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Notes of Computer Networks and Security [CT 702]

Introduction to IPV6

IPv6 Advantages

Limitations of IPv4

- Due to address class allocation practices, public IPv4 addresses are becoming scarce. Because of this, it forces deployment of network address translator to share a public IPv4 address among several private addresses. But, NAT adds complexity and also becomes barrier for applications.
- IPv4 works with flat routing infrastructure in which individual address prefixes were assigned and each prefix became a new route in the routing table.
- IPv4 must be configured either manually or through DHCP.
- It do not have built-in security and rely upon Ipsec for security.
- Due to lack of infrastructure, communication with IPv4 mobile node are inefficient.

IPv6 as replacement of IPv4

- IPv6 addresses are 128 bits long, creating a huge amount of address space.
- It uses hierarchical routing infrastructure. It results in relatively few routing entries in the routing table.
- It is automatically configure with the host’s IPv6 address.
- It supports for Ipsec protocol headers is required. IPv6 packets are not required to be protected with Authentication header (AH) or Encapsulating Security Payload (ESP).
- It is capable of supporting mobility more efficiently.

Packet Fomats

- IP header contains many fields used by routers to forward the packet from network to network to a final destination.
- Payload represents information to be delivered to the receiver by the sender.
- The basic packet structure is:
| Header | Payload |

Header Structure

The header structure of IPv4 and IPv6 are shown in given figure:


Header Structure Comparison

- IPv6 header is simpler than IPv4 header.
- IPv6 header size is bigger than that of IPv4.
- The source and destination addresses are 32 bit in IPv4 header while 128 bit in IPv6 header.
- IPv4 header is of variable size with minimum of 20 byte in length. IPv6 header is of fixed size with 40 byte in length.

Transition from IPv4 to IPv6

Dual Stack Router:

- A router can be installed with both IPv4 and IPv6 address configured on its interfaces pointing to the network of relevant IP scheme.
- It is capable of communicating with both types of network.
- It provides a medium for the hosts to access a server without changing their respective IP versions.
- IPv6 is not supported on all of the IPv4 devices.



- Tunneling provides a solution where user data can pass through a non supported IP version.
- Two remote IPv4 networks can communicate via a tunnel where the transit network is on IPv6.
- Two remote IPv6 networks can communicate via a tunnel where the transit network is on IPv4.


NAT Protocol Translation:

- It is the important method of transition to IPv6 by means of a Network Address Translation – Protocol Translation (NAT – PT) enabled device.
- With the help of NAT – PT device, actual translation can take place between IPv4 and IPv6 packets and vice versa.
- When IPv4 host sends a request packet to IPv6 server, NAT – PT device strips down IPv4 packet, removes IPv4 header and adds IPv6 header and passes it through the Internet.
- When a response from IPv6 server comes for the IPv4 host, the router does the reverse action.



- Dual stack allows IPv4 and Ipv6 to coexist in the same devices and networks.
- Tunneling allows transport of IPv6 traffic over the existing IPv4 infrastructure.
- Translation allows IPv6 only nodes to communicate with IPv4 only nodes.



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