Routing protocols allow routers to share information about networks and determine optimal paths between sources and destinations. Common routing protocols include RIP, OSPF, and BGP. Routers use routing tables containing network addresses, next hops, and interfaces to forward packets based on longest prefix matching of the destination address. Dynamic routing allows tables to automatically update when network changes occur.
This document discusses and compares two routing protocols: distance vector routing and link state routing. Distance vector routing involves each node sharing its routing table only with its neighbors, while link state routing involves each node having knowledge of the entire network topology. The document outlines the working principles, drawbacks like count to infinity, and pros and cons of each approach.
This document discusses error detection and correction techniques used in data transmission. It covers various types of errors that can occur during transmission and different coding schemes used for error detection and correction, including block coding, linear block coding, cyclic codes, and cyclic redundancy checks (CRCs). Specific examples are provided to illustrate how Hamming codes, parity checks, and CRCs can detect and correct single-bit and burst errors. Key concepts covered include redundancy, minimum Hamming distance, encoding/decoding processes, and the use of polynomials to represent binary words in CRC calculations.
This document summarizes key aspects of the transport layer:
- The transport layer provides logical communication between application processes running on different hosts and handles reliable data transfer.
- It provides both connection-oriented and connectionless services to the application layer. Quality of service parameters like throughput and delay can be negotiated.
- Transport layer protocols like TCP and UDP are described. TCP provides reliable byte-stream delivery using connections while UDP provides best-effort unreliable datagram delivery.
The document discusses various data link layer protocols. It begins by introducing stop-and-wait and sliding window protocols. It then provides an example of a stop-and-wait protocol where a frame is lost, leading the sender to retransmit a duplicate frame. Next, it discusses sliding window protocols and provides an example where the window allows multiple outstanding frames. Finally, it gives an example of a one-bit sliding window protocol that uses acknowledgments to control the window.
The transport layer provides efficient, reliable, and cost-effective process-to-process delivery by making use of network layer services. The transport layer works through transport entities to achieve its goal of reliable delivery between application processes. It provides an interface for applications to access its services.
Network devices like hubs, switches, and routers connect computers in a network and help manage traffic flow. Hubs broadcast all received data to all ports but have limited bandwidth. Switches can connect more devices than hubs and have features like VLANs. Routers connect different networks and use IP addresses to direct traffic. Other devices like firewalls, VPNs, and IDS/IPS provide network security functions.
Proactive routing protocol
Each node maintain a routing table.
Sequence number is used to update the topology information
Update can be done based on event driven or periodic
Observations
May be energy expensive due to high mobility of the nodes
Delay can be minimized, as path to destination is already known to all nodes.
This document discusses and compares two routing protocols: distance vector routing and link state routing. Distance vector routing involves each node sharing its routing table only with its neighbors, while link state routing involves each node having knowledge of the entire network topology. The document outlines the working principles, drawbacks like count to infinity, and pros and cons of each approach.
This document discusses error detection and correction techniques used in data transmission. It covers various types of errors that can occur during transmission and different coding schemes used for error detection and correction, including block coding, linear block coding, cyclic codes, and cyclic redundancy checks (CRCs). Specific examples are provided to illustrate how Hamming codes, parity checks, and CRCs can detect and correct single-bit and burst errors. Key concepts covered include redundancy, minimum Hamming distance, encoding/decoding processes, and the use of polynomials to represent binary words in CRC calculations.
This document summarizes key aspects of the transport layer:
- The transport layer provides logical communication between application processes running on different hosts and handles reliable data transfer.
- It provides both connection-oriented and connectionless services to the application layer. Quality of service parameters like throughput and delay can be negotiated.
- Transport layer protocols like TCP and UDP are described. TCP provides reliable byte-stream delivery using connections while UDP provides best-effort unreliable datagram delivery.
The document discusses various data link layer protocols. It begins by introducing stop-and-wait and sliding window protocols. It then provides an example of a stop-and-wait protocol where a frame is lost, leading the sender to retransmit a duplicate frame. Next, it discusses sliding window protocols and provides an example where the window allows multiple outstanding frames. Finally, it gives an example of a one-bit sliding window protocol that uses acknowledgments to control the window.
The transport layer provides efficient, reliable, and cost-effective process-to-process delivery by making use of network layer services. The transport layer works through transport entities to achieve its goal of reliable delivery between application processes. It provides an interface for applications to access its services.
Network devices like hubs, switches, and routers connect computers in a network and help manage traffic flow. Hubs broadcast all received data to all ports but have limited bandwidth. Switches can connect more devices than hubs and have features like VLANs. Routers connect different networks and use IP addresses to direct traffic. Other devices like firewalls, VPNs, and IDS/IPS provide network security functions.
Proactive routing protocol
Each node maintain a routing table.
Sequence number is used to update the topology information
Update can be done based on event driven or periodic
Observations
May be energy expensive due to high mobility of the nodes
Delay can be minimized, as path to destination is already known to all nodes.
The document discusses the differences between packets and frames, and provides details on the transport layer. It explains that the transport layer is responsible for process-to-process delivery and uses port numbers for addressing. Connection-oriented protocols like TCP use three-way handshaking for connection establishment and termination, and implement flow and error control using mechanisms like sliding windows. Connectionless protocols like UDP are simpler but unreliable, treating each packet independently.
This document summarizes key topics related to data link control and protocols. It discusses framing methods like fixed-size and variable-size framing. It also covers flow control, error control, and protocols for both noiseless and noisy channels. Specific protocols described include the Simplest Protocol, Stop-and-Wait Protocol, Stop-and-Wait ARQ, Go-Back-N ARQ, and Selective Repeat ARQ. The document provides details on their design, algorithms, and flow diagrams to illustrate how each protocol handles framing, flow control, and error control.
IP specifies the format of packets and an addressing scheme to allow communication between devices on a network. While IP alone only supports one-way transmission like a postal system, TCP/IP establishes two-way connections between hosts to allow them to send messages back and forth. IP addresses are unique identifiers for network interfaces, consisting of a network prefix and host number. IP addresses are divided into classes A-E based on their format and usage. Subnetting allows networks to be divided into smaller subnetworks to better utilize blocks of addresses.
Static channel allocation uses time division multiplexing and frequency division multiplexing to allocate channels to users. Each user is statically assigned a specific portion of the frequency spectrum or time slot. This method is inefficient because it wastes bandwidth if the number of users is less than the number of portions the spectrum is divided into. It also causes delays for new users who need to wait for channels to become available before using the resource.
This document provides an overview of various application layer protocols including electronic mail (SMTP, POP3, IMAP), HTTP, web services, DNS, and SNMP. It discusses the distinction between application programs and protocols, how protocols implement remote procedure calls, and that protocols have companion protocols that define message formats. Specific protocols covered in more detail include SMTP for mail transfer, POP3 and IMAP for mail access, HTTP for web access, and the general functions of DNS and SNMP in networks.
Congestion avoidance mechanisms aim to predict impending congestion and reduce data transmission rates before packet loss occurs. Three main methods are DEC bit, Random Early Detection (RED), and source-based approaches. DEC bit uses routers to explicitly notify sources of congestion. RED drops packets probabilistically based on average queue length to implicitly notify sources. Source-based methods monitor round-trip times and window sizes to detect congestion and adjust transmission rates accordingly.
The transport layer provides end-to-end communication over a network by providing services such as connection-oriented communication, reliability, flow control, and multiplexing. It links the application layer to the network layer and performs functions like segmenting messages and establishing connections between endpoints. Common transport protocols are TCP, which provides connection-oriented and reliable data transfer, and UDP, which provides connectionless datagram delivery.
Quality of service aims to provide different levels of priority to different applications, users, or data flows. It is achieved through techniques like scheduling, traffic shaping, resource reservation, and admission control. Scheduling methods include FIFO queuing, priority queuing, and weighted fair queuing. Traffic shaping uses leaky bucket and token bucket algorithms. Resource reservation reserves buffer space, bandwidth, and other resources beforehand. Admission control restricts packet admission based on specifications. Models for QoS include the Integrated Services Model, which requires resource reservation in advance using RSVP, and the Differentiated Services Model, which differentiates traffic into classes.
Link state routing protocols work by having each node independently construct a map of the network connectivity and calculate the best path to every destination. Each node sends link state advertisements containing its connections to all other nodes. As these advertisements are flooded through the network, each node builds an identical map and independently calculates the shortest paths using an algorithm like Dijkstra's. The routing table is then filled in based on the first node along the shortest path from the root node to each destination in the shortest path tree.
The document discusses the evolution of Ethernet standards over four generations from its creation in 1976. It describes the IEEE 802 project which established standards for LAN communication. The original Ethernet standard defined the data link layer to consist of logical link control (LLC) and media access control (MAC) sublayers. It also established physical layer standards and frame formats for early Ethernet implementations using thick and thin coaxial cable and twisted pair wiring in bus and star topologies. Later changes like bridging and switching increased bandwidth and separated collision domains to support higher data rates.
The network layer provides two main services: connectionless and connection-oriented. Connectionless service routes packets independently through routers using destination addresses and routing tables. Connection-oriented service establishes a virtual circuit between source and destination, routing all related traffic along the pre-determined path. The document also discusses store-and-forward packet switching, where packets are stored until fully received before being forwarded, and services provided to the transport layer like uniform addressing.
The document provides an overview of different routing algorithms:
- It describes shortest path routing and discusses properties like optimality, simplicity, and robustness that routing algorithms should have.
- Common routing algorithms are described briefly, including flooding, distance vector routing, link state routing, and hierarchical routing.
- Specific routing algorithms like Dijkstra's algorithm, flow based routing, and link state routing are explained in more detail through examples.
- Issues with distance vector routing like the count to infinity problem are also covered.
- The talk concludes with hierarchical routing being presented as a solution for scaling routing to larger networks.
There are two types of network links: point-to-point links between two nodes and broadcast links where nodes share a common transmission medium. Broadcast links use multiple access protocols to determine how nodes access the shared medium as only one node can transmit at a time. Common multiple access protocols for broadcast links include Aloha, CSMA, and CSMA/CD which use random access or carrier sensing to regulate transmissions and avoid or detect collisions between nodes transmitting simultaneously. Controlled access protocols like token passing also exist where nodes must obtain a token to transmit on the shared medium.
The document discusses data link layer protocols, including LLC, MAC, and Ethernet standards. It describes the functions of the physical layer, data link layer, and logical link control sublayer. It also covers IP addressing schemes like IPv4 addresses, network classes, public vs private addresses, and subnetting. CIDR is introduced as a method to improve address space utilization and routing scalability on the internet.
Mobile transport layer - traditional TCPVishal Tandel
This document summarizes several mechanisms proposed to improve TCP performance in wireless networks. It discusses approaches like indirect TCP, snooping TCP, and mobile TCP that split the TCP connection to isolate the wireless link. It also covers fast retransmit/recovery techniques, transmission freezing, and selective retransmission to more efficiently handle packet losses due to mobility. While each approach aims to address TCP issues in wireless networks, they often do so by mixing layers or requiring changes to the basic TCP protocol stack.
The document discusses network models including the OSI model and TCP/IP protocol suite. The OSI model has 7 layers - physical, data link, network, transport, session, presentation, and application layers. Each layer has a specific function in communication. Similarly, the TCP/IP protocol suite has 5 layers that correspond to the OSI layers - physical, data link, network, transport, and application. The document also discusses different types of addresses used in networking including physical, logical, port, and specific addresses.
SOLUTION MANUAL OF COMMUNICATION NETWORKS BY ALBERTO LEON GARCIA & INDRA WIDJAJAvtunotesbysree
The document provides solutions to chapter 1 problems from the textbook "Communication Networks" by Alberto Leon Garcia and Indra Widjaja.
The solutions describe the procedures involved in mailing a letter and sending an email. They are both connectionless services. Procedures for making a telephone call and providing personal communication services are also described. Setting up telephone calls is connection-oriented. Requirements for interactive online games over connection-oriented and connectionless networks are discussed. Networks must support real-time delivery of commands and responses for interactive games and applications.
The document provides an overview of the transport layer in computer networks. It discusses the key services provided by the transport layer, including reliable data transmission and isolating applications from the underlying network technology. It introduces some common transport layer protocols like TCP and UDP, and describes important transport layer concepts such as connection-oriented vs. connectionless services, transport service primitives, and elements that transport protocols must address like error control and flow control.
The document discusses delivery, forwarding, and routing in computer networks. It defines delivery as handling packets by underlying physical networks based on supervision from the network and data link layers. Forwarding is placing a packet in its route to the destination by using a routing table. Routing refers to how routing tables are created to help with forwarding. Common routing protocols discussed include distance-vector protocols like RIP and IGRP, link-state protocols like OSPF and IS-IS, and BGP for routing between autonomous systems.
The document discusses network layer delivery, forwarding, and routing. It covers topics such as direct versus indirect delivery, forwarding techniques including routing tables and processes, unicast routing protocols including intra-domain and inter-domain routing as well as distance vector, link state, and path vector routing protocols. It also discusses multicast routing protocols. Key concepts are explained through examples and figures.
The document discusses the differences between packets and frames, and provides details on the transport layer. It explains that the transport layer is responsible for process-to-process delivery and uses port numbers for addressing. Connection-oriented protocols like TCP use three-way handshaking for connection establishment and termination, and implement flow and error control using mechanisms like sliding windows. Connectionless protocols like UDP are simpler but unreliable, treating each packet independently.
This document summarizes key topics related to data link control and protocols. It discusses framing methods like fixed-size and variable-size framing. It also covers flow control, error control, and protocols for both noiseless and noisy channels. Specific protocols described include the Simplest Protocol, Stop-and-Wait Protocol, Stop-and-Wait ARQ, Go-Back-N ARQ, and Selective Repeat ARQ. The document provides details on their design, algorithms, and flow diagrams to illustrate how each protocol handles framing, flow control, and error control.
IP specifies the format of packets and an addressing scheme to allow communication between devices on a network. While IP alone only supports one-way transmission like a postal system, TCP/IP establishes two-way connections between hosts to allow them to send messages back and forth. IP addresses are unique identifiers for network interfaces, consisting of a network prefix and host number. IP addresses are divided into classes A-E based on their format and usage. Subnetting allows networks to be divided into smaller subnetworks to better utilize blocks of addresses.
Static channel allocation uses time division multiplexing and frequency division multiplexing to allocate channels to users. Each user is statically assigned a specific portion of the frequency spectrum or time slot. This method is inefficient because it wastes bandwidth if the number of users is less than the number of portions the spectrum is divided into. It also causes delays for new users who need to wait for channels to become available before using the resource.
This document provides an overview of various application layer protocols including electronic mail (SMTP, POP3, IMAP), HTTP, web services, DNS, and SNMP. It discusses the distinction between application programs and protocols, how protocols implement remote procedure calls, and that protocols have companion protocols that define message formats. Specific protocols covered in more detail include SMTP for mail transfer, POP3 and IMAP for mail access, HTTP for web access, and the general functions of DNS and SNMP in networks.
Congestion avoidance mechanisms aim to predict impending congestion and reduce data transmission rates before packet loss occurs. Three main methods are DEC bit, Random Early Detection (RED), and source-based approaches. DEC bit uses routers to explicitly notify sources of congestion. RED drops packets probabilistically based on average queue length to implicitly notify sources. Source-based methods monitor round-trip times and window sizes to detect congestion and adjust transmission rates accordingly.
The transport layer provides end-to-end communication over a network by providing services such as connection-oriented communication, reliability, flow control, and multiplexing. It links the application layer to the network layer and performs functions like segmenting messages and establishing connections between endpoints. Common transport protocols are TCP, which provides connection-oriented and reliable data transfer, and UDP, which provides connectionless datagram delivery.
Quality of service aims to provide different levels of priority to different applications, users, or data flows. It is achieved through techniques like scheduling, traffic shaping, resource reservation, and admission control. Scheduling methods include FIFO queuing, priority queuing, and weighted fair queuing. Traffic shaping uses leaky bucket and token bucket algorithms. Resource reservation reserves buffer space, bandwidth, and other resources beforehand. Admission control restricts packet admission based on specifications. Models for QoS include the Integrated Services Model, which requires resource reservation in advance using RSVP, and the Differentiated Services Model, which differentiates traffic into classes.
Link state routing protocols work by having each node independently construct a map of the network connectivity and calculate the best path to every destination. Each node sends link state advertisements containing its connections to all other nodes. As these advertisements are flooded through the network, each node builds an identical map and independently calculates the shortest paths using an algorithm like Dijkstra's. The routing table is then filled in based on the first node along the shortest path from the root node to each destination in the shortest path tree.
The document discusses the evolution of Ethernet standards over four generations from its creation in 1976. It describes the IEEE 802 project which established standards for LAN communication. The original Ethernet standard defined the data link layer to consist of logical link control (LLC) and media access control (MAC) sublayers. It also established physical layer standards and frame formats for early Ethernet implementations using thick and thin coaxial cable and twisted pair wiring in bus and star topologies. Later changes like bridging and switching increased bandwidth and separated collision domains to support higher data rates.
The network layer provides two main services: connectionless and connection-oriented. Connectionless service routes packets independently through routers using destination addresses and routing tables. Connection-oriented service establishes a virtual circuit between source and destination, routing all related traffic along the pre-determined path. The document also discusses store-and-forward packet switching, where packets are stored until fully received before being forwarded, and services provided to the transport layer like uniform addressing.
The document provides an overview of different routing algorithms:
- It describes shortest path routing and discusses properties like optimality, simplicity, and robustness that routing algorithms should have.
- Common routing algorithms are described briefly, including flooding, distance vector routing, link state routing, and hierarchical routing.
- Specific routing algorithms like Dijkstra's algorithm, flow based routing, and link state routing are explained in more detail through examples.
- Issues with distance vector routing like the count to infinity problem are also covered.
- The talk concludes with hierarchical routing being presented as a solution for scaling routing to larger networks.
There are two types of network links: point-to-point links between two nodes and broadcast links where nodes share a common transmission medium. Broadcast links use multiple access protocols to determine how nodes access the shared medium as only one node can transmit at a time. Common multiple access protocols for broadcast links include Aloha, CSMA, and CSMA/CD which use random access or carrier sensing to regulate transmissions and avoid or detect collisions between nodes transmitting simultaneously. Controlled access protocols like token passing also exist where nodes must obtain a token to transmit on the shared medium.
The document discusses data link layer protocols, including LLC, MAC, and Ethernet standards. It describes the functions of the physical layer, data link layer, and logical link control sublayer. It also covers IP addressing schemes like IPv4 addresses, network classes, public vs private addresses, and subnetting. CIDR is introduced as a method to improve address space utilization and routing scalability on the internet.
Mobile transport layer - traditional TCPVishal Tandel
This document summarizes several mechanisms proposed to improve TCP performance in wireless networks. It discusses approaches like indirect TCP, snooping TCP, and mobile TCP that split the TCP connection to isolate the wireless link. It also covers fast retransmit/recovery techniques, transmission freezing, and selective retransmission to more efficiently handle packet losses due to mobility. While each approach aims to address TCP issues in wireless networks, they often do so by mixing layers or requiring changes to the basic TCP protocol stack.
The document discusses network models including the OSI model and TCP/IP protocol suite. The OSI model has 7 layers - physical, data link, network, transport, session, presentation, and application layers. Each layer has a specific function in communication. Similarly, the TCP/IP protocol suite has 5 layers that correspond to the OSI layers - physical, data link, network, transport, and application. The document also discusses different types of addresses used in networking including physical, logical, port, and specific addresses.
SOLUTION MANUAL OF COMMUNICATION NETWORKS BY ALBERTO LEON GARCIA & INDRA WIDJAJAvtunotesbysree
The document provides solutions to chapter 1 problems from the textbook "Communication Networks" by Alberto Leon Garcia and Indra Widjaja.
The solutions describe the procedures involved in mailing a letter and sending an email. They are both connectionless services. Procedures for making a telephone call and providing personal communication services are also described. Setting up telephone calls is connection-oriented. Requirements for interactive online games over connection-oriented and connectionless networks are discussed. Networks must support real-time delivery of commands and responses for interactive games and applications.
The document provides an overview of the transport layer in computer networks. It discusses the key services provided by the transport layer, including reliable data transmission and isolating applications from the underlying network technology. It introduces some common transport layer protocols like TCP and UDP, and describes important transport layer concepts such as connection-oriented vs. connectionless services, transport service primitives, and elements that transport protocols must address like error control and flow control.
The document discusses delivery, forwarding, and routing in computer networks. It defines delivery as handling packets by underlying physical networks based on supervision from the network and data link layers. Forwarding is placing a packet in its route to the destination by using a routing table. Routing refers to how routing tables are created to help with forwarding. Common routing protocols discussed include distance-vector protocols like RIP and IGRP, link-state protocols like OSPF and IS-IS, and BGP for routing between autonomous systems.
The document discusses network layer delivery, forwarding, and routing. It covers topics such as direct versus indirect delivery, forwarding techniques including routing tables and processes, unicast routing protocols including intra-domain and inter-domain routing as well as distance vector, link state, and path vector routing protocols. It also discusses multicast routing protocols. Key concepts are explained through examples and figures.
The document provides an overview of network layer concepts including delivery, forwarding, routing, and routing protocols. It discusses direct vs indirect delivery, forwarding techniques and routing tables, unicast routing protocols like RIP, OSPF, BGP, and multicast routing protocols. Key topics covered include delivery, forwarding, routing tables, distance vector routing, link state routing, path vector routing, multicast applications, multicast routing approaches, and protocols like PIM-DM and PIM-SM. Figures and examples illustrate related concepts.
The document provides an overview of network layer concepts including delivery, forwarding, routing, and routing protocols. It discusses direct vs indirect delivery, forwarding techniques and routing tables, unicast routing protocols like RIP, OSPF, BGP, and multicast routing protocols. Key topics covered include delivery, forwarding, routing tables, distance vector routing, link state routing, path vector routing, multicast applications, multicast routing approaches, and protocols like PIM-DM and PIM-SM. Figures and examples illustrate related concepts.
1) The document discusses different methods for IP address assignment including manual configuration, RARP, BOOTP, and DHCP. It then describes each method in more detail, focusing on RARP, BOOTP, and DHCP.
2) Routing protocols like RIP, OSPF, and BGP are covered along with the differences between interior routing protocols within an autonomous system and exterior routing protocols between autonomous systems. Distance vector and link state routing algorithms are also introduced.
3) Dynamic routing allows routing tables to be automatically updated when the network changes, while static routing requires manual configuration changes. Interior gateway protocols operate within an autonomous system while exterior gateway protocols route between autonomous systems.
Network layer ip address assignment and routingHamzahMohammed4
1) The document discusses different methods for IP address assignment including manual configuration, RARP, BOOTP, and DHCP. It then describes each method.
2) RARP allows diskless workstations to obtain their IP address from a RARP server by broadcasting a request message during bootup. The server responds with the client's IP to MAC address mapping.
3) BOOTP and DHCP both allow clients to broadcast a request for an IP address, with DHCP providing additional configuration options and the ability for servers to dynamically assign addresses.
Routing is the process of moving information across an internetwork from a source to a destination. There are two types of routing: direct delivery where the source and destination are on the same network, and indirect delivery where packets travel through multiple routers to reach the destination on a different network. Distance vector routing protocols like RIP use hop count as the metric and periodically share routing tables with neighboring routers to allow all routers to learn the optimal paths. However, this can cause instability issues like two-node and three-node loops where routers incorrectly update their routing tables.
This document contains questions and answers related to CCNA 1 Chapter 5. It includes 21 multiple choice questions about networking concepts like routing, default gateways, broadcast domains, and dynamic versus static routing. It also provides explanations and examples related to using network addresses to forward packets between different interfaces and networks.
VLSM allows a network administrator to utilize multiple subnet masks in the same IP address space. A /29 mask must be used to create eight smaller subnetworks from a /28 subnet, each having two usable host addresses. The most efficient route summary that can be configured on Router3 to advertise the internal networks to the cloud is 192.1.1.0/23 and 192.1.1.64/23.
The document contains sample questions and answers from a CCNA 2 Chapter 2 exam. It lists multiple choice questions about static routing concepts like administrative distance, route summarization, next hop addresses, and troubleshooting routing issues. It also includes exhibits of network diagrams and configuration outputs to aid in understanding the routing scenarios described in each question.
This document provides an overview of network layer concepts including delivery, forwarding, routing, and routing protocols. It discusses direct vs indirect delivery and how forwarding requires routers and hosts to have routing tables to determine the next hop for packet delivery. Distance vector and link state routing protocols are covered as well as intra- and inter-domain routing. Multicast routing is also introduced, covering applications, unicast vs multicast, and common multicast routing protocols. Numerous diagrams and examples are provided to illustrate key networking concepts.
This document discusses internet routing and forwarding techniques. It explains how IP packets are routed from one sub-network to another using routers. It describes different forwarding techniques including next-hop, network-specific, host-specific, and default methods. It also discusses forwarding with classful and classless addressing as well as concepts like address aggregation, hierarchical routing, and geographical routing that help reduce routing table sizes.
The document appears to be a practice exam for the CCNA 3 Switching Basics and Intermediate Routing certification. It contains 20 multiple choice questions covering topics like RIP routing protocol versions 1 and 2, VLSM, route summarization, and limitations of RIP v1. The questions test knowledge of subnetting, classful and classless routing concepts, and configuration of routing protocols.
VLSM allows a network administrator to utilize multiple subnet masks in the same IP address space. A /29 mask must be used to create eight smaller subnetworks from a /28 subnet, with each having two usable host addresses. The most efficient route summary that can be configured on Router3 to advertise the internal networks to the cloud is 192.1.1.0/23 and 192.1.1.64/23.
This document summarizes the routing table lookup process used by routers to determine the best route to forward IP packets. It begins by explaining the basic steps of the process, including finding a matching network route, determining if it is an ultimate or parent route, and checking for more specific subnet routes. It then provides examples to illustrate what constitutes a match between the destination IP address and routes in the routing table. The key points are that the subnet mask specifies the minimum number of bits that must match, and the route with the longest bit match is selected. The document uses a sample network configuration to demonstrate how the process works in practice when evaluating parent and child routes.
Two functions of a router are:
1. It forwards data packets toward their destination.
2. It acts as an intersection between multiple IP networks.
The likely cause of the problem on R3 is that the configuration register is not configured with the default setting.
Flash memory contains a scaled-down version of the IOS that can be used to reload a complete version of the IOS in the event that the IOS becomes damaged or corrupted.
The document discusses routing protocols used in internets and autonomous systems. It describes how distance vector routing protocols like RIP work by sharing routing tables between neighbors. It also explains link state routing protocols like OSPF, where each router shares information about connected links and all routers can independently calculate optimal routes. Finally, it outlines path vector routing and BGP, which is used for inter-domain routing between autonomous systems and considers routing policies.
This document discusses distance vector routing protocols. It provides an example of distance vector routing with 5 routers connected by 6 links. Initially, each router only knows about directly connected networks. Routers periodically exchange routing tables, allowing each to learn paths to all networks. After a few iterations, the routing tables converge with each router having an optimal path to every network. Distance vector protocols work by routers broadcasting their routing tables to neighbors and updating paths based on received distances.
Cisco discovery drs ent module 6 - v.4 in english.igede tirtanata
The document contains multiple choice questions about OSPF routing. It tests knowledge of OSPF concepts like DR/BDR election, network types, route calculation, and configuration. The questions cover topics such as OSPF network statements, adjacency formation between routers, and using OSPF in different network types.
- A static route is established with the command "ip route 192.168.2.0 255.255.255.0 S0/0/0" on router R1. This establishes a static route and forwards traffic for the 192.168.2.0 network to the next hop S0/0/0.
- The static route is not automatically propagated. It needs to be manually configured on any other routers to establish the path between the two networks.
- Static routes are generally not preferred over dynamic routing protocols but can provide a quick solution until dynamic routing is configured.
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Introduction to AI for Nonprofits with Tapp NetworkTechSoup
Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
MATATAG CURRICULUM: ASSESSING THE READINESS OF ELEM. PUBLIC SCHOOL TEACHERS I...NelTorrente
In this research, it concludes that while the readiness of teachers in Caloocan City to implement the MATATAG Curriculum is generally positive, targeted efforts in professional development, resource distribution, support networks, and comprehensive preparation can address the existing gaps and ensure successful curriculum implementation.
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
it describes the bony anatomy including the femoral head , acetabulum, labrum . also discusses the capsule , ligaments . muscle that act on the hip joint and the range of motion are outlined. factors affecting hip joint stability and weight transmission through the joint are summarized.
How to Fix the Import Error in the Odoo 17Celine George
An import error occurs when a program fails to import a module or library, disrupting its execution. In languages like Python, this issue arises when the specified module cannot be found or accessed, hindering the program's functionality. Resolving import errors is crucial for maintaining smooth software operation and uninterrupted development processes.
This slide is special for master students (MIBS & MIFB) in UUM. Also useful for readers who are interested in the topic of contemporary Islamic banking.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
Objective:
Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
2. 2
Network Layer II (routing)
Routing Styles:
Static vs. Dynamic Routing
Routing Protocols/Algorithms
Routing Table
Routing Information Protocol (RIP) & Distance Vector Routing
(DVR)
Open Shortest Path First (OSPF) & Link State Routing (LSR)
Dijkstra’s “Shortest Path” Algorithm
Border Gateway Protocol (BGP) and Path Vector Routing (PVR)
3. Routing Protocol & Routing Algorithm
3
A Routing Protocol is a combination of rules and
procedures that lets routers in an internet inform
each other of changes. It allows routers to share
whatever they know about the internet or their
neighbourhood.
A Routing Algorithm is that part of network
layer software responsible fro deciding which
output line and incoming packet should be
transmitted on.
4. 4
Routing
a) Routing requires a host or a router to have a routing table.
b) Usually when a host has a packet to send or when a router has
received a packet to be forwarded, it looks at this table to find the
route to the final destination.
c) However, this simple solution is impossible in today’s Internet
world because the number of entries in the routing table makes the
table lookups inefficient.
d) Need to make the size of table manageable and handles issues such
security at the same time. The key question is how to design the
routing table.
e) Next-hop routing, Network-specific routing, host specific routing
f) Static versus Dynamic Routing
g) Routing Protocols: RIP, OSPF, BGP
h) Routing Algorithms: DVR, LSR, PVR
6. 6
Network-specific & host-specific routing
Instead of having an entry for every host
connected to the same network, only one entry
is needed to defined the address of the network
itself. All host connected to the same network
as one single entity.
The destination host address
is given in the routing table;
to have greater control over
routing.
7. 7
Default routing
R1 is used to route packets to hosts
connected to N2.
However, R2 is used to as default to
route other packets to the rest of
Internet without listing all the
networks involved
Only one default routing is allowed
with network address 0.0.0.0
8. 8
General Routing Table
Flags
U The router is up and running.
G The destination is in another network.
H Host-specific address.
D Added by redirection.
M Modified by redirection.
9. 9
Routing table
a) Generally, a routing table needs a minimum of 4
columns: mask, destination network address, next hop
address and interface.
b)When a packet arrives, the router applies the mask to the
destination address it receives (one-by-one until a match
is found) in order to find the corresponding destination
network address.
c) So, the mask serves as essential tool to match destination
address in routing table and the address it receives.
d)If found, the packet is sent out from the corresponding
interface in the table. If not found, the packet is delivered
to the default interface which carries the packet to
default router.
10. 10
Configuration for routing example
Mask Dest. Next Hop I.
255.0.0.0 111.0.0.0 -- m0
255.255.255.224 193.14.5.160 - m2
255.255.255.224 193.14.5.192 - m1
255.255.255.255 194.17.21.16 111.20.18.14 m0
255.255.255.0 192.16.7.0 111.15.17.32 m0
255.255.255.0 194.17.21.0 111.20.18.14 m0
0.0.0.0 0.0.0.0 111.30.31.18 m0
Standard
delivery
Host-specific
Network-
specific
Default
11. 11
Example 1Example 1
Router R1 receives 500 packets for destination 192.16.7.14; the
algorithm applies the masks row by row to the destination address
until a match (with the value in the second column of Dest. in
table) is found:
SolutionSolution
Direct delivery
192.16.7.14 & 255.0.0.0 192.0.0.0 no match to 111.0.0.0
192.16.7.14 & 255.255.255.224 192.16.7.0 no match to 193.14.5.160
192.16.7.14 & 255.255.255.224 192.16.7.0 no match to 193.14.5.192
Host-specific
192.16.7.14 & 255.255.255.255 192.16.7.14 no match to 194.17.21.16
Network-specific
192.16.7.14 & 255.255.255.0 192.16.7.0 match to 192.16.7.0
Rule of thumb: Apply the individual mask (from Routing
table) to the received destination address (row-by-row)
and see if its matches any of the DEST address stated in
its routing table. If match is found, then stop
12. 12
Example 2Example 2
Router R1 receives 100 packets for destination 193.14.5.176; the
algorithm applies the masks row by row to the destination address
until a match is found:
SolutionSolution
Direct delivery
193.14.5.176 & 255.0.0.0 193.0.0.0 no match
193.14.5.176 & 255.255.255.224 193.14.5.160 match
13. 13
Example 3Example 3
Router R1 receives 20 packets for destination 200.34.12.34; the
algorithm applies the masks row by row to the destination address
until a match is found:
SolutionSolution
200.34.12.34 & 255.0.0.0 200.0.0.0 no match
200.34.12.34 & 255.255.255.224 200.34.12.32 no match
200.34.12.34 & 255.255.255.224 200.34.12.32 no match
200.34.12.34 & 255.255.255.255 200.34.12.34 no match
200.34.12.34 & 255.255.255.0 200.34.12.0 no match
200.34.12.34 & 255.255.255.0 200.34.12.0 no match
Default
200.34.12.34 & 0.0.0.0 0.0.0.0. match
14. 14
Example 4Example 4 Make the routing table for router R1 in figure below
SolutionSolution
Mask Destination Next Hop I.
255.255.0.0 134.18.0.0 -- m0
255.255.0.0 129.8.0.0 222.13.16.40 m1
255.255.255.0 220.3.6.0 222.13.16.40 m1
0.0.0.0 0.0.0.0 134.18.5.2 m0
15. 15
Example 5Example 5 Make the routing table for router R1 in figure below
Subnet mask Destination Next Hop
I.
255.255.255.0 200.8.4.0 ---- m2
255.255.255.0 80.4.5.0 201.4.10.3 m1
or 200.8.4.12 or m2
255.255.255.0 80.4.6.0 201.4.10.3 m1
or 200.4.8.12 or m2
0.0.0.0 0.0.0.0 m0
SolutionSolution
17. 17
Routing Tables in IP with CIDR
(Classless InterDomain Routing)
Mask Destination Next Hop
/12 128.96.0.0 145.12.56.29
/17 128.125.0.0 153.202.12.128
/12 128.112.0.0 153.202.14.1
/26 128.105.14.64 153.2.45.101
/32 128.105.14.66 153.2.45.101
For each entry in the routing table:
MaskedAddress := EntryMask (bitAND) IPDatagramDestinationAddress;
if (MaskedAddress == EntryDestination)
Mark the entry;
Choose the marked entry with the longest Mask prefix.
18. 18
Make a routing table for router R1, using the
configuration in Figure belowExample 7aExample 7a
Routing table for router R1 in Figure aboveSolutionSolution
m3
The table is sorted from the longest mask to the shortest mask.
19. 19
Show the forwarding process if a packet arrives at
R1 with the destination address 180.70.65.140.
The router performs the following steps:
1. The first mask (/26) is applied to the destination address.
The result is 180.70.65.128, which does not match the
corresponding network address.
2. The second mask (/25) is applied to the destination
address. The result is 180.70.65.128, which matches the
corresponding network address. The next-hop address
and the interface number m0 are passed on for
further processing.
Example 7bExample 7b
SolutionSolution
20. 20
Show the forwarding process if a packet arrives at
R1 with the destination address 201.4.22.35.
The router performs the following steps:
1. The first mask (/26) is applied to the destination address. The
result is 201.4.22.0, which does not match the corresponding
network address.
2. The second mask (/25) is applied to the destination address. The
result is 201.4.22.0, which does not match the corresponding
network address (row 2).
Example 7cExample 7c
SolutionSolution
3. The third mask (/24) is applied to the destination address. The
result is 201.4.22.0, which matches the corresponding network
address..
21. 21
Show the forwarding process if a packet arrives at
R1 with the destination address 18.24.32.78.
This time all masks are applied, one by one, to the destination
address, but no matching network address is found. When it reaches
the end of the table, the module gives the default next-hop address
180.70.65.200 (because it could not find the match) . This is
probably an outgoing package that needs to be sent, via the default
router, to someplace else in the Internet.
Example 7dExample 7d
SolutionSolution
22. 22
Routing/routers
a) An internet is a combination of networks connected by routers.
b) When a packet goes from a source to a destination, it will pass
through many routers until it reaches the router attached to
destination network.
c) A router consults a routing table when a packet is ready to be
forwarded. The routing table specifies the optimum path for the
packet and can be either static of dynamic. Dynamic routing is more
popular.
d) Static table does not change frequently. Dynamic table is updated
automatically when there is a change somewhere in the network; i.e
when a route is down or a better route has been created.
e) Routing protocols is a combination of rules/procedures that lets
routers in the internet inform one another when changes occur;
mostly based on sharing/combining information between routers at
different networks.
23. 23
Unicast Routing
a) Unicast = one source and one destination. (1-to-1 relationship).
b) In Unicast routing, when a router receives a packet, it forwards the
packet thru only one of its ports as defined in the routing table. The
router may discard the packet if it cannot find the destination
address
c) Questions: In dynamic routing, how does the router decides to
which network should it pass the packet next? What routing
algorithm is the routing based on? The decision is based on
optimisation: which of the available pathways is the best/optimum
path?
d) But how to measure? A metric is a cost assigned for passing thru a
network and the total metric of a particular route is equal to the sum
of the metrics of networks that comprise the route.
e) Simple protocols such as Routing Information Protocol (RIP), treat
all network equally; cost of passing each network is the same as one
hop count per network.
25. 25
Routing Architecture in the Internet
Fact:
Nobody owns the whole Internet.
However, parts of the Internet are owned and administered by
commercial and public organisations (such as ISPs, universities,
governmental offices, research institutes, companies etc.).
Idea:
Divide the Internet in Autonomous Systems (AS) that are
independently administered by individual organisations. Let each
administrative authority use its own routing protocol within the
AS. Let’s use one routing protocol to exchange routing
information among AS.
26. 26
Routing Architecture in the Internet
An AS is a group of networks and routers under the authority
of a single administrator.
27. 27
A static routing table
contains information entered manually
Usually remained unchanged.
A dynamic routing table is updated
periodically or whenever necessarily
using one of the dynamic routing protocols
such as RIP, OSPF, or BGP.
Static versus Dynamic RoutingStatic versus Dynamic Routing
28. 28
Routing Protocols: Interior vs Exterior
• Routing inside an AS is referred to as interior routing whereas routing between ASs
is referred to as exterior routing.
• Each AS can choose one or more interior routing protocols inside an AS.
• Only one exterior routing protocol is usually chosen to handle routing between
ASs.
• To know the next ’path’ (or router) a packet should be pass-on, the decision is
based on some optimisation rule/protocol, e.g. using different assignment of the cost
30. 30
Distance Vector Routing (DVR)
a) 3 keys to understand how this algorithm works:
• Sharing knowledge about the entire AS. Each router
shares its knowledge about the entire AS with
neighbours. It sends whatever it has.
• Sharing only with immediate neighbours. Each
router sends whatever knowledge it has thru all its
interface.
• Sharing at regular intervals. sends at fixed intervals,
e.g. every 30 sec.
a) Problems: Tedious comparing/updating process, slow
response to infinite loop problem, huge list to be
maintained!!
32. 32
Updating in distance vector routing example: C to A
A to A via C: ACA = AC+ CA = 2+2
A to B via C: ACB = AC + CB = 2+4
From C From A
A to D via C: ACD = AC + CD = 2+ inf.
A to C via C: ACB = AC + CC = 2+0
A to E via C: ACD = AC + CE = 2+4
34. 34
DVR example from Tenenbaum (with estimated delay given
slightly different)
(a) A subnet. (b) Input from A, I, H, K, and the new routing table for J.
1st
DRAWBACK: VERY SLOW!!!
Each router maintain a table (a vector)
giving the best known metric (or
delay) to each destination and which
line to use. These tables are then
updated by exchanging information
with the neighbours (direct link, 1 hop)
JA,8
JB, JAB, 8+12
JC, JIC, 10+18
JD, JHD, 12+8
JE, JIE. 10+7
JF, JIF, 10+20
JG, JHG, 12+6
JH, 12
JI. 10
JJ, 0
JK, 6
JL, JKL, 6+9
Neighbour routers
35. 35
Routing Information Protocol (RIP)
a) RIP is based on distance vector routing, which uses the Bellman-
Ford algorithm for calculating the routing table.
b) RIP treats all network equals; the cost of passing thru a network
is the same: one hop count per network.
c) Each router/node maintains a vector (table) of minimum
distances to every node. (the least-cost route btw any nodes is the
route with the minimum number of hop-count).
d) The hop-count is the number of networks that a packet
encounters to reach its destination. Path costs are based on
number of hops.
e) In distance vector routing, each router periodically shares its
knowledge about the entire internet with its neighbour.
f) Each router keeps a routing table that has one entry for each
destination network of which the router is aware.
g) The entry consists of Destination Network Address/id, Hop-
Count and Next-Router.
40. 40
Infinite loop problem in DVR
The count-to-infinity problem!
Good news (a) travels faster than bad news (b)
React rapidly to good news but slowly to bad news
Although it will eventual converge to correct answer, they adapt slowly,
they must be told to change. Convergence to the correct answer is slow.
A initially down; hence A initially up then down
42. 42
Open Shortest Path First (OSPF)
a) OSPF uses link state routing to update the routing table in an area;
OSPF divides an AS into different areas (depending on their
type).
b) Unlike RIP, OSPF treats the entire network within differently with
different philosophy; depending on the types, cost (metric) and
condition of each link: to define the ‘state’ of a link.
c) OSPF allows the administrator to (only) assign a cost for passing
through a network based on the type of service required. e.g.
minimum delay, maximum throughput. (but not stating exact path)
d) Each router should have the exact topology of the AS network(a
picture of entire AS network) at every moment. The topology is a
graph consisting of nodes and edges.
e) Each router needs to advertise to the neighbourhood of every
other routers involved in an Area. (flood)
43. 43
Areas in an Autonomous System
Open Shortest Path First (OSPF)
OSPF divides an AS into areas. An area is a collection of network, hosts and routers
all contained within an AS. Routers inside an area flood the area with routing info. At
the border of an Area, special routers called Area Border routers summarize the
info. about the area and send it to other area. Among the areas inside an AS is a
special area called the Backbone connecting all areas through Backbone routers and
serves as a primary area to the outside (other ASs) via the AS Boundary router.
(AS>Areas)
44. 44
Link State Routing (LSR)
a) Like RIP, in link state routing, each router also shares its knowledge
about its neighbourhood with every routers in the area.
b) However, in LSR, the link-state packet (LSP) defines the best known
network topology (of an area) is sent to every routers (of other area)
after it is constructed locally. Whereas RIP slowly converge to final
routing list based information received from immediate neighbours.
c) 3 keys to understand how this algorithm works:
• Sharing knowledge about the neighbourhood. Each router sends the state of
its neighbourhood to every other router in the area.
• Sharing with every other routers. Thru process of flooding. each router sends
the state of its neighbourhood thr all its output ports and each neighbour sends
to every other neighbours and so on until all routers received same full
information eventually.
• Sharing when there is a change. Each router share its state of its neighbour
only when there is a change; contrasting DVR results in lower traffic.
a) From the received LSPs and knowledge of entire topology, a router
can then calculate the shortest path between itself and each network.
45. 45
Types of links
When the link between two routers is broken, the administrator may create a virtual
link between them using longer path that probably goes through several routers
46. 46
Link State Advertisement (LSA)
5 Types of LSAs
To share information about the neighbourhood, each entity
distribute link state advertisements (LSAs).
Info. exchange within
inside an Area
Info exchange
between different
Areas inside an AS
Info exchange
outside across
different AS
Info exchange
to external
internet
47. 47
Router link
A router link advertisement defines the links of a true router.
A true router uses this advertisement to announce information about all
its links and what is at the other side of the link (neighbour).
48. 48
Network link
A network link advertisement defines the links of a network.
A designated router on behalf of the transient network distributes this
types of LSA packet. The packet announces the existence of all the
routers connected to the network.
49. 49
Summary link to network
Router and network link advertisements flood each area with info about the router
links and network links within/inside an area. But a router must also know about the
networks outside its area, and the area border routers can provide this information.
An area border router is active in more than one area. It receives router link and
network link advertisements and creates a routing table for each area.
area border
router R1
area border
router R2
Backbone network
50. 50
Summary link to AS boundary router
The previous advertisement lets every router know the cost to reach all networks
within/inside an AS. But what about the network outside the AS? If a router inside an
area wants to send a packet outside the autonomous system, it should first know the
route to an AS boundary router; the summary link to AS boundary router provides
this information. The border routers can then flood their areas with this information.
51. 51
External link
Although the previous advertisement lets each router know the route to different AS
boundary router, this information is not enough. A router inside an AS also wants to
know which networks are available outside the AS; i.e. the external internet.
The external link advertisement provide this information. The AS boundary router
floods the AS with cost of each network outside the AS, using a routing table created
by an exterior routing table protocol. Each advertisement announces one single
network. If there is more than one network. Separate announcements are made.
52. 52
ExampleExample In the figure below, which router(s) sends out
router link LSAs? and which router(s) sends out
network link LSAs?
SolutionSolution
All routers advertise router link LSAs.
R1 has two links, Net1 and Net2.
R2 has one link, Net2 in this AS.
R3 has two links, Net2 and Net3.
53. 53
Solution ContinueSolution Continue
All three network must advertise network link LSAs:
Advertisement for Net1 is done by R1 because it is the only router
and therefore the designated router.
Advertisement for Net2 can be done by either R1, R2, or R3,
depending on which one is chosen as the designated router.
Advertisement for Net3 is done by R3 because it is the only router
and therefore the designated router.
54. 54
In OSPF, all routers haveIn OSPF, all routers have
the samethe same Link State databaseLink State database..
• Every router in an area receives the router link and network link
LSAs and form a link state database.
• Every router in the same area has the same link state database.
• A link state database is a tabular representation of the topology of
the internet inside an area. It shows the relationship between each
router and its neighbors including the metrics used.
• To calculate its next-route in the routing table, each router applies
the Dijkstra algorithm to its state database, to find the shortest path
between 2 points on a network, using a graph (nodes and edges).
• The algorithm divides the nodes into two sets: tentative and
permanent. It chooses nodes, makes them tentative, examines them,
and if they pass the criteria, makes permanent.
55. 55
Graph representation of AS:
nodes and edges
(a) An autonomous system. (b) A graph representation of (a).
56. 56
1. Start with the local node (router): the root of the tree.
2. Assign a cost of 0 to this node and make it the first permanent node.
3. Examine each neighbour node of the node that was the last
permanent node.
4. Assign a cumulative cost to each node and make it tentative.
5. Among the list of tentative nodes
a. Find the node with the smallest cumulative cost and make it permanent.
b. If a node can be reached from more than one direction
i. Select the direction with the shortest cumulative cost.
6. Repeat steps 3 to 5 until every node becomes permanent.
Dijkstra’s AlgorithmDijkstra’s Algorithm
Shortest Path Search
58. 58
Shortest Path Search
The steps used in computing the shortest path from A to D.
The arrows indicate the working node – permanent label.
The cost can relates to
delay
The label on each node can be TENTATIVE or PERMANENT
Start search and
compare with
tentative label
Mark permanent
when shortest
node found
Once permanent
never changed
Tentative node
can always be
search and
relabelled
Tentative label
change
64. 64
Link state routing table for router A
Each router uses the shortest-path tree
method to construct its routing table.
Network Cost Next router Other infor
N1 5
N2 7 C
N3 10 D
N4 11 B
N5 15 D
65. 65
Link State Routing (LSR)
Idea Behind LSR: Each router must do the following:
1. Discover its neighbors, learn their network address. (Send HELLO
packet)
2. Measure the delay or cost to each of its neighbors. (Send ECHO packet)
3. Building Link State packet telling all it has just learned. (ACK flag)
4. Distribute/Send this packet to all other routers (Flooding – SEND flag).
5. Compute the shortest path to every other router. (Dijkstra’s algorithm)
In effect the complete topology and all the delays are experimentally
measured and distributed to every router, then Dijkstra’s algorithm can
be run to find the shortest path to every other router.
HELLO packet can be acknowledged by a reply to signal its present.
ECHO packet requires instant response to know the round-trip-time.
66. 66
OSPF Packets
• Based on Link State Routing
• OSPF messages are transported directly
in IP packets
• OSPF standard supports novel concepts
such as type of service routing, load
balancing and authentication
67. 67
Building Link State Packets (LSP)
(a) A subnet. (b) The link state packets for this subnet.
Building the link state packets is easy. The difficult part is to determine
when to build them.
One possibility is to build them periodically at regular intervals.
The other is to build when some significant even occurs; i.e. a line or
neighbour going down or coming back up again.
68. 68
Distributing the Link State Packets (LSP)
Above is the packet buffer at router B. Routers A, F, C are directly
connected to B. Each row corresponds to a recently-arrived, but as
yet not fully processed LSP. The table shows where the packet
originated, sequence number, age and the data.
The process of distributing the LSP is called Flooding
Arriving packets
69. 69
LSR potential problems
1. If a router ever crashes, it will lose track of its
sequence number and starts from 0 again; next
arriving good packet will be rejected as duplicate.
2. If a sequence number is ever corrupted.
**?
The solution to all above is to introduce an ‘Age’ field for each packet
after the sequence number and decrement it once per second. When the
Age hits zero, the information from that router is discarded. The Age
field is also decremented by each router during initial flooding process,
to make sure no packets can get lose and live for indefinite period of time
Solution
70. 70
Compute the shortest path
• When a router has accumulate a full set of link state packets,
it can build the entire subnet graph because every link is
represented.
• Every link is in fact, represented twice, once for each
direction. E.g AB – 4, BA – 4.
• The two values can be averaged or used separately
• Next, Dijkstra’s algorithm can be run locally to find the
shortest path to all possible destinations. The results can be
installed in the routing tables and normal operation resumed.
• For a subnet with n routers, each of which has k neighbours,
therefore memory required to store the input data is
proportional to k*n.
72. 72
BGP & Path Vector Routing (PVR)
a) Border Gateway Protocol (BGP) is an inter-domain or inter-
autonomous system routing protocol: routing between different ASs.
b) BGP uses path vector routing to update the routing table in an area.
c) DVR and LSR are not suitable candidates for inter-AS routing :
• DVR: there are occasions in which the route with the smallest hop count is not
the preferred route; non-secure path although the shortest route taken.
• LSR: internet is too big for this routing method to require each router to have a
huge link state database. Taking very long time to calculate the routing table.
a) PVR defines the exact paths as an ordered list of ASs that a packet
should travel thru to reach the destination (besides having the
destination network and next router info.) in its routing table.
b) Security and Political issues involved: more desired to avoid ‘unsaved’
paths/routes/ASs than to take a shorter route.
c) The AS boundary router that participate in PVR advertise the routes
of the networks in their own AS to neighbour AS boundary routers.
d) Solve the count-to-infinity problem
73. 73
Path vector packets
•Each AS has its ‘speaker’ router/node that acts on behalves of the AS. Only
speaker router can communicate with other speaker routers.
•R1 send a path vector message advertising its reachability of N1. R2 receives
the message, updates its routing table and after adding its AS to the path and
inserting itself as next router, send message to R3. R3 receives the message,
updates its routing table, make changes and sends the message to R4.
74. 74
BGP – the Exterior Gateway Routing Protocol
•Instead of periodically advertise to its neighbours the cost to each destination,
each BGP router tells its neighbour the exact path it is using. e.g. F receives
information from its neighbour routers to reach D.
•Can solve count-infinity problem: suppose G is down; then IFGCD and
EFGCD routes are discarded since G’s state will be know immediately render
BCD as only choice.
After all paths are in, router F
examines them to see which is
the best & quickly drop I & E
as they pass thru itself.
PVR
75. 75
Path Vector Routing Policy
a) Policy routing can be easily implemented through path vector routing.
b) When a router receives a message from its neighbour, the speaker
node or AS boundary router can check the path with its approved list
of ASs.
c) If one of the ASs listed in the path is against its policy, the router can
ignore that path entirely and that destination.
d) For any unapproved paths, the router does not update its routing table
with this path, and it does not send the PV message to its neighbours.
e) This means that the routing table in path vector routing are not based
on the smallest hop count (as in distance vector routing) or the
minimum delay metric (as in open shortest path first routing); they are
based on the policy imposed on the router by the administrator.
f) The path was presented as a list of ASs, but is in fact, a list of
attributes. Each attributes gives some information about the path. The
list of attributes helps the receiving router make a better decision
when applying its policy. (Well-known & Optional)
76. 76
Types of BGP messages
a) Open: To create a relationship, a router running BGP opens a
connection with a neighbouring AS and sends an open message. If the
neighbour accepted, it responds with a Keep-alive message to
establish relationship between the two routers.
b) Update: The heart of BGP protocol used by router to withdraw
destination that have been advertised previously, announce a route to
a new destination or do both. (Withdraw several but advertise only
one).
c) Notification: sent by a router whenever an error condition is detected
79. 79
Due to time limitation and the vast-scope of the network layer,
we will NOT go into any more detail about Multicast.
Interested students can find more detail in “Internetworking with
TCP/IP vol.1” by Douglas Comer, Section-10.22 and Forouzan’s
Chapter-21.
Too much to take in!!!
- Brain Freeze?
80. 80
Further Reading
1- “Computer Networks”, Andrew Tanenbaum, 4th
Ed. to learn more
about the generic network layer.
2- “Internetworking with TCP/IP vol.1”, Douglas Comer, 4th
Ed.,
provides a detailed and comprehensive presentation of TCP/IP.
3- “Data Communications and Networking”, Behrouz Forouzan, 4th
Ed., when you get confused and wonder if there’s a simpler
explanation of all these issues.
Copyright Information : Some figures used in this presentation have been
either directly copied or adapted from several books.
Editor's Notes
A Routing Protocol is a combination of rules and procedures that lets routers in an internet inform each other of changes. It allows routers to share whatever they know about the internet or their neighbourhood.
The routing algorithm is that part of network layer software responsible fro deciding which output line and incoming packet should be transmitted on.
Host-specific routing is inefficient, used for specific purposes such as checking the route or providing security measures.
224 – 11100000
Mask – subnet mask. Used to get subnet address.
176 – 10110000
224 – 11100000
-----------------------
10100000 – 160
Range: 101 00000 – 160
101 11111 – 191
Total 32-2=30 hosts in this subnet.
Measured from J, JA = 8 JI = 10 JH = 12 JK = 6
Compute JG, JAG = 8+18 = 26; JIG = 10+31 =41; JHG = 12+6 = 18; JKG = 6+31 =37
When a router is added to a network, it initializes a routing table for itself, using it configuration file. The table contains only the directly attached networks and the hop counts, which are initialized to 1. The next-hop field, which identifies the next router, is empty.
Updating the Routing Table
Each routing table is updated upon receipt of RIP messages using the RIP updating algorithm shown previously. Figure 21.6 shows our previous autonomous system with final routing tables.
Slow response to infinite loop problem.
OSPF uses LSR to update the routing tables in an area.
A point-to-point link connects two routers without any other host or router n between. Each router has only one neighbour at the other of the link.
Transient link is a network with several routers attached to it. Each router has many neighbours.
Stub link is a network that is connected to only one router. The data packet enter and leave the network through this same router.
R1 is an area border router. It has two routing tables, one for area 1 and one for area 0. router R1 floods area 1 with information about how to reach a network located in area 0.