IPv6 is the next generation of IP, created to overcome the limitations of IPv4. Although IPv4 has served the Internet well, IPv4 addresses were not allocated efficientlya global shortage of addresses exists, especially in the developing world. The use of private IPv4 addresses and Network Address Translation (NAT) (explained in Chapter 3) has meant that we have been able to cope so far. However, as more people become connected to the Internet with more devices, the ever-increasing need for IP addresses isn't about to disappear. IPv4 and IPv6 have some similarities and some differences. To compare them, we start with the IPv6 packet header, as illustrated in Figure 10-3. Figure 10-3. IPv6 Header Includes 128-Bit Source and Destination Addresses
One noticeable difference between the two versions of the Internet Protocol is the size of the address: IPv6 addresses are 128 bits long, four times larger than IPv4 addresses. Those network administrators who struggled with calculating IPv4 subnet masks might wonder how they will cope with 128-bit IPv6 addresses. However, there is good newsthese 128-bit addresses don't have to be typed into devices; rather, IPv6 devices can automatically configure their own addresses (with minimal typing on your part). IPv6 devices can even have multiple addresses per interface. Other fields of note in the IPv6 header are as follows:
Rather than using dotted decimal format, IPv6 addresses are written as hex numbers with colons between each set of four hex digits (which is 16 bits); we like to call this the "coloned hex" format. An example address is as follows: 2035:0001:2BC5:0000:0000:087C:0000:000A Fortunately, you can shorten the written form of IPv6 addresses. Leading 0s within each set of four hex digits can be omitted, and a pair of colons can be used, once within an address, to represent any number of successive 0s. For example, the previous address can be shortened to the following: 2035:1:2BC5::87C:0:A Similar to how IPv4 subnet masks can be written as a prefix (for example, /24), IPv6 uses prefixes to indicate the number of bits of network or subnet. The following are the three main types of IPv6 addresses:
Broadcast addresses do not exist in IPv6. There are three main types of unicast addresses,[5] as follows:
The IPv6 stateless autoconfiguration process allows IPv6 devices to be automatically configured and renumbered. Routers send out advertisements that include the prefix (/64) to be used on the network. The device then automatically concatenates its MAC address, in EUI-64 format, with this prefix to create its own address. A few other types of unicast addresses exist; they are used for communicating between IPv4 and IPv6 devices or transporting IPv6 packets over an IPv4 network. These addresses would be used when migrating from IPv4 to IPv6. Note Further information on IPv6 can be found at http://www.cisco.com/go/ipv6. |