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Questions and Answers

What is the purpose of periodically passing copies of a routing table from router to router?

To communicate topology changes immediately (correct)

To update the routing tables with new information

To reduce the number of hops in the subnet

To increase the time delay in milliseconds

What is another name for the distance vector routing algorithm?

The Link State algorithm

Dijkstra's algorithm

The distributed Bellman-Ford routing algorithm (correct)

The Path Vector algorithm

What is contained in each entry of a routing table in distance vector routing?

The metric used and the number of hops to the destination

The IP address of the destination and the metric used

The preferred outgoing line and an estimate of the time or distance to that destination (correct)

The preferred outgoing line and the IP address of the destination

What is one of the metrics that can be used in distance vector routing?

Number of hops Signup and view all the answers

How does a router measure the delay in milliseconds if the metric is delay?

By sending ECHO packets that the receiver just time-stamps and sends them back Signup and view all the answers

What is the name of the algorithm used in the Internet under the name RIP?

Distance vector routing algorithm Signup and view all the answers

What is the name of the researchers who developed the distance vector routing algorithm?

Bellman and Fulkerson Signup and view all the answers

What was the original routing algorithm used in ARPANET?

Distance vector routing algorithm Signup and view all the answers

What is the main limitation of static routing in large or complex networks?

It requires a lot of time to define and maintain static route table entries Signup and view all the answers

What is the primary function of a default route?

To forward packets to a last resort outlet Signup and view all the answers

What is the primary function of a HELLO packet in link-state routing?

To learn who its neighbors are and their network addresses Signup and view all the answers

What happens to static routes in the routing table if a destination is down?

The static route remains in the routing table Signup and view all the answers

What type of network topologies were Distance Vector Protocols mainly designed for?

Small Signup and view all the answers

What is the main problem with the Distance Vector Routing algorithm?

It does not take line bandwidth into account when choosing routes Signup and view all the answers

What is the term 'Distance Vector' derived from?

The fact that the protocol includes a vector of distances (hop counts) Signup and view all the answers

What is the main difference between static and dynamic routing?

Static routing is manual, while dynamic routing is automatic Signup and view all the answers

What is the purpose of step 3 in the link-state routing process?

To construct a packet telling all that has just been learnt Signup and view all the answers

How do Distance Vector Protocols treat low speed links and high-speed links?

They treat low speed links equally or sometimes prefer them over high-speed links Signup and view all the answers

Why was the Distance Vector algorithm replaced?

It did not take line bandwidth into account and took too long to converge Signup and view all the answers

What is the purpose of a default outlet router?

To act as a last resort outlet for unknown destinations Signup and view all the answers

What type of algorithm is link-state routing also known as?

Shortest Path First (SPF) algorithm Signup and view all the answers

What is the finite limit of hops in Distance Vector Protocols after which a route is considered unreachable?

15 Signup and view all the answers

What happens to dynamic routes in the routing table if a destination is down?

The dynamic route is removed from the routing table Signup and view all the answers

What is one deficiency of Distance Vector Protocols?

They rely on hop counts Signup and view all the answers

What is the primary advantage of default routing?

It is used for networks with a single exit point Signup and view all the answers

What is placed in a router's routing table when it learns about other networks?

Each of the other network entries learnt from the other router Signup and view all the answers

How do routers exchange network numbers in Distance Vector Protocols?

Via periodic broadcasts of the entire routing table Signup and view all the answers

What is the first task of a router when it is booted?

To learn who its neighbors are and their network addresses Signup and view all the answers

What is the main characteristic of dynamic routing?

It is automatic and dependent on the network state Signup and view all the answers

What happens when a route exceeds the finite limit of hops in Distance Vector Protocols?

The route is considered unreachable Signup and view all the answers

What is the outcome of the 5-step process in link-state routing?

A complex database of topology information Signup and view all the answers

What is a consequence of the reliance on hop counts in Distance Vector Protocols?

Inefficient routing behavior may occur Signup and view all the answers

What happens to the routing table in large networks?

It becomes very hard to maintain Signup and view all the answers

What is a characteristic of D-V protocols?

They are flat and lack hierarchy Signup and view all the answers

What do routers exchange in Link State protocols?

Link states Signup and view all the answers

What do routers build in Link State protocols?

Their own routing tables Signup and view all the answers

What is the purpose of IP Routing protocols?

To determine the path that data follows Signup and view all the answers

What is the role of routers in IP Routing?

They perform traffic directing functions Signup and view all the answers

What is the term for the set of protocols that determine the path that data follows?

IP Routing Signup and view all the answers

What is the purpose of a routing protocol?

To specify how routers communicate with each other to distribute information Signup and view all the answers

What is the main benefit of planning an addressing scheme in a network?

Easier addition of routers in the future Signup and view all the answers

What is a characteristic of routed protocols?

They define the format and use of fields within a packet Signup and view all the answers

What is the purpose of a routing protocol?

To provide mechanisms for sharing routing information Signup and view all the answers

What is an example of a routed protocol?

IP Signup and view all the answers

Why do networks tend to use hierarchical routing as they grow in size?

Because it becomes impossible to have every router keep an entry of every other router Signup and view all the answers

What is static routing?

A method of routing that is set up manually in the router Signup and view all the answers

Why is centralised addressing authority important?

To prevent address conflicts Signup and view all the answers

What is the main goal of routing protocols in IP routing?

To select the least-cost path to the destination Signup and view all the answers

What is a major disadvantage of dynamic routing?

It tries to force dynamic routing on situations that do not really need it, wasting bandwidth and effort Signup and view all the answers

What is the benefit of designing an addressing scheme that will work with routing?

It allows for easier addition of routers in the future Signup and view all the answers

What is the main difference between routing and bridging?

Routing is used at the IP level, while bridging is used at the Data Link Layer Signup and view all the answers

What is the primary function of routing algorithms and protocols?

To make decisions about network paths Signup and view all the answers

Why are static routing configurations considered stable?

Because they are less prone to changes Signup and view all the answers

What happens as networks keep on growing in size?

Routing tables grow proportionately Signup and view all the answers

What is similar to how routing is done in a telephone network?

Hierarchical routing Signup and view all the answers

Why is dynamic routing not always the best option?

It tries to force dynamic routing on situations that do not really need it Signup and view all the answers

What is the term often referred to as the process of neighbour notification?

Neighbour notification Signup and view all the answers

What do routers transmit on the network in link-state routing?

Link State Packets (LSPs) Signup and view all the answers

What is constructed by routers in link-state routing?

Topological databases Signup and view all the answers

What algorithm is used by routers to construct the logical topology of shortest paths?

Dijkstra algorithm Signup and view all the answers

What is the purpose of the routing table in link-state routing?

To switch packet traffic Signup and view all the answers

What is compared in several key areas in Table 1?

Link-state routing and distance vector routing Signup and view all the answers

What do routers use to determine the shortest path to each other network?

SPF algorithm Signup and view all the answers

What is the outcome of the link-state routing process?

Switching of packet traffic Signup and view all the answers

What is the primary difference between link-state routing algorithms and distance vector routing algorithms?

The knowledge of distant routers and their interconnections Signup and view all the answers

What is the purpose of link-state network discovery mechanisms?

To create a common picture of the entire internetwork Signup and view all the answers

What do routers learn about in the first step of link-state network discovery?

Their neighbours and directly connected networks Signup and view all the answers

Which of the following protocols uses a link-state algorithm?

OSPF Signup and view all the answers

What is the main advantage of link-state routing algorithms?

They provide a more accurate view of the network Signup and view all the answers

What is the primary function of a router in the distance vector routing algorithm?

To receive routing tables from its neighbouring routers Signup and view all the answers

What is the relationship between link-state routers in a network?

They share a common view of the entire internetwork Signup and view all the answers

What is the primary characteristic of the distance vector routing algorithm?

It accumulates network distances to maintain a database of network topology Signup and view all the answers

What is the main limitation of the distance vector routing algorithm?

It does not allow routers to know the exact topology of an internetwork Signup and view all the answers

What is the outcome of link-state network discovery?

A common picture of the entire internetwork is created Signup and view all the answers

What is the purpose of adding a distance vector number to the routing table?

To increase the distance vector, thereby increasing the hop count Signup and view all the answers

What is a characteristic of link-state routing protocols?

They are widely used in actual networks Signup and view all the answers

What is the similarity between distance vector information and highway signs?

Both indicate the distance to the destination Signup and view all the answers

What is the outcome of the step-by-step process of distance vector routing updates?

The algorithm accumulates network distances to maintain a database of network topology Signup and view all the answers

What happens when a router receives a routing table from its neighbouring router?

It adds a distance vector number to the routing table and passes it to its other neighbouring router Signup and view all the answers

What is the primary role of distance vector routing updates?

To maintain a database of network topology information Signup and view all the answers

What is the primary function of Router 1 when a packet destined for network 100.1.0.0 arrives?

To pass the packet to the best network along the path Signup and view all the answers

What is represented as a direction to a destination network by a router?

The best network along the path Signup and view all the answers

What is the function of interface S0 in Router 1?

To connect to network 100.1.0.0 Signup and view all the answers

What is the next hop for a packet destined for network 100.4.0.0 in Router 1?

Router 2 through interface S2 Signup and view all the answers

What is the purpose of a router in a network?

To connect multiple networks together Signup and view all the answers

What is the result when a packet arrives at a router and the best path is determined?

The packet is sent to the next hop along the path Signup and view all the answers

What is the role of a router when a packet is destined for a network that is not directly connected?

To send the packet to the next hop along the path Signup and view all the answers

What is the primary function of router configuration?

To determine the best path for packet forwarding Signup and view all the answers

What is a key assumption of routing in IP networks?

Addresses convey partial information about a host's location Signup and view all the answers

What is the primary goal of subnetting?

To reduce the size of routing tables Signup and view all the answers

Which of the following is NOT a design plan for addressing in IP networks?

Dynamic Host Configuration Protocol (DHCP) Signup and view all the answers

What is the main limitation of static routing in large networks as mentioned in the content?

It is not scalable Signup and view all the answers

What happens to the routing table in large networks?

It grows proportionately Signup and view all the answers

What is a key benefit of using subnetting in IP networks?

Greater flexibility in network design Signup and view all the answers

Why do networks tend to use hierarchical routing as they grow in size?

To make routing more efficient Signup and view all the answers

What is the primary function of a router in IP networks?

To forward packets based on destination addresses Signup and view all the answers

Which of the following is a characteristic of IP Address Classes?

Hierarchical addressing structure Signup and view all the answers

What is the primary function of a routing protocol?

To determine the best path for data to follow Signup and view all the answers

What is the primary advantage of using CIDR?

Increased scalability and flexibility in network design Signup and view all the answers

What is the purpose of IP routing protocols?

To determine the best path for data to follow Signup and view all the answers

What is a key requirement for implementing routing in IP networks?

A centralised addressing authority Signup and view all the answers

What happens when a network grows in size?

Routing tables grow proportionately Signup and view all the answers

What is the benefit of designing an addressing scheme that will work with routing?

It makes routing more efficient Signup and view all the answers

What is a major disadvantage of dynamic routing?

It consumes a lot of bandwidth and memory Signup and view all the answers

What is the primary function of a network switch?

To appear as part of the wire and introduce no resistance, no attenuation, no delay Signup and view all the answers

How do routers determine the next-hop address to which a packet should be delivered?

By consulting a routing table to determine the next-hop address Signup and view all the answers

What is the key difference between a layer 2 switch and a layer 3 switch?

Layer 2 switches bridge, while layer 3 switches route Signup and view all the answers

What is the benefit of using special silicon chips in network switches?

They reduce the packet processing time and increase network efficiency Signup and view all the answers

What is the primary objective of IP routing?

To examine the destination IP address of a packet and determine the next-hop address Signup and view all the answers

What is the role of routers in IP routing?

To forward packets from one network to another based on routing tables Signup and view all the answers

What is the key difference between static and dynamic routing?

Static routing is manual, while dynamic routing is automatic Signup and view all the answers

What is the primary goal of routing in a network?

To select the most optimal path for packet transmission Signup and view all the answers

What is the primary advantage of IP routing?

It allows for efficient routing of packets between networks Signup and view all the answers

What are the two basic functions employed by a router to relay a packet?

Path determination and switching Signup and view all the answers

What is the main limitation of routing techniques that prioritize packets between adjacent stations?

Lack of fairness to distant stations Signup and view all the answers

What is the primary function of a routing table in a router?

To determine the most optimal path for packet transmission Signup and view all the answers

What is the main goal of optimizing routing in a network?

To minimize overhead processing required Signup and view all the answers

What is the primary advantage of using routing techniques that prioritize packets between adjacent stations?

Increased throughput between adjacent stations Signup and view all the answers

What is the primary role of a router in IP routing?

To forward packets based on network layer addresses Signup and view all the answers

What is the main consequence of relying on hop counts in routing techniques?

Limited network scalability Signup and view all the answers

Study Notes

Network Reachability and Routing

Network reachability in static routing is not dependent on the existence and state of the network itself.

Static Routing

Static routes remain in the routing table regardless of the destination's state (up or down).
Traffic is still sent towards the destination even if it's down.
Static routing is not suitable for large or complex networks due to the time required to define and maintain static route table entries.

Default Routing

Default routing is a "last resort" outlet for traffic to destinations unknown to the local router.
A default route is a path on which a router should forward a packet if it does not have specific knowledge about the packet's destination.

Dynamic Routing

Dynamic routing refers to routes being learned via an internal or external routing protocol.
Network reachability is dependent on the existence and state of the network.
If a destination is down, the route disappears from the routing table, and traffic is not sent towards the destination.
Dynamic routing enables routers to build their routing tables automatically and make appropriate forwarding decisions.

Distance Vector Routing

Each router maintains a routing table containing one entry for each router in the subnet.
The entry consists of two parts: the preferred outgoing line/port to use for that destination and an estimate of the time or distance to that destination.
The metric used might be the number of hops, time delay in milliseconds, total number of packets queued along the path, or something similar.

Link State Routing

Link State Routing replaced Distance Vector Routing in 1979.
The algorithm involves 5 steps: discovering neighbors, measuring delay or cost, constructing a packet, sending the packet to other routers, and computing the shortest path to every other router.
Link-state routing algorithms maintain a complex database of topology information.

Distance Vector Protocols

Distance Vector Protocols, such as RIP Version 1, were designed for small network topologies.
The protocol includes a vector of distances (hop counts) in its routing updates.
Low-speed links are treated equally or sometimes preferred over high-speed links, depending on the calculated hop count.
Distance Vector Protocols have a finite limit of hops (15) after which a route is considered unreachable.
The reliance on hop counts is one deficiency of distance vector protocols.
Routing information gets updated through periodic broadcasts of the entire routing table, which can be inefficient in large networks.

Link State Protocols

Link State Protocols work on the basis that routers exchange information elements called link states, which carry information about links and nodes.
Routers do not exchange routing tables; instead, each router builds its own routing table using the exchanged link states.

IP Routing

IP Routing is an umbrella term for the set of protocols that determine the path data follows across multiple networks from its source to its destination.
IP Routing protocols enable routers to build up a forwarding table that correlates final destinations with next-hop addresses.
A routing protocol specifies how routers communicate with each other to distribute information that enables them to select routes between nodes on a computer network.

Enforcement of IP Addressing

A plan for IP addressing must be enforced, and addressing authority must be centralized.
A design is useless unless addresses are assigned in accordance with it.
Planning for routing is essential, even if it's not used initially, to ensure a scalable and organized addressing scheme.

Routed Protocols

A routed protocol is a protocol that contains sufficient network-layer addressing information for user traffic to be directed from one network to another.
Routed protocols define the format and use of the fields within a packet.
Examples of routed protocols include IP and Novell's IPX.

Routing Protocols

A routing protocol provides mechanisms for sharing routing information.
Routing protocol messages move between routers, allowing them to communicate with other routers to update and maintain routing tables.
Routing protocol messages do not carry end-user traffic from network to network.

Types of Routing

There are three types of routing: static, default, and dynamic.

Static Routing

Static routing refers to routes to destinations being set up manually in the router.
It is a stable but not very flexible configuration.
Static and default routing are not necessarily outdated and can be useful in certain situations.

Dynamic Routing

Dynamic routing is a more flexible and scalable approach, but it can be more complex and resource-intensive.
It is not necessary to use dynamic routing in all situations, and it can be a waste of bandwidth, effort, and money.

Routing Algorithms

Routing algorithms and protocols form the core of the internet, as they make decisions about routing.
Network engineers assign costs to network paths, and routing protocols select the least-cost path to the destination.
Examples of routing algorithms include distance vector and link-state routing.

Distance Vector Routing

Distance vector routing algorithms do not allow a router to know the exact topology of an internetwork.
Distance vector information is similar to the information found on signs at a highway intersection.
Examples of distance vector routing protocols include RIP.

Link-State Routing

Link-state routing algorithms maintain full knowledge of distant routers and how they interconnect.
Examples of link-state routing protocols include NLSP, OSPF, and IS-IS.
Link-state routing is widely used in actual networks.

Link-State Network Discovery

Link-state network discovery mechanisms are used to create a common picture of the entire internetwork.
All routers employing the link-state routing algorithm share this common view of the internetwork.
Link-state network discovery proceeds through neighbor notification, transmission of LSPs, and construction of topological databases.

Comparison of Distance Vector Routing and Link-State Routing

Distance vector routing can be compared to link-state routing in several key areas, including:
- Complexity and scalability
- Convergence time
- Network topology knowledge
- Reaction to network changes

IP Routing Principles

IP Routing is a process that sends packets from a host on one network to another host on a different remote network.
It helps to examine the destination IP address of a packet, determine the next-hop address, and forward it.

Routing and Network Layer Addresses

Routers relay a packet from one data link to another using two basic functions: path determination and switching functions.
Path determination function enables the router to select the most appropriate interface for forwarding a packet.
Switching function enables a router to accept a packet on one interface and forward it on a second interface.
Routing assumes that addresses have been assigned to network elements to facilitate data delivery.

Routing Table

Routing tables are used by routers to determine the next-hop address to which the packet should be delivered.
The routing table consists of a list of network addresses and corresponding interface numbers.

Routing Algorithms

Routing algorithms and protocols form the core of the Internet, as they make all the decisions.
Network engineers assign costs to network paths, and routing protocols select the least-cost path to the destination.

Types of Routing

Static routing: a plan must exist by which addresses are assigned, and the design plan must be implemented in switching nodes.
Dynamic routing: routers use dynamic routing to update their routing tables, and it is more flexible than static routing.
Default routing: it is not as flexible as dynamic routing, but it is more stable.

Switching

A networking switch is designed to behave like a wire when relaying data signals.
Switches must implement a normal path selection algorithm, and they can forward packets directly from source to destination without passing through RAM buffers.
Switches are faster than normal bridges and routers, and they use special silicon chips to forward packets.

Learning Objectives

Understand the concept of switching and routing.
Understand routed and routing protocols.
Identify types of routing: static, default, dynamic.
Understand routing algorithms.
Understand distance vector and link state routing.

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Description

Learn about static routing in computer networks, its advantages and limitations, and how it differs from dynamic routing. Test your understanding of static route tables and their maintenance.