IPv6 : Java Glossary

IPv6

The successor protocol to IP. Using IPv6 in Java is easy; it is transparent and automatic. Unlike in many other languages, no porting is necessary. In fact, there is no need to even recompile the source files. The new protocol has addresses four times bigger 128 bits (16 bytes) verses the 32 bits (4 bytes) in the current IP version 4.

Note that IPv6 addresses are 128 bits, 16 bytes, 4 times longer than IPv4 addresses. You’d think 64 bits, allowing 18,744,073,709,551,616 addresses, or 30,77,457 addresses per person would have sufficed. However, to avoid another transition for a very long time, they went for 128 bits. This will allow simpler routing, since bands can be assigned for various regions that won’t soon fill up, and require juggling to shift slots from other regions.

The Java class for dealing with these is called java.net.Inet6Address, though java.net.InetAddress will work too. The new headers, surprisingly, have fewer fields than before, and are fixed length 40 bytes to streamline processing. New features include:

128-bit from and 128-bit to address in the header. When presented to humans, these 16-byte IPs are written in hex in 8 groups of 4 hex digits like this 1080:0:0:0:8:800:200C:41FA. Lead zeros on a group may be left off.
Plug & Play. You can get a universally unique address from the 48-bit MAC burned into your Ethernet card. This can be used as the low order 48 bits of your IP address.
Support for packet priority and "flows". Flows are services like live audio or video broadcasts that require special packet handling.
Jumbograms. You can now have packets bigger than 64K.
Routing structure in the address.
Dynamically assigned IPs are standard. Microsoft has a proprietary DHCP scheme for the current IP protocol.

IPv6 Packet Header
Field	Size in bits	Purpose
version	4	6 for IP version 64. This allows IPv4 and IPv6 packets to be mixed.
payload length	16	total size of data payload measured in 8-bit chunks (aka bytes or octets). The means the maximum size of a packet including data is 64K. This means the payload of data is at most 65,496 bytes.
hop limit	8	how many more hops this packet has to live before being discarded as lost or hopelessly late. On each leg of this packet’s journey, this field gets decremented by 1.
source address	128	Who sent the packet. When it finally arrives at its destination the receiver will know who it was from.
destination address	128	Where the packet is going. On each leg of its journey the routing computer uses this to get the packet a little closer to its final destination.
other stuff	36	Miscellaneous fields.

Everything is in big endian byte order.

Java 1.4.1+ handles the new IPs with java.net.InetAddress and java.net.Inet6Address.

Learning More

Sun’s JDK Technote Guide on IPv6 : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 on your local Windows J: drive.

Sun’s Javadoc on InetAddress class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s Javadoc on Inet4Address class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s Javadoc on Inet6Address class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

datagram
DHCP
IP
Neworking Properties
TCP/IP
UDP

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