IPv6 in Depth

Rishabh Sharma
3 min readApr 11, 2022


IPv6 or Internet Protocol version 6 is the latest version of IP. IPv6 is the successor of IPv4 and is mostly based on it. IPv6 is built on IPv4 but it provides some improvements to the addressing system, security and maintenance.

You may like to read basics of networking here.

IPv6 Header

An IP header contains application information and also includes the source and destination address. IPv6 header eliminates the fields that are unneeded or rarely used in IPv4 and adds some fields that provide better support for real time traffic.

IPv6 header structure
  • Version- It is the version of IP.(size- 4bits)
  • Traffic Class-It indicates the priority or the class of IPv6 packet(size-8bits)
  • Flow Label- It indicates that the packet belong to a specific sequence of packet b/w source & destination and requires a special handeling by IPv6 routers. (size-20 bits)
  • Payload Length- Indicates the length of IPv6 Payload.(size-16bits)
  • Next Header- It indicates the type of first extension header or protocol in the upper layer.(size-8bits)
  • Hop Limit- It is maximum number of links over which IPv6 packet can travel before being discarded.(size-8bits)
  • Source Address- It indicates the IPv6 address of the host(origin). (size- 128 bits)
  • Destination Address- It indicates the address of the current destination node. (size-128bits)

IPv6 Addressing

IPv6 uses 128 bits addressing model. It does not support broadcast addresses but uses multicast addresses instead.


  • It consists of 8 groups of 16 bit hexadecimal values separated by colons(:)
Eg 3DFE:0000:0000:0002:0212:F6FG:54DF

We can also omit the leading zeros

It becomes- 3DFE:0:0:2:212:F6FG:54DF

Address Type-

There are 3 type of IPv6 addresses-

Unicast- It identifies only a single interface. When a packet is sent to a unicast address it only goes to specific interface identified by the address.

Unicast (Src- tutorialspoint)

Multicast- Multicast addresses are for group of devices on the same network. When a packet is sent to multicast address , the device broadcasts the packet to all interfaces identified by that address.

Multicast(Src- tutorialspoint)

Anycast- Multiple devices(interfaces) are assigned with same Anycast IP address. When host wishes to communicate with a host equipped with an Anycast IP address , it sends a unicast request.

They are for group of devices in multiple locations sharing one destination IP address.

Anycast(Src- tutorialspoint)