Task 4; network Layer We want to Look at Link State Routing (LSR). a) Explain th

Question

Task 4; network Layer

We want to Look at Link State Routing (LSR).
a) Explain the principle of LSR.
b)Why can the routes in a network using LSR be temporarily inconsistent?
c) If delay is used as distance metric between neighboring nodes, one must determine one of two measurement points. Either you measure the delay from the time packages enter the sending queue, or you measure the delay from the time they are actually sent out on line. What is the difference between the two methods? What do the methods mean in relation to routing?

Explanation / Answer

The link-state protocol is also called the shortest path first algorithms.
It is a dynamic routing algorithm in which each router shares knowledge of its neighbors with every other router in the network.
The Principles of the link-state protocol is:-
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->The principle of link-state routing is that all the routers within an area maintain an identical copy of the network topology.
From this map, each router performs a series of calculations that determine the best routes.
->This network topology is contained within a link-state database, where each record represents the links to a particular node in the network.
->A router sends its information about its neighbors only to all the routers through flooding.
->Information sharing takes place only whenever there is a change.It makes use of Dijkastra’s Algorithm for making routing tables.
->The link-state protocol is performed by every switching node in the network
That means nodes that are prepared to forward packets in the Internet, these are called routers.
  
->Link-state routing protocols require routers to periodically send routing updates to their neighboring routers in the internetwork.
In addition, link-state routing protocols are quick to converge their routing updates across the network in comparison to distance vector protocols.
  
  
  
->Neighbouring nodes synchronize before starting any relationship,Once synchronized, a node accepts link state advertisements
->Which contain a sequence number, stored with record in the database only messages with new sequence number are accepted
accepted messages are flooded to all neighbours sequence number prevents anomalies (loops or blackholes)
  
->When a link-state router boots, it first needs to discover to which routers it is directly connected.
For this, each router sends a HELLO message every N seconds on all of its interfaces.
This message contains the router’s address.
-> Each router has a unique address. As its neighbouring routers also send HELLO messages,
the router automatically discovers to which neighbours it is connected.

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