IPv6 TCP/IP Addressing

The Internet has grown and continues to grow at an exponential rate. Eventually the Internet will run out of network numbers. Therefore, a new IP protocol called IPv6 is replacing IPv4.

IPv6 provides a number of benefits for TCP/IP-based networking connectivi- ty, including

. Large address space: The 128-bit address space for IPv6 potentially provides every device on the Internet with a globally unique address.

. Efficient routing: The IPv6 network packet supports hierarchical routing infrastructures, which enables more efficient routing than IPv4.

. Straightforward configuration: IPv6 can use both DHCP for IPv6 (DHCPv6) and local routers for automatic IP configuration.

. Enhanced security: The IPv6 standard provides better protection against address and port scanning attacks and all IPv6 implementations support IPsec for protection of IPv6 traffic.

IPv4 is based on 32-bit addresses (four 8-bit octets), which allows a little more than 4 billion hosts. IPv6 uses 128 bits for the addresses, which can have up to

3.4 x1038 hosts. Thus, IPv6 can handle all of today’s IP-based machines and

Introduction to TCP/IP

allow for future growth while handling IP addresses for mobile devices such as personal digital assistants (PDAs), cell phones, and similar smart devices.

An IPv6 address is divided into groups of 16 bits, written as four hex digits. Hex digits include 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F. The groups are separated by colons. An example of an address is

FE80:0000:0000:0000:02A0:D2EF:FEA5:E9F5 Similar to IPv4, the IPv6 addresses are split in two parts: bits that identify the

network and bits that define the host address. Different from IPv4, IPv6 has a fixed prefix that contains specific routing and subnet information. The first 64 bits (four groups of four hex digits) define the network address and the second

64 bits define the host address. For the address of FE80:0000:0000:0000: 02A0:D2EF:FEA5:E9F5, FE80:0000:0000:0000 defines the network bits and 02A0:D2EF:FEA5:E9F5 defines the host bits.

While IPv6 addresses are expressed with hexadecimal digits, a 128-bit address still uses 32 hexadecimal digits. Therefore, in some situations, you can abbreviate an IPv6 address. When an IPv6 address has two or more consecutive eight- bit blocks of zeroes, you can replace them with a double colon, as follows:

42cd:0051:0000:0000:c8ba:03f2:003d:b291 This becomes

42cd:0051::c8ba:03f2:003d:b291 You can also remove the leading zeros in any block. Therefore, for our exam-

ple, you have 42cd:51::c8ba:3f2:3d:b291

The IPv6 address types include the following: . Unicast: Used for one-to-one communication between hosts. Each IPv6

host has multiple unicast addresses. The Unicast IPv6 can be further broken down to

. Global Unicast address: Addresses that are equivalent to IPv4

public addresses so they are globally routable and reachable on the IPv6 portion of the Internet. Global Unicast addresses start with a

2 or 3. . Link-Local addresses: Used by hosts when communicating with

neighboring hosts on the same link. They are equivalent to IPv4 APIPA addresses and start with FE8.

CHAPTER 5: Configuring Windows Networking

. Unique local unicast addresses: Equivalent to IPv4 private address spaces and start with FEC0.

. Multicast: Used for one-to-many communication between computers that are defined as using the same multicast address.

. Anycast address: An IPv6 unicast address that is assigned to multiple computers. When IPv6 addresses communicate to an anycast address, only the closest host responds. You typically use this for locating services or the nearest router.

The last 64-bits of an IPv6 address are the interface identifier. This is equivalent to the host ID in an IPv4 address. Each interface in an IPv6 network must have a unique interface identifier. Some network implementations use EIU-64, which derives the last 64-bits based on the MAC address.

Because the interface identifier is unique to each interface, IPv6 uses it rather than media access control (MAC) addresses to identify hosts uniquely. Because the MAC address can partially be used to uniquely identify a computer, some IPv6 implementations generate a unique interface identifier to preserve priva- cy in network communication rather than using the network adapter’s MAC address.

In the next-generation Internet Protocol, IPv6, ARP’s functionality is provid-

ed by the Neighbor Discovery Protocol (NDP). NDP is responsible for . Address autoconfiguration of nodes . Discovery of other nodes on the link . Determining the Link Layer addresses of other nodes . Duplicate address detection . Finding available routers and Domain Name System (DNS) servers . Address prefix discovery . Maintaining reachability information about the paths to other active

neighbor nodes

ExamAlert

If you need to assign a computer directly to the Internet, you should configure the computer with an IPv6 address that is equivalent to a public IPv4 address, which is

a global unicast IPv6 address. These addresses are globally routable and can be reached from the Internet. However, computers running Windows 7 are usually con- nected through your ISP, which is automatically assigned an IPv6 address.

Introduction to TCP/IP

Similar to the loopback address of 127.0.0.1 used for testing, IPv6 uses 0:0:0:0:0:0:0:1. To abbreviate this address, you can write it as ::1.

Because most networks use IPv4, there are several methods that were created to transition from IPv4 to IPv6. Windows 7 and Windows Server 2008 R2 support the following methods:

. IPv4-compatible address: 0:0:0:0:0:0:w.x.y.z or ::w.x.y.z (where w.x.y.z is the dotted decimal representation of a public IPv4 address) is used by IPv6/IPv4 nodes that are communicating using IPv6. The address format consists of 96 bits of zeroes, followed by an IPv4 address in its standard dotted-decimal notation. As a result, an IPv4-compatible address is used as an IPv6 destination. The IPv6 is automatically encapsulated with an IPv6 header and sent to the destination using the IPv4 infrastructure. An example is ::192.168.1.20.

. IPv4-mapped address: The IPv4-mapped IPv6 address has its first 80 bits set to zero, the next 16 set to one, and the last 32 bits represent the IPv4 address. For example, ::FFFF:C000:280 is the mapped IPv6 address for 192.0.2.128. Remember, the 192.0.2.128 is written in decimal format, while the C000:280 is written in hexadecimal format. The IPv4-mapped IPv6 addresses always identify IPv4-only nodes. An example is ::ffff:192.168.1.20.

. 6to4 address: A tunneling technology that enables computers to trans- mit IPv6 packets over an IPv4 network. The 6to4 address is formed by combining the prefix 2002::/16 with the 32 bits of a public IPv4 address, forming a 48-bit prefix. An example using the 192.168.1.20 IPv4 address appears as follows: 2002:C0A8:0114::/16. 6to4 is enabled by default on machines running Windows 7.

IPv6 TCP/IP Addressing