We Provide Specifications Of The Ipv6 Protocol

Chapter 2

Internet Protocol version 6

In this chapter we provide specifications of the IPv6 protocol. It describes all the parameters and features associated with this protocol.

2.1 Header Format

2.2 Addressing

An IPv6 address is of 128 bits represented in 8 hexadecimal blocks, separated by ‘:’. Each block carries 16 bits. Ex. X:X:X:X:X:X:X:X ; 2001:4408:0000:0000:0000:c123:7820:1111. It is case insensitive. A block of zeroes or leading zeroes in the address can be replaced with ‘::’, but only once. Ex. 2001:4408::c123:7820:1111

1 64 128

Global routing prefix Subnet ID Interface ID

Figure 2.1 IPv6 Address Format

An IPv6 address is split into three parts: global routing prefix, subnet ID and interface ID

(refer to Figure 2.1).

The global routing prefix helps in identifying the range of addresses allocated to a site. The subnet ID defines a link within a site. The interface ID identifies an IPv6 interface on a subnet and must be unique within that subnet.

For all addresses, the interface ID has to be exactly 64 bits long. This makes the differentiation between network- & host portion easy since the boundary is always the same. On the contrary, in IPv4, the size of the subnet could vary using the Variable Length Subnet Mask (VLSM) technique. The interface ID is created using Modified EUI-64 Format Interface Identifiers algorithm, which takes the 48 bit long MAC address of the Ethernet card and expands it to the 64 bits needed for the interface ID. This has a disadvantage. An interface will always have the same interface ID independent of what site it resides or what prefix it currently uses and thus node becomes traceable.

IPv6 addresses are of three types:

1. Unicast- it uniquely identifies a singl...

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...le, to resolve the link-layer address via multicast. The solicited-node multicast address has the form of ff02::1:ffxx:xxxx. The all-nodes multicast address is recognised by prefix ff02::1 and is assigned by default to every IPv6 interface. Through this address one can reach all interfaces by only single packet. In case the IPv6 host is a router, it us assigned the all-routers multicast address with prefix ff02::2. The following table summarizes all the above mentioned addresses with example.

Global unicast address (EUI-64) 2001:db8:72ed:1:240:d0ff:fe8d:4546/64

Global unicast address 2001:db8:72ed:1:7d2c:2184:c541:dedf/64

Link-Local unicast address fe80::240:d0ff:fe8d:4546/64 All-Nodes multicast address ff02::1 Solicited-Node multicast (EUI-64) ff02::1:ff8d:4546 Solicited-Node multicast ff02::1:ff41:dedf

Table 2.1 IPv6 Addresses Assigned to an Interface