IPv6 Address Format

IPv6 Address Format

IPv4 used a dotted decimal structure for its addressing. It comprised of 4 octets which can be represented as binary bits or in decimal with values of 0 through 255.

The IPv6 address is 128 bit thus the format is also longer than IPv4.  It has 4 hexadecimal addresses in sets of eight. That means each set has 16 bits. IPv6 addresses use colon (:) as the separator whereas IPv4 used the dot (.).

IPv6 address would like xxxx.xxxx.xxxx.xxxx.xxxx.xxxx.xxxx.xxxx where the x represents some hexadecimal value. This IPv6 notation is also known as the string notation.

As alphabets (A-F) are used in the IPv6 address, they can either small or in capital.

As in IPv4, if we had all bits as 0, then we wrote that as a single 0. Similar can be done for the IPv6 addresses. Example, if the IPv6 address is 0014 it can also be written as only 14.

Type of IPv6 addresses

There are three main types of IP addresses in IPv6, namely:

1.  Anycast
2. Unicast

  •      Global Unicast
  •      Unique Local
  •      Link-Local

3. Multicast

1. ANYCAST: This type of addressing is similar to Multicast. It is a hybrid of a Unicast and a Multicast.  In a Unicast the packet is destined for a single destination. For multicast we see one packet want to reach multiple members in a group or all members in a multicast group.

It is similar to multicast, as multiple interfaces are identified but the packet is sent only to the first interface that is found.

2. UNICAST: The Unicast IP address in IPv6 has some sub types like :

a)      Global Unicast

b)     Link Local

c)      Site Local

d)     Unique local

e)      Special Addresses

f)       Transition Address

Among these the below three are more popular:

a)      Global Unicast: This is like the public IP in IPv4 and this IP address is routable. It starts with 2000::/3( having the first three bits as 001)

b)     Unique Local: This is like the Private Addresses in RFC 1918. This address begins with FC000::/7. These Unique Local addresses are not routable and these address starts with either FC or FD in the initial 2 numbers.

c)      Link Local: This is the default IPv6 address that is automatically configured on an enabled interface in IPv6. These addresses are not routable and begins with FE80::/10. The Link local addresses are not forwarded by the routers. This is somewhat similar to the APIPA addressing.

3. MULTICAST: As the name suggests this is the Class D equivalent of IPv4 address which is used for multicast. In IPv6 the multicast address starts with FF e.g. ( FF00::/8)


-> Global Address: Value of 2000::/3 : Used on Internet or the Public network.


-> Private Address: Value of FE80::/10: These IPs are used by devices that do not need to access Internet, similar to Private IPs of IPv4 ( RFC 1918). FE will be the first two digits and the third can be from 8 through F.


-> Loopback Address:  “::1” : To test the local interface, similar to what the IP address would do in an IPv4 network. It can be written as either 0:0:0:0:0:0:0:1 or ::1


-> Unspecified Address: It is represented by ::, similar to a of an IPv4 address. Basically 0:0:0:0:0:0:0:0 can be written as “::”( double colon).

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