IPv6 (Internet Protocol Version 6)

5. IPv6 Loopback address

Loopback address is a special IP number that is designated for the software loopback interface of a machine. The loopback interface has no hardware associated with it, and it is not physically connected to a network.

The loopback interface allows IT professionals to test IP software without worrying about broken or corrupted drivers or hardware.

IPv6 Loopback address is 0:0:0:0:0:0:0:1

It can also be expressed as ::1

6. IPv6 Reserved Address Space

IPv6 reserves two special addresses. They are 0:0:0:0:0:0:0:0 and 0:0:0:0:0:0:0:1. IPv6 uses 0:0:0:0:0:0:0:0 internal to the protocol implementation, so nodes cannot use it for their own communication purposes. IPv6 uses 0:0:0:0:0:0:0:1 as its Loopback address equivalent to 127.0.0.1 in IPv4

7. IPV6 Header

IPv6 header contains the following things:

1. Version - This field contains the version of the IP used in the packet. It is of 4-bit in IP version 6.

2. Traffic class - This is an 8-bits field determining the packet priority. Priority values subdivide into ranges: traffic where the source provides congestion control and non-congestion control traffic.

3. Flow label - This 20 bits specifies the QoS management. Originally created for giving real-time applications special service, but currently unused.

4. Payload length - This 16 bits determines the payload length in bytes. When cleared to zero, the option is a "Jumbo payload" (hop-by-hop).

5. Next header - This 8-bits field specifies the next encapsulated protocol. The values are compatible with those specified for the IPv4 protocol field.

6. Hop limit - This is an 8-bits field newly introduced in IPv6. It replaces the time to live field of IPv4.

7. Source Address - This 128 bits field determines the logical address of the host that is sending the packet.

8. Destination Address - This 128 bits field determines the logical address of the host that is receiving the packet

8. Differences between IPv4 and IPv6

IPv4	IPv6
Source and destination addresses are 32 bits in length	Source and destination addresses are 128 bits in length
IPsec support is optional	IPsec support is required
Header includes checksum	Header does not include checksum
Header includes options	All optional data are moved to IPv6 extension headers
Broadcast addresses are used to send traffic to all nodes on a subnet.	IPv6 uses a link-local scope all-nodes multicast address
Must be configured either manually or through DHCP	Does not require manual configuration or DHCP
IPv4 header does not identify packet flow for QoS handling by routers.	IPv6 header contains Flow Label field, which identifies packet flow for QoS handling by router.
Both routers and the sending host fragment packets.	Only the sending host fragments packets; routers do not.