e 16 bit value of each X is presented without leading zeros. Furthermore, when the address has 32 or more consecutive zero bits, the zero bit sequence can be abbreviated with syntax The : can be used only once in an address. If an address has multiple series of zeros, the : must be used where it makes the most difference. Here is an example of compressing zeros away from an IPv6 address: 2001:0db8:0000:0000:0000:0000:0000:000a can be presented in much more readable form as 2001 : db8 : a A special textual addressing format has also been defined for IPv6 addresses that are carrying IPv4 address in the lowest 32 bits. The address format for such addresses is d. d. d. d, where ds represent an IPv4 address [15]. An example of such embedded address is: 64: ff9b: : 192.0.2.1 [17]. When an IPv6 address needs to be shown with a port number, square brackets, [ and ], should be used to make the address unambiguous. Without brackets it might be difficult to determine whether the last digit is a port number or part of an IPv6 address, as illustrated here: 2001 db8 : a 80. A correct example, using brackets, makes the distinction clear: [2001 :db8::a] : 80. Many applications, such as web browsers, expect IPv6 addresses to be put in square brackets. As in IPv4, SO in IPv6, the address is divided into the network prefix and the host part. In IPv6, the host part is called the Interface IDentifier (IID). The IID for the unicast addresses is defined to be 64 bits long [15]. The IID must at least be unique in the scope of the link where the interface (and hence, the node) is located. However, the IID can also be unique in a larger scope as well. The network prefix length is noted in the same way in IPv6 as previously described for IPv4. For instance, 2001 41d0: 7827 : 64 means that the network prefix is 64 bits long, and in 2001:41d0:1::/48 the prefix length is 48 bits. Consequently, the length of the IID to 64 bits also constrains the network prefix length at a maximum of 64 bits. Hence, allocating at least a network prefix of /64 