(a) The broadcast protocol in Question 1 above is an abstraction of what is used
ID: 658550 • Letter: #
Question
(a) The broadcast protocol in Question 1 above is an abstraction of what is used in link-state
routing. In link-state routing, what information does each node broadcast to all other
nodes? What does each node do with the information collected?
(b) How does link-state routing deal with the problem of wrap-around of timestamps (i.e.
sequence numbers) in link-state advertisements?).
(c) Assume a router dies. How do other nodes learn about this? How will nodes change their
routing tables after they learn the router is dead?
Explanation / Answer
(a)
Link-state routing Algorithm:
The link state algorithm is used to obtain the shortest path first from the links of one node to all other nodes.
Working of the algorithm:
The packet switching technique is used in Link-state routing algorithm.
The packet switches across the network and sends messages periodically. The message also carries the status of the link between two packet switches.
The status of the link between the nodes for packet switches is determined.
The message that contains the status is broadcast to all switches.
The incoming status messages are received by the remaining nodes and they use them in building a network using a graph.
(b)
The sequence number wraparound causes the protocol to stop functioning properly.
When the wrap around occurs two packets with same sequence number and different packets are switching at same time the first acknowledge the second illegitimately and vice versa.
This results in packet loss.
To avoid this, link state routing algorithm carries the linking between the nodes as follows:
The complete set of link-state advertisements (one from each node in the network) are maintained at each node producing the map for the network graph.
The algorithm continuously iterates over the link-state advertisements.
For each link advertisement, a link is created on the map of the network, from the source node that sends the message to all the other nodes that the message indicates as its neighbors.
When the link between the two nodes is not correctly reported by the two nodes then the link is not included in the map.
(c)
When the router does not get update with the shortest path links then the router is said to be dead. In simple words, when the router is non-responsive it is said to be dead.
In link state protocol each node updates their routing tables independently using the status messages.
The nodes maintain their own routing tables and update the shortest path in the new routing table.
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