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Cisco CCNP ROUTE 642-902: IPv6 Primer

  • Nov 10, 2010
A key topic on the CCNP ROUTE exam, this article helps you understand how the IPv6 protocol is structured and how the addresses are notated and organized. The use and implementation of IPv6 and its associated protocols is inevitable with the ongoing growth of worldwide connections, and it will be important for all people involved with these networks to have this basic knowledge.
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This article is a primer for those who don’t have much experience with IPv6 and want to learn the basics of how the protocol is structured, how the addresses are notated, and how the addresses are organized for use, and also to review of the technologies that are used with it on modern networks. The use and implementation of IPv6 and its associated protocols is inevitable with the ongoing growth of worldwide connections, and it will be important for all people involved with these networks to have this basic knowledge.

IPv6 and IPv4 Compared

The most obvious starting point is why to implement IPv6 in the first place. As most people who work in the networking field know, the number of IPv4 addresses is limited in the total amount of addresses available. Throughout the last 15 years, this has continued to be a larger issue as the number of people accessing the Internet has grown. Now, the inevitable path towards its successor has been delayed by several different programs and technologies, but it is coming, and it is coming up on the time where networking people should at least be aware of the IPv6 basics.

The IPv6 header is constructed as shown in Figure 1.

Figure 1

As you can see, if you are familiar with the IPv4 header, there are a number of differences between each type. The IPv6 header was designed to be simpler and streamlined compared to IPv4. This simplification allows the protocol to be easier to read, to make decisions on, and to forward. The following table details what the various fields are used for.

Field

Field Description (Version 6)

Version

This field is simply used to notate that this is IP version 6.

Traffic Class

The traffic class field is used in a similar fashion to the ToS field in IPv4, which allows the creation of different traffic classes. These classes can then be used with a QoS technology to prefer specific traffic over other traffic.

Flow Label

This field is used to identify traffic flows. The use of this field is evolving with the technology.

Payload Length

The overall length of the data in the packet.

Next Header

This field works similarly to the IPv4 Protocol field, which identifies how the traffic will be identified. For example, is it TCP or UDP traffic?

Hop Limit

This field works like the IPv4 TTL field; it is used to control the total forwarding hops which are allowed for a specific packet.

Source Address

This is the source IPv6 address.

Destination Address

This is the destination IPv6 address.

Now the IPv6 address is 128 bits long; in comparison, the IPv4 address is only 32 bits long. The amount of addresses that can be assigned using IPv4 is 232 or 4,294,967,296 addresses. Of this number, at the time of this writing it is estimated that there are just fewer than 200 million available. The IPv6 address space allows for 2128 or 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses. This of course would give us the ability to address almost everything in our daily lives.

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