Question

21. What is the unspecified address in IPv6? And what it is used for? 

22. What are different mechanisms used for IPy4 and IPv6 transitions and migration? 

23. What are various forms of shortened version of this IPv6 address can get represented by? 

4BF5:0000:0000:0000:BASF:039A:000A:2176 

24. How does IPv6 allow a payload size of more than 64K? Which header is used to facilitate this? 

25. What are different types of cost metrics often used in routing algorithm to determine the shortest path? 

26. What is the advantage of hierarchical routing? 

27. What are the significance of the fields "H" and "G" in a host's or router's routing table entry?

Answer 1

21.

An IPv6 address with all 128 bits set to zero is called the unspedified adddress (which correspond to 0.0.0.0 in IPv4). This address should not be assigned to any host and it should only be used as the source address by initializing host before it has learned of its own address. If a host listens for incoming connection on this address, it means that the host and/or its application is listening on all interfaces belong to that host.

The unspecified address (0:0:0:0:0:0:0:0 or ::) is used only to indicate the absence of an address. It is equivalent to the IPv4 unspecified address of 0.0.0.0. The unspecified address is typically used as a source address when a unique address has not yet been determined. The unspecified address is never assigned to an interface or used as a destination address.

In IPv6, the unspecified IPv6 address is 0000:0000:0000:0000:0000:0000:0000:0000/0. This unspecified address is so lengthy and can be further simplified as ::/0.

22. IPv4/IPv6 Transition Mechanisms

The transition between the IPv4 Internet today and the IPv6 Internet of the future will be a long process during both protocols coexists. Figure 1 shows the transition phases. A mechanism for ensuring smooth, stepwise and independent changeover to IPv6 services is required. Such a mechanism must help the seamless coexistence of IPv4 and IPv6 nodes during the transition period. IETF has created the Ngtrans Group to facilitate the smooth transition from IPv4 to IPv6 services. The various transition strategies can be broadly divided into three categories, including dual stack, tunneling and translation mechanisms.

MIGRATION

• IPv6 and IPv4 hosts must interoperate.
• The use of IPv6 hosts and routers must be distributed over the Internet in a simple and progressive way, with a little interdependence.
• Network administrators and end users must think that the migration is easy to understand and implement.
• Possibility of a progressive and nontraumatic transition: IPv4 hosts and routers can be updated to IPv6, one at a time, without requiring other hosts or routers to be updated simultaneously.
• Minimum requirements for updating: The only requirement for updating hosts to IPv6 is the availability of a DNS server to manage IPv6 addresses. No requirements are needed for routers.
• Addressing simplicity: When a router or a host is updated to IPv6, it can also continue to use IPv4 addresses.
• Low initial cost: No preparatory work is necessary to begin the migration to IPv6.
• A structure of IPv6 addresses that allows the derivation of IPv6 addresses from IPv4 addresses.
• The availability of the dual stack on hosts and on routers during the transition—that is, the presence of both IPv4 and IPv6 stacks at the same time.
• A technique to encapsulate IPv6 packets inside IPv4 packets (tunneling) to allow IPv6 packets to traverse clouds not yet updated to IPv6.
• An optional technique that consists of translating IPv6 headers into IPv4 headers and vice versa to allow, in an advanced phase of the migration, IPv4-only nodes to communicate with IPv6-only nodes.

25.

Metrics are cost values used by routers to determine the best path to a destination network. Several factors help dynamic routing protocols decide which is the preferred or shortest path to a particular destination. These factors are known as metrics and algorithms.

Metrics are the network variables used in deciding what path is preferred in terms of these metrics. For some routing protocols these metrics are static and may not be changed. For other routing protocols these values may be assigned by a network administrator. The most common metric values are hop, bandwidth, delay, reliability, load, and cost

26. Advantages of Hierarchical Routing :

• Smaller sizes of routing tables.
• Substantially lesser calculations and updates of routing tables.
• Scalability,It shows the capability of the router when the specific operations are performed on the network.