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== Description of IPv6 Packet Header ==
== Description of IPv6 Packet Header ==
Revision as of 18:45, 13 June 2011
Many of the finest developers and engineering minds have been working on IPv6 since the early 1990s. Hundreds of RFCs have been written and have detailed some major areas, including expanded addressing, simplified header format, flow labeling, authentication, and privacy. Expanded addressing moves us from 32-bit address to a 128-bit addressing method. It also provides newer unicast and addressing methods, injects hexadecimal into the IP address, and moves from using "." to using ":" as delimiters.
Description of IPv6 Packet Header
The characters A through F represent the decimal values of 10 through 15, as illustrated in Figure: Hex Characters A Through F Represent the Numbers 10 Through 15.
Figure: Hex Characters A Through F Represent the Numbers 10 Through 15
Counting in hex goes as follows: 0 1 2 3 4 5 6 7 8 9 A B C D E F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 and up, as far as you want to go.
Let's look at an example of IPv6 address. The address is an eight-part hex address separated by colons (:). Each part n can equal a 16-bit number and is eight parts long, providing a 128-bit address length (16 * 8 = 128),
Addresses are n:n:n:n:n:n:n:n n = 4 digit hexadecimal integer, 16 * 8 = 128 address.
1080:0:0:0:8:800:200C:417A Unicast address
FF01:0:0:0:0:0:0:101 Multicast address
Included in IPv6 are a number of methods:
Note that there is no explicit notion of "broadcast" in IPv6.
Unicast is a communication between a single host and a single receiver. Packets sent to a unicast address are delivered to the interface identified by that address, as seen in Figure: Unicast Sends Packets to a Specified Interface.
Figure: Unicast Sends Packets to a Specified Interface
Multicast is communication between a single host and multiple receivers. Packets are sent to all interfaces identified by that address, as seen in Figure: Multicast Sends Packets to a Subnet, and Defined Devices Listen for Multicast Packets.
Figure: Multicast Sends Packets to a Subnet, and Defined Devices Listen for Multicast Packets
Packets sent to an anycast address or list of addresses are delivered to the nearest interface identified by that address. Anycast is a communication between a single sender and a list of addresses, as shown in Figure: Anycast Sends Packets to Specified Interface List and Can Contain End Nodes and Routers.
Figure: Anycast Sends Packets to Specified Interface List and Can Contain End Nodes and Routers
Some of the benefits of IPv6 seem obvious: greater addressing space, built-in QoS, and better routing performance and services. However, a number of barriers must be overcome before the implementation of IPv6. The biggest question for most of us will be what the business need is for moving from current IPv4 to IPv6. The killer app has not appeared yet, but it may be closer than we think. The second consideration is the cost-it may not have much to do with hardware replacement cost. All the larger routers have upgradable OSs IOS; the only necessity is the commitment to upgrading IOS. More likely to do with training and support of minor IP devices such as printers and network faxes, they will support the new address space. IPv6 has schemes to support old and new, however, so this may not even be a barrier. The last issue to consider is training: This will need to happen sooner or later because we all need to start thinking about 128-bit addressing based on MAC addresses in HEX. This involves all new ways of addressing and will be an uncomfortable change for many people.
This conclusion may seem negative, but the greater good will overpower all the up-front issues. The issue is not whether you will have to move to IPv6, but when! We all need IPv6; the increased address space is needed for the growth of IP appliances that we are starting to hear about weekly. IP-ready cars are already shipping today. This requires mobility, which is addressed in IPv6.
Of course, a number of very important features have not been discussed in this section, including QoS, mobile IP, autoconfiguration, and security. All these areas are extremely important, and until IPv6 is finished, you should keep referring to the IETF Web site for the most current information. Several new books on IPv6 also are starting to show up on bookstore shelves and should provide the deeper technical detail on address headers and full packet details.
Q - What is the main reason for IPv6 being developed?
A - The main issue surrounding IPv6 is addressing, or the lack of addressing. Many people believe that we are nearly out of the four billion addresses available in IPv4. IPv6 could be the solution to many problems, but IPv6 is still not fully developed and is not yet a standard.
Q - How many bits does the new expanded addressing provide?
A - The expanded addressing moves us from 32-bit address to a 128-bit addressing method.
Q - What other benefits does expanded addressing provide?
A - It provides newer unicast and addressing methods. Expanded addressing also injects hexadecimal into the IP address and moves from using . to using : as delimiters.
Q - What are the new addressing methods included in IPv6?
A - Unicast, multicast, and anycast.
Q - What is unicast?
A - Unicast is a communication between a single host and a single receiver.
Q - What is multicast?
A - Multicast is communication between a single host and multiple receivers.
Q - What is anycast?
A - Anycast is a communication between a single sender and a list of addresses.