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Chapter 4: Problem 32

Consider the count-to-infinity problem in the distance vector routing. Will the count-to-infinity problem occur if we decrease the cost of a link? Why? How about if we connect two nodes which do not have a link?

Short Answer

Expert verified
Count-to-infinity does not occur with link cost decreases or adding new links.

Step by step solution

01

Understanding the Problem

The count-to-infinity problem occurs in distance vector routing when there is a network change such as a link failure, and routers continuously update their distances based on incorrect information, indefinitely increasing the hop count before converging.
02

Analyzing Link Cost Decrease

When the cost of a link is decreased, routers immediately recognize the improvement in their routing tables. This scenario does not lead to the count-to-infinity problem as the updates provide quicker and better routing paths, which are easily accepted by routers.
03

Evaluating Connection of Two Nodes

Connecting two nodes that were not previously linked introduces a new path with a finite and typically more favorable cost. This addition is recognized quickly in the network, thus avoiding the count-to-infinity problem, which specifically arises from distant and incorrect updates, not new links.
04

Conclusion

The count-to-infinity problem does not occur when decreasing the cost of a link or connecting two previously unlinked nodes because updates related to better or new paths do not cause infinite loops. Instead, they help the network converge faster.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Count-to-Infinity
The count-to-infinity problem is a well-known issue in distance vector routing protocols. It arises when there is a failure or significant change in the network, such as a link going down. When this happens, routers may errantly escalate their hop count indefinitely, as they keep sharing incorrect distance information with their neighbors. This looping issue occurs because routers periodically exchange routing tables and update their entries based on the knowledge they acquire, which, if incorrect, leads to ever-increasing hop counts that can get stuck at a high number (often the infinity threshold).
Link Cost Change
In the context of distance vector routing, altering the cost of a link can have significant implications on routing dynamics. When a link cost is decreased, routers detect this improvement in their routing tables and quickly adjust to take advantage of the more efficient path. Unlike situations that trigger the count-to-infinity problem, a decreased link cost is a positive change that allows routers to update their routes without getting stuck in a loop. This leads to better and quicker path selections, aiding in effective data transmission.
Network Convergence
Network convergence refers to the state in which all routers within a network have consistent and accurate routing tables following a change, such as a new link or a change in link cost. Fast convergence is crucial for optimal performance and is positively influenced by beneficial updates like cost decreases or new connections. As routers share updated information with each other, they swiftly align on the most efficient routes, minimizing delay and enhancing the network鈥檚 reliability. Efficient convergence ensures that data packets can traverse the network with minimal hassle or interruption.
Routing Tables
Routing tables play a crucial role in distance vector routing by storing information that routers use to determine the next hop on the path to a destination network. Each router maintains its own table, continually updating it based on information received from its neighbors. These tables include metrics like hop count and path cost, which inform decision-making in routing packets. Updates due to changes such as link cost decreases or newly connected nodes are reflected in these tables, reinforcing accurate routing decisions and promoting network efficiency. Properly managed routing tables are essential to avoid pitfalls like the count-to-infinity problem.

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Most popular questions from this chapter

Consider a datagram network using 8-bit host addresses. Suppose a router uses longest prefix matching and has the following forwarding table: \begin{tabular}{cc} \hline Prefix Match & Interface \\ \hline 00 & 0 \\ 010 & 1 \\ 011 & 2 \\ 10 & 2 \\ 11 & 3 \\ \hline \end{tabular} For each of the four interfaces, give the associated range of destination host addresses and the number of addresses in the range.

Describe how packet loss can occur at input ports. Describe how packet loss at input ports can be eliminated (without using infinite buffers).

Consider a virtual-circuit network. Suppose the VC number is an 8-bit field. a. What is the maximum number of virtual circuits that can be carried over a link? b. Suppose a central node determines paths and VC numbers at connection setup. Suppose the same VC number is used on each link along the VC's path. Describe how the central node might determine the VC number at connection setup. Is it possible that there are fewer VCs in progress than the maximum as determined in part (a) yet there is no common free VC number? c. Suppose that different VC numbers are permitted in each link along a VC's path. During connection setup, after an end-to-end path is determined, describe how the links can choose their VC numbers and configure their forwarding tables in a decentralized manner, without reliance on a central node.

A bare-bones forwarding table in a VC network has four columns. What is the meaning of the values in each of these columns? A bare-bones forwarding table in a datagram network has two columns. What is the meaning of the values in each of these columns?

Suppose there are three routers between a source host and a destination host. Ignoring fragmentation, an IP datagram sent from the source host to the destination host will travel over how many interfaces? How many forwarding tables will be indexed to move the datagram from the source to the destination?
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