Chapter 5

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Questions and Answers

What can lead to erroneous routing information being advertised in a distance-vector routing protocol?

  • A node can broadcast an incorrect cost related to its own links.
  • A packet being dropped during an LS broadcast.
  • A malfunctioning router advertising incorrect least-cost paths. (correct)
  • All routers executing the same routing algorithm.

Which characteristic is true for link-state routing compared to distance-vector routing?

  • Link-state routing allows for quicker propagation of updates.
  • Link-state routing isolates route calculations, enhancing robustness. (correct)
  • Link-state routing is inherently less robust than distance-vector routing.
  • Link-state routing results in completely interdependent route calculations.

What does the scale issue in network routing refer to?

  • The difficulty of managing communications as the number of routers increases. (correct)
  • The ability of routing algorithms to function with minimal overhead.
  • The ease of storing routing information in small networks.
  • The potential of routers to execute multiple algorithms simultaneously.

What is a significant risk associated with using distance-vector routing protocols?

<p>Incorrect route calculations can spread throughout the network. (B)</p> Signup and view all the answers

How does link-state routing enhance the robustness of network routing?

<p>By isolating routing updates to prevent widespread errors. (C)</p> Signup and view all the answers

What triggers a router to broadcast link-state information?

<p>A change in a link’s cost or up/down status. (B)</p> Signup and view all the answers

Which routing protocol is used for routing packets across multiple ASs?

<p>Border Gateway Protocol (BGP). (A)</p> Signup and view all the answers

What mechanism ensures intra-AS routing protocols determine the route a packet follows?

<p>The specific intra-AS routing protocol being used. (B)</p> Signup and view all the answers

What is one of the key benefits of periodic updating of link state advertisements?

<p>Enhanced robustness of the link state algorithm. (C)</p> Signup and view all the answers

Which of the following statements about OSPF is true?

<p>OSPF messages are routed to an area border router. (D)</p> Signup and view all the answers

In which situation would the same inter-AS routing protocol need to be used by multiple ASs?

<p>To ensure seamless communication between the ASs. (B)</p> Signup and view all the answers

What is the primary function of BGP in relation to ISPs?

<p>BGP acts as a decentralized protocol that interconnects ISPs. (A)</p> Signup and view all the answers

How does a router determine the forwarding table entries for destinations outside its AS?

<p>By leveraging BGP to obtain prefix reachability information. (A)</p> Signup and view all the answers

What is the primary function of the OSPF protocol within an autonomous system?

<p>It performs intra-autonomous system routing. (D)</p> Signup and view all the answers

Which algorithm does OSPF use to determine the shortest path in the network?

<p>Dijkstra's least-cost path algorithm (A)</p> Signup and view all the answers

How does OSPF generate a routing table?

<p>By using a complete topological map of the autonomous system. (B)</p> Signup and view all the answers

What does the 'Open' in Open Shortest Path First (OSPF) signify?

<p>The routing protocol's specifications are publicly available. (B)</p> Signup and view all the answers

What role do forwarding tables play in BGP?

<p>They store routing information for incoming packets. (C)</p> Signup and view all the answers

What role do network administrators play in the OSPF protocol?

<p>They configure individual link costs for optimal routing. (A)</p> Signup and view all the answers

BGP allows a subnet to do what with respect to the rest of the Internet?

<p>Advertise its existence. (D)</p> Signup and view all the answers

What characterizes link-state protocols like OSPF?

<p>They use a distributed database to share routing information. (A)</p> Signup and view all the answers

Why is BGP considered essential for understanding the Internet deeply?

<p>It is integral to the interconnectivity of ISPs. (B)</p> Signup and view all the answers

What does link-state information in OSPF help routers to achieve?

<p>Build a complete network topology graph. (C)</p> Signup and view all the answers

What is a common misconception about OSPF routing paths?

<p>They require constant manual adjustment by administrators. (D)</p> Signup and view all the answers

What is the main challenge associated with storing routing information at each router in a large network?

<p>Enormous amounts of memory required for storage (D)</p> Signup and view all the answers

What can lead to a failure of convergence in distance-vector algorithms within large networks?

<p>Large number of routers creating update overhead (B)</p> Signup and view all the answers

Why do ISPs prefer to organize routers into autonomous systems (ASs)?

<p>To enable autonomy in network management and routing algorithms (B)</p> Signup and view all the answers

How is an autonomous system (AS) uniquely identified?

<p>By its globally unique autonomous system number (ASN) (B)</p> Signup and view all the answers

What plays a crucial role in managing updates related to routers in an AS?

<p>The implementation of consistent routing protocols (B)</p> Signup and view all the answers

Which of the following is NOT typically a goal of an ISP when managing its network?

<p>To unify all routers under a common protocol (D)</p> Signup and view all the answers

What is one of the major concerns when broadcasting connectivity updates among routers?

<p>The significant bandwidth consumed during updates (D)</p> Signup and view all the answers

The Border Gateway Protocol (BGP) is used to route packets within a single autonomous system.

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

Open Shortest Path First (OSPF) is classified as an intra-AS routing protocol.

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

OSPF periodically broadcasts link-state information only when there is a change in the link's cost.

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

Routing among multiple ASs requires that all ASs involved use the same inter-AS routing protocol.

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

OSPF advertisements are routed to area border routers for intra-area routing before reaching the final destination.

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

Periodic updates of link-state advertisements enhance the resilience of the link-state algorithm in OSPF.

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

ICMP is primarily used for managing routing among autonomous systems.

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

A router will only broadcast link-state information if it detects a change in the link's up/down status.

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

All routers within the same autonomous system (AS) must implement different routing algorithms.

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

An autonomous system is identified by a unique number assigned by ICANN regional registries.

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

ISPs typically desire to have complete control over the routing protocols used within their networks.

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

Broadcasting connectivity updates among routers in a large network has minimal overhead.

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

Distance-vector algorithms are guaranteed to converge in the context of large autonomous systems.

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

Some ISPs break their networks into multiple autonomous systems for better management.

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

ICMP is primarily concerned with the advertisements of routing updates within an AS.

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

An autonomous system can consist of a group of routers under the same administrative control.

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

A distance-vector algorithm can effectively handle enormous amounts of routing information without any issues.

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

BGP operates as an intra-AS routing protocol for managing traffic within a single autonomous system.

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

An intra-autonomous system routing protocol is OSPF.

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

The Dijkstra’s algorithm used in OSPF helps all routers in an autonomous system to work independently without sharing information.

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

ISPs utilize BGP to obtain prefix reachability information from neighboring ASs.

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

Intra-AS routing protocols determine the forwarding table entries for destinations outside the AS.

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

The BGP protocol is primarily designed to enhance the reachability and scalability of inter-AS routing across the Internet.

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

Link costs in OSPF are fixed and cannot be modified by network administrators.

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

ICMP is directly involved in determining prefix reachability within the BGP protocol.

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

OSPF routing uses a distance-vector approach to determine the best paths for data packets.

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

The term 'intra-AS' refers to routing that occurs within a single autonomous system.

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

The 'Open' in OSPF signifies that the protocol is proprietary and not publicly available.

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

A router within an AS only uses BGP to route packets to both internal and external destinations.

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

BGP helps routers advertise the existence of subnets to the rest of the Internet.

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

IS-IS is a competition-based routing protocol specifically designed for inter-AS routing.

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

Traffic flows in OSPF according to the routing tables computed by a distance-vector algorithm.

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

Intra-AS routing protocols are responsible for exchanging routing information between different autonomous systems.

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

Distance-vector routing protocols can lead to incorrect least-cost path advertisements due to the diffusion of incorrect calculations throughout the network.

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

The Internet Control Message Protocol (ICMP) is primarily used for sending routing updates between routers in an autonomous system.

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

The scale of today's Internet poses significant challenges to the efficiency of routing protocols due to the sheer number of interconnected routers.

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

What is a key challenge for routers executing the same algorithm in a large network environment?

<p>Overhead in communicating and storing routing information (D)</p> Signup and view all the answers

In the context of inter-AS routing, what implication arises from the potential for a node to advertise incorrect least-cost paths?

<p>Traffic flooding can result from erroneous routing information. (C)</p> Signup and view all the answers

Which statement accurately describes the role of ICMP within the scope of network routing?

<p>ICMP is used for error reporting and operational queries about routing. (B)</p> Signup and view all the answers

The intra-AS routing protocol OSPF primarily employs which algorithm to determine the shortest path?

<p>Dijkstra's Algorithm (A)</p> Signup and view all the answers

What is the primary advantage of periodic link-state advertisements in OSPF?

<p>They enhance the robustness of the routing algorithm. (B)</p> Signup and view all the answers

Which statement accurately describes the relationship between OSPF and autonomous systems?

<p>OSPF operates as an intra-AS routing protocol. (B)</p> Signup and view all the answers

When routing a packet between different ASs, what protocol must be implemented by all communicating ASs?

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

What distinguishes inter-AS routing protocols such as BGP from intra-AS protocols like OSPF?

<p>Inter-AS protocols facilitate coordination among multiple ASs. (B)</p> Signup and view all the answers

Which of the following best describes ICMP's primary role in network communication?

<p>Providing error messages and operational information. (D)</p> Signup and view all the answers

Which of the following statements is incorrect regarding the routing of packets across multiple ASs?

<p>BGP does not require ASs to use the same routing protocol. (C)</p> Signup and view all the answers

What aspect of OSPF contributes to its complexity compared to simpler routing protocols?

<p>The necessity of maintaining a complete topology map of the network. (A)</p> Signup and view all the answers

In the context of BGP, what does the term 'autonomous system' refer to?

<p>A group of routers managed by a single organization. (D)</p> Signup and view all the answers

What is the primary benefit of organizing routers into autonomous systems (ASs) for ISPs?

<p>It enables administrative control over routing decisions. (A)</p> Signup and view all the answers

Which statement accurately describes the function of the Border Gateway Protocol (BGP) in relation to inter-AS routing?

<p>BGP facilitates routing packets between disparate autonomous systems. (A)</p> Signup and view all the answers

What is one major consequence of the overhead in broadcasting link updates in large networks?

<p>It leads to inefficient bandwidth usage and potential network congestion. (B)</p> Signup and view all the answers

How do routers within the same autonomous system typically handle routing information?

<p>They run the same routing algorithm and share internal routing data. (B)</p> Signup and view all the answers

How is an autonomous system (AS) identified uniquely?

<p>By its own unique autonomous system number (ASN). (B)</p> Signup and view all the answers

What is a common characteristic of routing among ISPs in terms of network independence?

<p>ISPs operate their networks autonomously while connecting to others. (D)</p> Signup and view all the answers

Which role does ICMP (Internet Control Message Protocol) primarily fulfill in network routing?

<p>It assists with error reporting and operational diagnostics. (C)</p> Signup and view all the answers

What is a significant challenge regarding distance-vector routing algorithms in large networks?

<p>They can struggle to converge due to high complexity and volume. (C)</p> Signup and view all the answers

What differentiates an intra-AS routing protocol like OSPF from inter-AS protocols like BGP?

<p>Intra-AS protocols manage routes within a single AS, while inter-AS protocols handle multiple ASs. (D)</p> Signup and view all the answers

What is the primary purpose of BGP in the context of inter-AS routing?

<p>To allow the advertisement of subnet reachability information (D)</p> Signup and view all the answers

Which statement accurately defines the function of a forwarding table in a BGP-enabled router?

<p>It directs packets to CIDRized prefixes representing multiple subnets. (D)</p> Signup and view all the answers

How does BGP differ from traditional intra-AS routing protocols?

<p>BGP provides asynchronous and decentralized routing capabilities. (A)</p> Signup and view all the answers

What type of information does an AS commonly exchange with its neighbors using BGP?

<p>Prefix reachability information (C)</p> Signup and view all the answers

In an inter-AS routing context, what does BGP primarily route packets towards?

<p>CIDRized prefixes representing subnets (D)</p> Signup and view all the answers

What is a crucial function of the Internet Control Message Protocol (ICMP) within the realm of routing?

<p>To send error messages and operational information (B)</p> Signup and view all the answers

ICMP primarily operates at which level of the Internet Protocol Suite?

<p>Network layer (D)</p> Signup and view all the answers

Which factor directly influences the link costs in OSPF?

<p>Manual configuration set by network administrators (C)</p> Signup and view all the answers

Which of the following statements best describes the Open in Open Shortest Path First (OSPF)?

<p>It refers to the open-source nature of the OSPF routing specification. (A)</p> Signup and view all the answers

What is the primary advantage of using Dijkstra’s algorithm in OSPF?

<p>It minimizes the overall cost for routing paths within the network. (D)</p> Signup and view all the answers

What distinguishes OSPF from other routing protocols in the context of integrated network systems?

<p>The utilization of link-state information dissemination. (C)</p> Signup and view all the answers

Which protocol is primarily concerned with managing error messages and operational information within an autonomous system?

<p>Internet Control Message Protocol (ICMP) (C)</p> Signup and view all the answers

In the context of routing protocols, what is one major drawback of distance-vector algorithms when compared to link-state protocols like OSPF?

<p>They can suffer from routing loops and slow convergence time. (A)</p> Signup and view all the answers

Flashcards

OSPF

An intra-AS routing protocol used for routing packets within a single autonomous system.

BGP

An inter-autonomous system routing protocol used for routing between different autonomous systems.

Autonomous System (AS)

A group of internet networks under the same administration.

Intra-AS Routing

Routing within a single autonomous system.

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Inter-AS Routing

Routing between different autonomous systems.

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Link State Advertisement

Broadcasted information about a link's state, used by OSPF routing.

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Link State

The status (up/down) and cost of a communication link.

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Routing

The process of determining the path a packet takes through a network.

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Autonomous System (AS)

A group of routers under the same administrative control, often an ISP's network.

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Administrative Autonomy

The ability of an ISP to manage its own network and routing independently.

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Routing Complexity

The difficulty of calculating packet paths across a huge network, requiring simplification.

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Autonomous System Number (ASN)

A unique identifier for each autonomous system.

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Internet Structure

A network of autonomous systems (ISPs) that communicate.

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Reducing Routing Overhead

Strategies employed to decrease the computational cost of routing.

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Large Network Issues

Challenges associated with routing in massive networks like the Internet.

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Inter-AS Routing

Protocols used to manage information exchange across independent networks.

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Intra-AS Routing

Manage routing information within a single AS.

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ICANN

Organization in charge of managing Internet addresses and AS Numbers (ASN).

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Intra-Autonomous System Routing

Routing protocol operating within a single autonomous system (AS).

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OSPF

Open Shortest Path First; a common link-state routing protocol.

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Link-State Protocol

Routing protocol where routers share link information.

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Flooding

Process of disseminating routing information to all routers.

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Dijkstra's Algorithm

Algorithm for finding shortest paths in a graph.

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Topological Map

Complete representation of the network's structure.

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Shortest Path Tree

Tree showing the optimal paths from a router to other ones.

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Link Cost

Numerical value representing the cost of traversing a link.

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Network Administrator

Person responsible for configuring network settings, including link costs.

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Autonomous System (AS)

Group of networks under a single administrative entity.

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BGP's Role

BGP connects Internet Service Providers (ISPs) by routing packets to prefixes (subnets) rather than specific destinations.

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BGP Destination

BGP routes packets to a CIDRized prefix (e.g., 138.16.68/22), a collection of IP addresses.

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BGP Forwarding Table

A router's table mapping prefixes to network interfaces.

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Inter-AS Routing

Routing between autonomous systems (groups of networks under the same administration).

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Autonomous System (AS)

A collection of interconnected networks under the control of a single organization or entity.

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Prefix Reachability

Information about whether a specific subnet (prefix) is accessible.

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CIDRized Prefix

A means of representing a block of IP addresses using a combination of network address and subnet mask (e.g., 138.16.68/22).

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Intra-AS Routing

Routing within a single autonomous system.

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Forwarding Table

A table in a router storing information on how to forward packets.

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Decentralized Protocol

A protocol that has no single control point.

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LS Routing Algorithm

A routing algorithm where each router has a complete map of the network, allowing it to calculate its forwarding table independent of other routers.

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DV Routing Algorithm

A routing algorithm where routers exchange information about the costs of reaching destinations. Calculations rely on neighbors' information.

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Routing Information Error (DV)

Errors in advertised routing information, which potentially affect numerous nodes in a DV network.

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Routing Overhead

The computational cost of gathering, processing and storing routing information in a network.

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Scalability Issues in Routing

The difficulty of maintaining efficient routing in large networks due to the exponential increase in information requirements.

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OSPF

An intra-AS routing protocol used for routing within a single autonomous system.

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BGP

An inter-AS routing protocol for routing packets between autonomous systems.

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Autonomous System (AS)

A group of interconnected networks managed by a single organization.

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Intra-AS routing

Routing strategies for managing data packets within a single autonomous system.

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Inter-AS routing

Routing packets between different autonomous systems (e.g., ISP networks).

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Link State Advertisement

Information about link status and cost, used for routing.

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Link State

The status (up/down) and cost of a communication link.

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Routing

Determining the optimal path for data packets.

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Routing Complexity

The difficulty of finding efficient paths for data packets in a large network like the Internet.

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Autonomous System (AS)

A group of networks under a single administrative entity or organization, such as an ISP.

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Administrative Autonomy

The ability of an organization to manage its own network and routing as desired without outside interference.

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Routing Overhead

The computational effort to gather, process, and store routing information in a network.

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Autonomous System Number (ASN)

A unique identifying number for an autonomous system; allocated by ICANN.

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Internet Structure

The organized network of autonomous systems (ISPs) designed for scalable communication and interconnection.

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Scalability Issues in Routing

Challenges in handling routing in very large networks due to the need for vast amounts of information.

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Large Network Issues

Problems of storage and processing that arise in networks with countless routers trying to find the shortest path.

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Inter-AS Routing

The way routers in different autonomous systems communicate routing information.

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Reducing Routing Overhead

Strategies for minimizing the computation required to find paths in the network.

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Intra-Autonomous System Routing

Routing protocol used within a single autonomous system (AS).

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OSPF

Open Shortest Path First, a link-state routing protocol.

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Link-State Protocol

Routers share link information (status and cost).

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Flooding

Disseminating routing information to all routers.

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Dijkstra's Algorithm

Finds shortest paths in a graph.

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Topological Map

Complete network structure.

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Shortest Path Tree

Optimal paths from a router to all others.

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Link Cost

Numerical value representing link traversal expense.

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Network Administrator

Person responsible for setting up and managing link costs.

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Autonomous System (AS)

Group of networks under a single administration.

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LS Routing Algorithm

A routing algorithm where each router has a complete map of the network, allowing it to calculate its forwarding table independently of other routers.

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DV Routing Algorithm

A routing algorithm where routers exchange information about the costs of reaching destinations. Calculations rely on neighbors' information.

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Routing Overhead

The computational cost of gathering, processing, and storing routing information in a network.

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Scalability Issues in Routing

Difficulty maintaining efficient routing in large networks due to the exponential increase in information requirements.

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Routing Information Error (DV)

Errors in advertised routing information which potentially affect numerous nodes in a DV network.

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BGP's Role

BGP connects internet service providers (ISPs) by routing packets to prefixes (subnets), rather than specific destinations.

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BGP Destination

BGP routes packets to a CIDRized prefix (e.g., 138.16.68/22), a collection of IP addresses.

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BGP Forwarding Table

A router's table mapping prefixes to network interfaces.

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Inter-AS Routing

Routing between autonomous systems (groups of networks under the same administration).

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Autonomous System (AS)

A collection of interconnected networks under the control of a single organization or entity.

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Prefix Reachability

Information about whether a specific subnet (prefix) is accessible.

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CIDRized Prefix

A means of representing a block of IP addresses using a combination of network address and subnet mask (e.g., 138.16.68/22).

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Forwarding Table

A table in a router storing information on how to forward packets.

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Decentralized Protocol

A protocol that has no single control point.

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Intra-AS Routing

Routing within a single autonomous system.

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Intra-AS Routing

Routing within a single autonomous system (AS).

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Inter-AS Routing

Routing between different autonomous systems (ASs).

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Autonomous System (AS)

A group of networks under the same administrative control.

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BGP

Border Gateway Protocol; used for inter-AS routing.

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OSPF

Open Shortest Path First; used for intra-AS routing.

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Link State Advertisement

Information about a link's status and cost, used in OSPF.

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Link Cost

Numerical value representing the cost of traversing a link.

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Routing

Determining the best path for data packets across a network.

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Autonomous System (AS)

A group of routers under the same administrative control, often an ISP's network.

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Routing Overhead

The computational cost of gathering, processing and storing routing information.

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Administrative Autonomy

The ability of an ISP to manage its network independently.

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Routing Complexity (Large Networks)

The difficulty of calculating routes in large networks like the Internet.

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Autonomous System Number (ASN)

A globally unique identifier for each autonomous system.

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Intra-AS Routing

Routing methods to find the best path between routers within the same autonomous system.

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Inter-AS Routing

Routing that manages communications between different autonomous systems.

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Reducing Routing Overhead

Techniques used to decrease the computational cost of finding routes.

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Internet Structure

A network of autonomous systems organized for scalable communication

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Routing Information Error (DV)

Errors in advertised routing information that may affect many nodes.

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Intra-AS Routing

Routing protocols used for managing data packets within a single autonomous system (i.e., a group of connected networks under a single administrative entity).

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OSPF

Open Shortest Path First; a common link-state routing protocol used for intra-AS routing (specifically inside an autonomous system).

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Autonomous System (AS)

A group of internet networks under the same administration, often a single internet service provider(ISP).

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Link-State Protocol

A routing protocol where routers share information about link status and cost to all other routers in the autonomous system.

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Dijkstra's Algorithm

An algorithm for finding the shortest path between nodes in a graph; crucial for calculating best routes in OSPF.

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Link Cost

A numerical value assigned to a link to represent its cost or delay in a network.

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Topological Map

A complete diagram of a network's structure, including all routers and their connections.

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Shortest Path Tree

A tree representing the shortest paths from a designated router to every other router in the network based on cost (delay).

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Flooding

A process where routing information is disseminated throughout the entire network.

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Network Administrator

The person responsible for configuring network settings, including assigning link costs, thus impacting routing choices.

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LS Routing Algorithm

Each router has a complete network map, independently calculating its forwarding table.

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DV Routing Algorithm

Routers exchange cost information to destinations, calculations rely on neighbors' data.

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Routing Overhead

Computational cost of gathering, processing, and storing routing information in a network.

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Scalability Issues in Routing

Difficulties in maintaining efficient routing in large networks due to increasing information needs.

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Routing Information Error (DV)

Errors in advertised routing data can affect numerous nodes in a DV routing network.

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BGP's Role

BGP connects ISPs by routing packets to prefixes, not specific destinations.

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BGP Destination

BGP routes packets to CIDRized prefixes (e.g., 138.16.68/22), which represent a block of IP addresses.

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BGP Forwarding Table

A router's table mapping prefixes to interfaces for forwarding packets.

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Inter-AS Routing

Routing between autonomous systems (groups of networks under a single admin).

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Autonomous System (AS)

A collection of interconnected networks under one organization's control.

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Prefix Reachability

Information on whether a specific subnet (prefix) is accessible.

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CIDRized Prefix

A way to represent IP address ranges (e.g., 138.16.68/22).

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Forwarding Table

A router's table specifying how to forward packets.

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Decentralized Protocol

A protocol without a central control point.

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Intra-AS Routing

Routing within a single autonomous system (AS).

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Study Notes

Network Layer: Control Plane

  • This chapter covers the control-plane component of the network layer
  • This logic controls how a datagram is routed from source to destination
  • It also configures and manages network components and services
  • Routing algorithms are covered in Section 5.2, including traditional routing algorithms for computing least cost paths
  • Two widely deployed Internet routing protocols are OSPF (within a single ISP's network) and BGP (interconnecting networks)
  • SDN (software-defined networking) is covered in Section 5.5; it separates data and control planes and utilizes a controller service distinct from router forwarding functions.
  • Sections 5.6 and 5.7 cover ICMP (Internet Control Message Protocol) and SNMP (Simple Network Management Protocol), managing an IP network.

Introduction

  • The forwarding table and flow tables specify the data-plane forwarding (behavior of a router)
  • Control and data planes in networking
  • Per-router control (Figure 5.1)
  • Logically centralized control (Figure 5.2)

Routing Algorithms

  • Computing good (least cost) paths through a network of routers
  • Routing algorithms must consider policy issues and may be load-sensitive or load-insensitive
  • Centralized routing algorithm uses complete network knowledge
  • Decentralized (distance-vector) routing algorithm iterates in a distributed manner, with each node having limited information
  • Link-state (LS) Algorithm (Section 5.2.1)
  • Distance-Vector (DV) Algorithm (Section 5.2.2)
  • Graph modeling (Figure 5.3, etc)

Intra-AS Routing

  • OSPF (Open Shortest Path First) is a widely used intra-AS routing protocol
  • OSPF is a link-state protocol, using Dijkstra's algorithm to determine shortest paths. It uses flooding of link-state information
  • Scalability is an important issue for very large networks
  • Administrative autonomy and control of network operation (important for routing large networks)
  • OSPF link weights are managed for routing paths that meet traffic engineering goals.

Inter-AS Routing (BGP)

  • BGP (Border Gateway Protocol) is an inter-AS routing protocol
  • The router learns about reachability of networks
  • BGP is a decentralized, asynchronous protocol (in the distance-vector vein). Each router only has knowledge of its neighbors
  • Key BGP concept: CIDRized prefixes (for communication)
  • BGP route-selection algorithm: it chooses a route based on local preference, shortest AS path, and closest NEXT-HOP router
  • Routing policies are critical for inter-AS routing; policies can override other factors
  • hot potato routing is a technique to choose the best route by finding the shortest path with the least cost.

SDN Control Plane

  • SDN control plane manages packet forwarding and configuration of network devices
  • Three key attributes are defined: (1) Flow-Based Forwarding (2) Separation of Data Plane and Control Plane (3) Programmable Networks
  • Components of the SDN architecture (Figure 5.14): SDN Controller, Network Control Applications, and SDN Controlled Switches.
  • The OpenFlow protocol is used in SDN for communication between the controller and switched network devices
  • SDN controller manages flow tables in the switches, for example, when a link fails, the SDN controller dynamically changes the flow table entries in the affected switches.

ICMP and Network Management

  • ICMP (Internet Control Message Protocol) used for network-layer communication and error reporting
  • ICMP is for error reporting - examples include “destination unreachable”
  • ICMP messages are carried inside IP datagrams

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