ipaddrsel(1M)						  System Administration Commands					     ipaddrsel(1M)

NAME

       ipaddrsel - 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 selection policy table. The policy table is a longest-matching-prefix
       lookup table that is used for IPv6 source address selection  and  for  destination  address  ordering  when  resolving  names  to  AF_INET6
       addresses. For a description of how the policy table is used for source address selection, see inet6(7P). For a description of how the pol-
       icy 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 long-
       est-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 destination 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
       destinations 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  selec-
       tion 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 pos-
       sible 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 kernel's policy table, and does not alter the configuration file /etc/inet/ipaddrsel.conf. To revert the con-
		  figuration file back to its default settings, use ipaddrsel -d, then dump the contents of the table 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
	 ::/96				     20 IPv4_Compatible
	 ::ffff:0.0.0.0/96		     10 IPv4
	 2002::/16			     30 6to4
	 ::/0				     40 Default

       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
       override 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 Used

       This example ensures that a particular source address is used only 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 inter-
       face.

EXIT STATUS

       ipaddrsel returns the following exit values:

       0     ipaddrsel successfully completed.

       >0    An error occurred. If a failure is encountered, the kernel'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 ALSO

       nscd(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 5.11							    6 Feb 2006							     ipaddrsel(1M)