Computer Networks Control Plane Quiz
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Questions and Answers

What is the primary function of the control plane in computer networks?

  • To ensure data encryption during transmission
  • To monitor the traffic load on the network
  • To control the routing of datagrams and configuration of network services (correct)
  • To manage the physical hardware of the routers

Which routing protocol is associated with per-router control in the network?

  • BGP (correct)
  • NETCONF
  • SDN
  • ICMP

In the context of routing algorithms, what does a graph represent?

  • The sequence of data transmission events
  • The layout of computer hardware in a network
  • The operational protocols used in the network
  • The set of routers and their physical connections (correct)

What is a 'good' path in routing algorithms typically defined as?

<p>The path with the least cost (A)</p> Signup and view all the answers

Which approach utilizes a logically centralized controller for managing router forwarding tables?

<p>Software Defined Networking (SDN) (A)</p> Signup and view all the answers

Which of the following protocols is NOT associated with routing algorithms?

<p>NETCONF (B)</p> Signup and view all the answers

How does the control plane interact with routers in an SDN architecture?

<p>Uses a control agent to distribute instructions (A)</p> Signup and view all the answers

What is a significant drawback of the Distance Vector (DV) algorithm during convergence?

<p>It can create routing loops while converging. (B)</p> Signup and view all the answers

How do Link State (LS) algorithms provide robustness in network routing?

<p>By separating route calculations among routers to contain miscalculations. (C)</p> Signup and view all the answers

What administrative structure do routers form to address scalability and administrative control in the Internet?

<p>Autonomous Systems (ASs). (C)</p> Signup and view all the answers

Which statement is true about the Open Shortest Path First (OSPF) protocol?

<p>OSPF employs flooding of link-state information combined with Dijkstra’s algorithm. (C)</p> Signup and view all the answers

What happens when a router fails or misbehaves in a Distance Vector (DV) algorithm environment?

<p>The problem can quickly spread across the network. (C)</p> Signup and view all the answers

What condition determines that the cost of an edge (𝑥, 𝑦) is set to infinity?

<p>If (𝑥, 𝑦) does not belong to the edge set 𝐸. (C)</p> Signup and view all the answers

Which of the following best defines a neighbor node in a graph?

<p>A node connected through an edge with a finite cost. (B)</p> Signup and view all the answers

In which logical condition is the least-cost path identical to the shortest path?

<p>When all edges have the same cost. (D)</p> Signup and view all the answers

What is a key characteristic of centralized routing algorithms?

<p>They rely on full and complete knowledge of the network. (D)</p> Signup and view all the answers

How do static routing algorithms typically operate?

<p>They change only when manually reconfigured. (C)</p> Signup and view all the answers

Which of the following is a potential drawback of dynamic routing algorithms?

<p>They are more susceptible to routing loops and oscillation. (C)</p> Signup and view all the answers

What distinguishes load-sensitive routing algorithms from load-insensitive algorithms?

<p>Load-sensitive algorithms adapt based on traffic variations. (D)</p> Signup and view all the answers

What is a primary characteristic of distance-vector (DV) algorithms?

<p>They disseminate routing information based on neighboring routers. (C)</p> Signup and view all the answers

Which of these scenarios exemplifies dynamic routing behavior?

<p>Changing routes based on daily traffic analysis. (C)</p> Signup and view all the answers

What does a node’s distance vector include?

<p>Its own distance vector and those of its neighbors. (B)</p> Signup and view all the answers

When the link cost from node y to node x changes from 4 to 1, what must y do first?

<p>Inform its neighbors of the updated distance vector. (A)</p> Signup and view all the answers

What occurs at time t1 when z receives the distance vector update from node y?

<p>Z uses the update to compute a new least cost to node x. (A)</p> Signup and view all the answers

What issue arises when the link cost between nodes x and y increases to 60?

<p>Routing loops may occur. (A)</p> Signup and view all the answers

How does poisoned reverse help prevent routing loops?

<p>It signals nodes that the distance to a route is infinite if it's through a certain node. (A)</p> Signup and view all the answers

What limitation does poisoned reverse have?

<p>It is ineffective with loops involving three or more nodes. (D)</p> Signup and view all the answers

What aspect distinguishes link state from distance vector routing?

<p>Link state requires a complete knowledge of the network topology. (A)</p> Signup and view all the answers

What should a node do after calculating its new minimum cost path to a destination?

<p>Update its distance vector and inform its neighbors. (A)</p> Signup and view all the answers

After detecting a change in link cost, at what point does the algorithm reach a quiescent state?

<p>Once no node has changes to report anymore. (B)</p> Signup and view all the answers

What characteristic of the Distance-Vector Routing Algorithm allows nodes to update their information independently?

<p>Asynchronous operation (D)</p> Signup and view all the answers

In the Bellman-Ford equation, what does $d_x(y)$ represent?

<p>Cost of the least-cost path from node x to node y (D)</p> Signup and view all the answers

What is the primary purpose of the Bellman-Ford equation in the Distance-Vector algorithm?

<p>To define how nodes communicate (A)</p> Signup and view all the answers

When does node x update its distance vector in the Distance-Vector Algorithm?

<p>When a cost change is detected or an update is received (B)</p> Signup and view all the answers

In the distance vector example provided, what would be the calculated distance $d_u(z)$ from node u to node z?

<p>$4$ (A)</p> Signup and view all the answers

Which of the following statements about the Distance-Vector algorithm is false?

<p>All nodes must synchronize their updates. (B)</p> Signup and view all the answers

What does the variable $c(x, v)$ represent in the context of the Distance-Vector algorithm?

<p>The cost of the link between node x and its neighbor v (A)</p> Signup and view all the answers

Which of the following best describes the distance vector maintained by a node?

<p>It maintains estimates of costs to all nodes in the network. (C)</p> Signup and view all the answers

In the context of distance vector updates, what does $v^*(y)$ represent?

<p>The next-hop router along the shortest path to destination y (A)</p> Signup and view all the answers

Which statement illustrates a property of the Distance-Vector algorithm?

<p>It can lead to routing loops in some scenarios. (A)</p> Signup and view all the answers

Flashcards

What is the control plane's role in a network?

The control plane manages how data is routed from source to destination and configures network-layer components.

How do routers decide on data paths?

Each router runs routing algorithms to determine good paths for data, usually the least cost.

What is OSPF and where is it used?

OSPF is a routing protocol used within an autonomous system (AS) to exchange routing information between routers.

What is BGP and how does it connect networks?

BGP is used for routing between different autonomous systems (ISPs). It exchanges routing information between them.

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How does SDN manage routing?

A centralized controller computes and distributes forwarding tables to routers, enabling a more flexible and programmable approach to routing.

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What is the purpose of ICMP?

ICMP messages are used to send error messages and diagnostics information across the network.

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What tools are used for network management?

SNMP and NETCONF/YANG are protocols used to manage devices and network configurations.

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Edge Cost

The cost of an edge represents its physical length, link speed, or monetary cost. It is denoted as 𝒄(𝒙, 𝒚) where (𝑥, 𝑦) is the edge.

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Neighbor Node

A node is considered a neighbor of another node if there's a direct connection between them, represented by an edge in the network graph.

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Network Path

A path in a network is a sequence of connected nodes, where each pair of consecutive nodes represents an edge.

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Path Cost

The cost of a path is the sum of the costs of all the edges along that path.

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Least-Cost Path

The least-cost path problem aims to find the most efficient route between a source and destination, minimizing the overall cost of the path.

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Centralized Routing

Centralized routing algorithms calculate the least-cost path using complete knowledge about the network, including the cost of each link.

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Decentralized Routing

Decentralized routing algorithms calculate the least-cost path iteratively using information distributed among routers.

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Static vs. Dynamic Routing

Static routing algorithms change routes very slowly, usually manually, while dynamic routing algorithms adapt automatically to network changes like traffic loads or topology shifts.

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Load-Sensitive vs. Load-Insensitive

Routing algorithms can be classified as load-sensitive or load-insensitive, based on whether they account for network congestion when choosing routes.

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What is Distance Vector (DV) Routing?

DV algorithm is a distance-vector routing protocol where each router maintains a table of distances to all other routers in the network.

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What are the challenges with DV routing?

DV algorithm can encounter convergence issues, leading to routing loops and slow convergence. This means the paths taken by data might not be the most efficient.

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What is Link State Routing?

Link State (LS) protocols are used for routing within an autonomous system (AS). They build a comprehensive map of the network and calculate the shortest paths between routers.

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What is an Autonomous System (AS) in networking?

An Autonomous System (AS) is a collection of routers under a single administrative control, such as a company or ISP, ensuring smooth operation.

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What is OSPF and how does it work?

OSPF (Open Shortest Path First) is a widely-used link-state routing protocol within ASs. It helps routers efficiently determine the best routes to send data within an AS.

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Distance-Vector (DV) Algorithm

An iterative, asynchronous, and distributed routing algorithm where each node exchanges routing information with its neighbors, refining its understanding of the network topology until no more information needs to be exchanged.

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Bellman-Ford Equation

This equation helps determine the cost of the least-cost path from a node x to another node y by considering the cost of each direct connection from x to its neighbors and the minimum cost paths to y from those neighbors.

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Distance Vector

A representation of estimated costs from a node to all other nodes in the network.

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c(x, v)

The cost of traveling from node x to its neighbor v, representing the link between them.

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Dx(y)

The cost of the least-cost path from node x to node y, as estimated by node x.

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Dx

The vector of cost estimates from node x to all other nodes in the network.

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Dv

The distance vector received by node x from its neighbor v.

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Distance Vector Updates

The process of updating a node's distance vector based on new information from its neighbors or changes in link costs. This involves recalculating the least-cost paths to all destinations.

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v*(y)

The next-hop router along the shortest path from node x to destination y, as determined by node x.

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Forwarding Table

The table used by a node to decide the next hop router for a destination. It is updated during the distance vector updates.

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What is a distance vector in a network?

Each node maintains a table with its own distance vector and those of its neighbors. The table updates based on the shortest paths to reach other nodes, considering costs of links.

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How are distances calculated in a distance vector routing protocol?

At each node, the distance to a destination is calculated by adding the link cost to the neighbor's distance to the destination, then taking the minimum among all available routes. This ensures the shortest path is chosen.

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How does a distance vector routing protocol handle link cost changes?

When a link cost changes, the affected node updates its distance vector and informs its neighbors. These neighbors then update their tables, triggering a chain reaction until the network reaches a stable state where the shortest paths are determined again.

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What is the 'count-to-infinity' problem in distance vector routing?

The count-to-infinity problem occurs when a link cost drastically increases, causing a routing loop where nodes keep sending updates, thinking the path is shrinking, leading to inefficient routing and network instability.

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What is 'poisoned reverse' in distance vector routing?

Poisoned reverse is a technique used to prevent routing loops by advertising infinity as the cost to a destination node if the route goes through that node. This helps break the loop by making the path seem unreachable.

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Does poisoned reverse completely solve the count-to-infinity problem?

While poisoned reverse solves some loop problems, it doesn't address loops involving more than two nodes. More complex scenarios require other solutions.

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What is the message complexity of link-state routing?

Link-state routing protocols require each node to know the cost of all links in the network. This allows for a more accurate and efficient routing process, as all nodes have access to the full network topology.

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What is the message complexity of distance vector routing?

Distance vector routing protocols rely on nodes sharing information about their distances to destinations with their neighbors. This can lead to more message overhead, especially in large networks.

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Compare the robustness of link-state and distance vector routing?

Link-state routing algorithms are more robust to link cost changes compared to distance vector routing, as they react to changes globally, leading to more efficient path adjustments.

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Compare the complexity of implementing link-state and distance vector routing?

Distance vector routing is typically simpler to implement and manage compared to link-state routing, at the cost of potential performance issues and vulnerability to the count-to-infinity problem.

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Study Notes

Computer Networks: Network Layer - Control Plane

  • The control plane manages the network-wide logic for routing datagrams and configuring network components.
  • It dictates how a datagram travels from source to destination host and manages network-layer services.

Control Plane Approaches

  • Per-router control: Individual routing algorithms run on each router (e.g., OSPF, BGP).
  • Logically centralized control (SDN): A central controller computes and distributes forwarding tables to routers. A control agent (CA) interacts with the controller in each router.

Routing Algorithms

  • The goal is to find the "best" routes (paths) between senders and receivers (routers).
  • The "best" path often involves minimum cost (e.g., shortest distance, least delay).
  • A graph representation models network problems. Nodes represent routers, and edges represent links or connections between routers.

Routing Algorithm Notation

  • An edge has a cost (e.g., length, speed, monetary cost) associated with it.
  • Cost of a path is the sum of the costs of its edges (c(x1, x2) + c(x2, x3) + ...).
  • Least-cost path between source and destination is the one with the minimum total cost.

Routing Algorithm Classification

  • Centralized (Link-State): Uses global network knowledge to compute the least-cost path. The algorithm must be aware of the cost of each link.
  • Decentralized (Distance-Vector) : Each router iteratively calculates the best path based on information from its neighbors. Calculations proceed until no more information exchange occurs. This method is asynchronous, where routers don't operate in lockstep.
  • Each node broadcasts link-state packets containing details about its connected links and costs.
  • All nodes have a complete network view.
  • Dijkstra's algorithm calculates the least-cost path from one node (source) to all other nodes.
  • Worst-case complexity is O(n²), where n is the number of nodes.

Distance-Vector (DV) Algorithm

  • Each node shares its cost estimates (distance vectors) with its directly connected neighbors.
  • Neighbors update their distance vectors based on this information.
  • The process continues until no more updates are exchanged between neighbors (quiescent state).
  • The algorithm is asynchronous (routers don't need to operate in lockstep).

Bellman-Ford Equation

  • Bellman-Ford equation establishes the cost of the least-cost path from a node to another node, calculated based on minimum cost among neighboring nodes.

OSPF (Open Shortest Path First)

  • An intra-AS routing protocol (within an autonomous system).
  • Uses link-state information and Dijkstra's algorithm.
  • Routers exchange information on link states, calculating the least-cost path.
  • Admins can configure link costs for routing efficiency (e.g., inversely proportional to link capacity).
  • OSPF messages carried directly by IP (protocol 89).
  • Uses HELLO messages and checks network connectivity.
  • Provides security via simple (password) and MD5 authentication.
  • Supports multiple same-cost paths and unicast/multicast routing (MOSPF).

OSPF Hierarchy

  • OSPF areas enhance routing performance within large ASs with a hierarchical structure.
  • Backbone area is responsible for inter-area packet routing.
  • Area border routers handle communication within and outside areas.

Routing Oscillations and Count-to-Infinity

  • Routing oscillations can occur due to congestion or delay-based metrics.
  • These occur when network link costs involve traffic load since those are not symmetrical.
  • The count-to-infinity problem can arise in DV routing, causing loops in routes as link costs fluctuate.

Poisoned Reverse

  • A technique mitigating the count-to-infinity problem in DV routing.
  • Routers incorrectly advertise cost to infinity to help prevent routing loops.
  • Message Complexity: LS requires O(n*e) messages, while DV exchanges information between neighbors.
  • Speed of Convergence: DV can be slower due to iterative updates and potential routing loops (count-to-infinity).
  • Robustness: LS is more robust to failures because route calculations are generally isolated within areas. DV's route calculations aren't isolated.

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Computer Networks Lecture 4.2 PDF

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Test your understanding of the control plane in computer networks with this quiz. Explore routing protocols, algorithms, and the interaction between control planes and routers. Perfect for students and professionals looking to deepen their knowledge in network architecture.

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