordering
algorithms determine the precedence or label of an address by doing a
longest-prefix-match lookup using the prefixes in this table, much like
next-hop determination for a destination is done by doing a longest-
prefix-match lookup using an IP routing table.
The precedence is a non-negative integer that represents how the desti‐
nation address ordering mechanism will sort addresses returned from
name lookups. In general, addresses with a higher precedence will be in
front of addresses with a lower precedence. Other factors, such as des‐
tinations with undesirable source addresses can, however, override
these precedence values.
The label is a string of at most fifteen characters, not including the
NULL terminator. The label allows particular source address prefixes to
be used with destination prefixes of the same label. Specifically, for
a particular destination address, the IPv6 source address selection
algorithm prefers source addresses whose label is equal that of the
destination.
The label may be followed by an optional comment.
The file must contain a default policy entry, which is an entry with
"::0/0" as its prefix and prefix_length. This is to ensure that all
possible addresses match a policy.
OPTIONS
The ippadrsel utility supports the following options:
-f file Replace the address selection policy table with the
policy specified in the file.
-d Revert the kernel's address selection policy table
back to the default table. Invoking ipaddrsel in
this way only changes the currently running ker‐
nel's policy table, and does not alter the configu‐
ration file /etc/inet/ipaddrsel.conf. To revert the
configuration file back to its default settings,
use ipaddrsel-d, then dump the contents of the ta‐
ble to the configuration file by redirecting the
output of ipaddrsel to /etc/inet/ipaddrsel.conf.
example# ipaddrsel-d
example# ipaddrsel > /etc/inet/ipaddrsel.conf
EXAMPLES
Example 1 The Default Policy in /etc/inet/ipaddrsel.conf
The following example is the default policy that is located in
/etc/inet/ipaddrsel.conf:
# 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
Example 2 Assigning a Lower Precedence to Link-local and Site-local
Addresses
By default, the destination address ordering rules sort addresses of
smaller scope before those of larger scope. For example, if a name
resolves to a global and a site-local address, the site local address
would be ordered before the global address. An administrator can over‐
ride this ordering rule by assigning a lower precedence to addresses of
smaller scope, as the following table demonstrates.
# Prefix Precedence Label
::1/128 50 Loopback
::/0 40 Default
2002::/16 30 6to4
fec0::/10 27 Site-Local
fe80::/10 23 Link-Local
::/96 20 IPv4_Compatible
::ffff:0.0.0.0/96 10 IPv4
Example 3 Assigning Higher Precedence to IPv4 Destinations
By default, IPv6 addresses are ordered in front of IPv4 addresses in
name lookups. ::ffff:0.0.0.0/96 has the lowest precedence in the
default table. In the following example, IPv4 addresses are assigned
higher precedence and are ordered in front of IPv6 destinations:
# Prefix Precedence Label
::1/128 50 Loopback
::/0 40 Default
2002::/16 30 6to4
::/96 20 IPv4_Compatible
::ffff:0.0.0.0/96 60 IPv4
Example 4 Ensuring that a particular source address is only used when
communicating with destinations in a particular network.
The following policy table assigns a label of 5 to a particular source
address on the local system, 2001:1111:1111::1. The table assigns the
same label to a network, 2001:2222:2222::/48. The result of this policy
is that the 2001:1111:1111::1 source address will only be used when
communicating with destinations contained in the 2001:2222:2222::/48
network. For this example, this network is the "ClientNet", which could
represent a particular client's network.
# Prefix Precedence Label
::1/128 50 Loopback
2001:1111:1111::1/128 40 ClientNet
2001:2222:2222::/48 40 ClientNet
::/0 40 Default
2002::/16 30 6to4
::/96 20 IPv4_Compatible
::ffff:0.0.0.0/96 10 IPv4
This example assumes that the local system has one physical interface,
and that all global prefixes are assigned to that physical interface.
EXIT STATUSipaddrsel returns the following exit values:
0 ipaddrsel successfully completed.
>0 An error occurred. If a failure is encountered, the ker‐
nel's current policy table is unchanged.
FILES
/etc/inet/ipaddrsel.conf The file that contains the IPv6
default address selection policy to
be installed at boot time. This
file is loaded before any Internet
services are started.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │SUNWcsu │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Evolving │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOnscd(1M), inet(3SOCKET), getaddrinfo(3SOCKET), ipaddrsel.conf(4),
attributes(5), inet6(7P)NOTES
The ipnodes cache kept by nscd(1M) contains addresses that are ordered
using the destination address ordering algorithm, which is one of the
reasons why ipaddrsel is called before nscd in the boot sequence. If
ipaddrsel is used to change the address selection policy after nscd has
started, you should invalidate the nscd ipnodes cache invalidated by
invoking the following command:
example# /usr/sbin/nscd -i ipnodes
SunOS 5.10 16 Jul 2004 ipaddrsel(1M)
