Ipv6

Networking IPv6 User Guide for J2SDK/JRE 1.4
This document covers the following topics:
q Overview
q

Supported Operating Systems

q

Special IPv6 Address Types

q

IPv6-Related System Properties

q

Dual-Stack Node

q

Java Application Impact

q

IPv6 Networking Properties

Overview
With the J2SDK/JRE 1.4 release, IPv6 support has been added to Java Networking. Thiswill make J2SE compliant with the
following standards (RFCs):
q RFC2373: IPv6 Addressing Architecture;
q RFC 2553: BasicSocket Interface Extensions for IPv6;
q RFC 2732: Format for Literal IPv6 Addresses in URLs.
Since the J2SDK does not support raw sockets, RFC 2292 (: Advanced Sockets API for IPv6) is not supported in this release.
Other interesting features of IPv6, such as tunneling,autoconfiguration of addresses, mobile IP, etc., are not supported at the
Java API level, as they are handled automatically by the underlying OS or system support.

Supported Operating Systems
The following operating systems are supported in this release:
q Solaris 8 and up
q Linux kernel 2.1.2 and up (Red Hat 6.1 and up)
Notes on Linux
1. It is recommended to use Linux kernel 2.4.0 and higherreleases, as IPv6 support is better in those releases.
2. With Linux, you need to install an IPv6-enabled kernel or rebuild the kernel with IPv6 options enabled. (Up until Kernel
2.4.2, the IPv6 implementation is marked as "experimental.") In addition, you will need to install several network
utilities. For detailed information, refer tohttp://www.bieringer.de/linux/IPv6/IPv6-HOWTO/IPv6-HOWTO.html
Notes on Windows
J2SETM 1.4 does not support IPv6 on Microsoft Windows. Microsoft has released an IPv6 Technology Previous for Windows
2000 but this is a limited seperate stack implementation. A complete dual IPv4/IPv6 stack implementation for Microsoft
Windows is not expected to be released until 2002 or later.

Special IPv6 Address Types
Unspecified address (:: corresponding to0.0.0.0 in IPv4)
This is also called anylocal or wildcard address. If a socket is bound to an IPv6 anylocal address on a dual-stack machine, it
can accept both IPv6 and IPv4 traffic; if it is bound to an IPv4 (IPv4-mapped) anylocal address, it can only accept IPv4 traffic.
We always try to bind to IPv6 anylocal address on a dual-stack machine unless a related system property is set to use IPv4Stack.
When bound to ::, method ServerSocket.accept will accept connections from both IPv6 or IPv4 hosts. The Java
platform API currently has no way to specify to accept connections only from IPv6 hosts.
Applications can enumerate the interfaces using NetworkInterface and bind a ServerSocketChannel to each IPv6
address, and then use a selector from the New I/O API to accept connections fromthese sockets.

Note: The option discussed below is introduced in
Draft-ietf-ipngwg-rfc2553bis-03.txt. It will be supported in the Java 2 platform
when it becomes a standard.
However, there is a new socket option that changes the above behaviour. Draft-ietf-ipngwg-rfc2553bis-03.txt has introduced a
new IP level socket option, IPV6_V6ONLY. This socket option restricts AF_INET6 sockets to IPv6communications only.
Normally, AF_INET6 sockets may be used for both IPv4 and IPv6 communications. Some applications may want to restrict
their use of an AF_INET6 socket to IPv6 communications only. For these applications the IPV6_V6ONLY socket option is
defined. When this option is turned on, the socket can be used to send and receive IPv6 packets only. By default this option is
turned off.Loopback address (::1 corresponding to 127.0.0.1 in IPv4)
Packets with the loopback address must never be sent on a link or forwarded by an IPv6 router. There are two separate
loopback addresses for IPv4 and IPv6 and they are treated as such.
IPv4 and IPv6 addresses are separate address spaces except when it comes to "::".
Compatibility address ::w.x.y.z
This is used for hosts and routers to...