It is easy for computers to read the new 128-bit IPv6 addressing. IPv6 just adds more ones and zeros to the source and destination addresses in the packet. For humans, though, the change from a 32-bit address written in dotted-decimal notation to an IPv6 address written as a series of 32 hexadecimal digits can be quite an adjustment. Techniques have been developed to compress the written IPv6 address into a more manageable format.
Compressing IPv6 Addresses
IPv6 addresses are written as a string of hexadecimal values. Every 4 bits is represented by a single hexadecimal digit for a total of 32 hexadecimal values. Table 10-2 shows a fully expanded IPv6 address and two methods of making it more easily readable.
Table 10-2 Compressing an IPv6 Address
| Fully Expanded | 2001:0db8:0000:1111:0000:0000:0000:0200 |
| No leading zeros | 2001:db8:0:1111:0:0:0:200 |
| Compressed | 2001:db8:0:1111::200 |
Two rules help reduce the number of digits needed to represent an IPv6 address.
Rule 1: Omit Leading Zeros
The first rule to help reduce the notation of IPv6 addresses is to omit any leading zeros in any 16-bit section. For example, as shown in Table 10-2:
- 0DB8 can be represented as DB8.
- 0000 can be represented as 0.
- 0200 can be represented as 200.
Rule 2: Omit One “All Zero” Segment
The second rule to help reduce the notation of IPv6 addresses is that a double colon (::) can replace any group of consecutive segments that contain only zeros. The double colon (::) can be used only once within an address; otherwise, there would be more than one possible resulting address.
Activity—IPv6 Address Representation (10.4.6)
Refer to the online course to complete this activity.
Lab—Identify IPv6 Addresses (10.4.7)
In this lab, you will complete the following objectives:
- Part 1: Identify the different types of IPv6 addresses.
- Part 2: Examine a host IPv6 network interface and address.
- Part 3: Practice IPv6 address abbreviation.
Summary (10.5)
The following is a summary of each topic in the chapter:
- Network Boundaries—The router provides a gateway through which hosts on one network can communicate with hosts on other networks. Each host must know the IPv4 address of the router interface connected to the network where the host is attached. This address is known as the default gateway address. Local hosts are referred to as being located on an internal, or inside, network. The network assigned to the Internet side of the wireless router is referred to as the external, or outside, network. The wireless router serves as the boundary between the local internal network and the external Internet.
- Network Address Translation—NAT is used to convert private IP addresses used on an internal network to a public (global) address that can be routed through the Internet. One single public address can be used for many internal hosts.
- IPv4 Issues—An IPv4 address is 32 bits (4 bytes) long, meaning there are approximately 4.3 billion IPv4 addresses, which is not enough anymore. The designers of the IP protocols began to become concerned about running out of IPv4 addresses in the early 1990s. In 1993, the IETF started accepting recommendations for enhancements to the IP protocol to support the need for larger address space and to make assigning IP addresses easier for administrators. It took until 1995 for the first IPv6 specification to be published.
An IPv6 address is 128 bits (16 bytes) long, meaning there are enough possible IPv6 addresses to allocate more than the entire IPv4 Internet address space to each person on the planet. IPv6 addressing will eventually replace IPv4 addressing, although both types of addresses will coexist for the foreseeable future. IPv6 does not require NAT, and autoconfiguration capabilities simplify address administration.
Dual stack allows IPv4 and IPv6 to coexist on the same network segment. Dual stack devices run both IPv4 and IPv6 protocol stacks simultaneously. Tunneling is a method of transporting an IPv6 packet over an IPv4 network. The IPv6 packet is encapsulated inside an IPv4 packet, similar to other types of data. Network Address Translation 64 (NAT64) allows IPv6-enabled devices to communicate with IPv4-enabled devices using a translation technique similar to NAT for IPv4. An IPv6 packet is translated to an IPv4 packet, and an IPv4 packet is translated to an IPv6 packet.
- IPv6 Features—IPv6 addresses have other characteristics that are different from those of IPv4 addresses:
- Address autoconfiguration—SLAAC allows a host to create its own GUA without the need for a DHCP server.
- Link-local address—IPv6 addresses can use the link-local address when communicating with a device on the same network.
The developers of IPv6 also made improvements to IP and related protocols such as ICMPv6, including features related to efficiency, scalability, mobility, and flexibility for future enhancements.
IPv6 addresses are written as a string of hexadecimal values. Every 4 bits is represented by a single hexadecimal digit for a total of 32 hexadecimal values. Because of the size of an IPv6 address, techniques have been developed to compress the written IPv6 address into a more manageable format. Two rules help reduce the number of digits needed to represent an IPv6 address:
- Rule 1: Omit Leading Zeros—The first rule to help reduce the notation of IPv6 addresses is to omit any leading zeros in any 16-bit section.
- Rule 2: Omit One “All Zero” Segment—The second rule to help reduce the notation of IPv6 addresses is that a double colon (::) can replace any group of consecutive segments that contain only zeros. The double colon (::) can be used only once within an address; otherwise, there would be more than one possible resulting address.
