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Ca Ex S2 M01 Introduction To Routing And Packet Forwarding
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Ca Ex S2 M01 Introduction To Routing And Packet Forwarding



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  • 1. CCNA – Semester 2 Chapter 1 - Introduction to Routing and Packet Forwarding CCNA Exploration 4.0
  • 2. Objectives • Identify a router as a computer with an OS and hardware designed for the routing process. • Demonstrate the ability to configure devices and apply addresses. • Describe the structure of a routing table. • Describe how a router determines a path and switches packets 2
  • 3. Inside the Router 3
  • 4. Routers are Computers • Routers have many of the same hardware and software components that are found in other computers including: – CPU – RAM – ROM – Operating System 4
  • 5. Routers are Computers Routers are at the network center • A router connects multiple networks. This means that it has multiple interfaces that each belong to a different IP network. • Each network that a router connects to typically requires a separate interface. These interfaces are used to connect a combination of both Local Area Networks (LANs) and Wide Area Networks (WANs). 5
  • 6. Routers are Computers Routers determine the best path • The primary responsibility of a router is to direct packets destined for local and remote networks by: – Determining the best path to send packets – Forwarding packets toward their destination 6
  • 7. Routers are Computers Routers determine the best path 7
  • 8. Routers are Computers Routers determine the best path 8
  • 9. Routers are Computers Routers determine the best path 9
  • 10. Routers are Computers Routers determine the best path 10
  • 11. Router as a Computer • Describe the basic purpose of a router – Computers that specialize in sending packets over the data network. They are responsible for interconnecting networks by selecting the best path for a packet to travel and forwarding packets to their destination • Routers are the network center – Routers generally have 2 connections: • WAN connection (Connection to ISP) • LAN connection Not common: • PSTN connection •… 11
  • 12. Evolution of Routers • Multiprotocol devices providing pure data delivery with minimal access control and QoS. • Intelligent Network Services, this allowed us to provide security capabilities like integrated firewall and encryption. • Integrated voice and data capabilities, allowing routers to provide voice gateway features for IP telephony. • Today the router is an integrated platform for providing advanced services in security, content delivery, and voice. 12
  • 13. Cisco Router Series 13
  • 14. Router Components • Router components and their functions”  CPU - Executes operating system instructions  Random access memory (RAM) - Contains the running copy of configuration file. Stores routing table. RAM contents lost when power is off  Read-only memory (ROM) - Holds diagnostic software used when router is powered up. Stores the router’s bootstrap program.  Non-volatile RAM (NVRAM) - Stores startup configuration. This may include IP addresses (Routing protocol, Hostname of router)  Flash memory - Contains the operating system (Cisco IOS)  Interfaces - There exist multiple physical interfaces that are used to connect network. Examples of interface types: • Ethernet / FastEthernet interfaces • Serial interfaces • Management interfaces 14
  • 15. Router Components 15
  • 16. Router Components 16
  • 17. Cisco router 1841’s Architecture - Front Panel LED Color Status SYS PWR Green Router has successfully booted up and the software is functional. Slow, steady blinking when system is booting or in the ROM monitor. SYS ACT Green Blinking when packets are transmitted or received on any WAN or LAN interface, or when monitoring system activity. CF Blinking Flash memory is busy. Do not remove the CompactFlash memory card green when this light is on. 17
  • 18. Router Components • Router components 18
  • 19. Internetwork Operating System • Cisco IOS manages the hardware and software resources of the router, including memory allocation, processes, security, and file systems. Cisco IOS is a multitasking operating system that is integrated with routing, switching, internetworking, and telecommunications functions. • Cisco creates many different types of IOS images, depending upon the model of the router and the features within the IOS. • The command line interface (CLI) is a much more common method of configuring Cisco routers. 19
  • 20. Router Boot-up Process Bootup Process • There are four major phases to the bootup process: 1. Performing the POST 2. Loading the bootstrap program 3. Locating and loading the Cisco IOS software 4. Locating and loading the startup configuration file or entering setup mode 20
  • 21. Router Boot-up Process 21
  • 22. Router Boot-up Process 22
  • 23. Router Boot-up Process • Verify the router boot-up process: – The show version command is used to view information about the router during the bootup process. Information includes:  Platform model number  Image name & IOS version  Bootstrap version stored in ROM  Image file name & where it was loaded from  Number & type of interfaces  Amount of NVRAM  Amount of flash  Configuration register 23
  • 24. Router Boot-up Process Verifying Router Bootup Process • The show version command can be used to help verify and troubleshoot some of the basic hardware and software components of the router. 24
  • 25. Router Interfaces • Router Interface is a physical connector that enables a router to send or receive packets • Each interface connects to a separate network • Consist of socket or jack found on the outside of a router • Types of router interfaces: – Fixed – Modular 25
  • 26. Router Interfaces • Two major groups of Router Interfaces – LAN Interfaces:  Are used to connect router to LAN network  Has a layer 2 MAC address  Can be assigned a Layer 3 IP address  Usually consist of an RJ-45 jack – WAN Interfaces  Are used to connect routers to external networks that interconnect LANs.  Depending on the WAN technology, a layer 2 address may be used.  Uses a layer 3 IP address 26
  • 27. Router Interfaces 27
  • 28. Routers and the Network Layer • The main purpose of a router is to connect multiple networks and forward packets destined either for its own networks or other networks. • A router is considered a Layer 3 device because its primary forwarding decision is based on the information in the Layer 3 IP packet, specifically the destination IP address. This process is known as routing. 28
  • 29. Routers and the Network Layer • Routers Operate at Layers 1, 2, and 3 29
  • 30. CLI Configuration and Addressing 30
  • 31. Implementing Basic Addressing Schemes • When designing a new network or mapping an existing network, document the network. At a minimum, the documentation should include a topology diagram that indicates the physical connectivity and an addressing table that lists all of the following information: – Device names – Interfaces used in the design – IP addresses and subnet masks – Default gateway addresses for end devices, such as PCs 31
  • 32. Implementing Basic Addressing Schemes 32
  • 33. Implementing Basic Addressing Schemes 33
  • 34. Basic Router Configuration Basic Router Configuration • Router name • Passwords • Banner 34
  • 35. Basic Router Configuration • Router Interface Configuration 35
  • 36. Basic Router Configuration • Verifying Basic Router Configuration – Issue the show running-config command – Save the basic router configuration by Issuing the copy running-config startup-config command • Additional commands that will enable you to further verify router configuration are:  show running-config - Displays configuration currently in RAM  show startup-config - Displays configuration file NVRAM  show ip route - Displays routing table  show interfaces - Displays all interface configurations  show ip interface brief - Displays abbreviated interface configuration information 36
  • 37. Building the Routing Table 37
  • 38. Introducing the Routing Table • The primary function of a router is to forward a packet toward its destination network, which is the destination IP address of the packet. • Routing Table is stored in RAM and contains information about:  Directly connected networks - this occurs when a device is connected to another router interface  Remotely connected networks - this is a network that is not directly connected to a particular router  Detailed information about the networks include source of routing information, Network address & subnet mask, and ip address of next-hop router, exit interface • show ip route command is used to view a routing table 38
  • 39. Introducing the Routing Table • Directly Connected Routes • Static Routes • Dynamic Routes 39
  • 40. Directly-Connected Networks • Once the interface is "up," the network of that interface is added to the routing table as a directly connected network. 40
  • 41. Static Routing • Static routes in the routing table – Includes: network address and subnet mask and IP address of next hop router or exit interface – Denoted with the code S in the routing table – Routing tables must contain directly connected networks used to connect remote networks before static or dynamic routing can be used • When to use static routes – When network only consists of a few routers – Network is connected to internet only through one ISP – Hub-and-spoke topology is used on a large network 41
  • 42. Static Routing 42
  • 43. Dynamic Routing • Dynamic routing protocols are used by routers to share information about the reachability and status of remote networks. Dynamic routing protocols perform several activities, including: – Network discovery – Updating and maintaining routing tables 43
  • 44. Dynamic Routing • Dynamic routing features: – Automatic Network Discovery: allows the routers to automatically learn about these networks from other routers. – Maintaining Routing Tables: automatically share routing information with other routers and compensate for any topology changes without involving the network administrator. • IP Routing Protocols: – RIP (Routing Information Protocol) – IGRP (Interior Gateway Routing Protocol) – EIGRP (Enhanced Interior Gateway Routing Protocol) – OSPF (Open Shortest Path First) – IS-IS (Intermediate System-to-Intermediate System) – BGP (Border Gateway Protocol) 44
  • 45. Routing Table Principles • 3 principles regarding routing tables:  Every router makes its decisions alone, based on the information it has in its routing table.  One router’s information in the routing table may not be the same as another router’s routing table.  Routing information about a path to a network does not provide information on how to return to the original network. 45
  • 46. Routing Table Principles 46
  • 47. Routing Table Principles 47
  • 48. Routing Table Principles 48
  • 49. Routing Table Principles 49
  • 50. Path Determination and Switching Functions 50
  • 51. Packet Fields and Frame Fields • Internet Protocol (IP) packet format contains fields that provide information about the packet and the sending and receiving hosts • Fields that are importance for CCNA students: – Destination IP address – Source IP address – Version & TTL – IP header length – Precedence & type of service – Packet length 51
  • 52. Packet Fields and Frame Fields • MAC Layer Frame Format • MAC Frames are also divided into fields. They include: – Preamble – Start of frame delimiter – Destination MAC address – Source MAC address – Type/length – Data and pad – Frame check sequence 52
  • 53. Best Path and Metric • A Metric is a numerical value used by routing protocols to assess a given route • Metrics may be based on a single path variable or multiple variables of a path • 2 types of metrics used by routing protocols are: – Hop count - this is the number of routers a packet must travel through to get to its destination – Bandwidth - this is the “speed” of a link also known as the data capacity of a link 53
  • 54. Router Paths and Packet Switching • Equal cost metric is a condition where a router has multiple paths to the same destination that all have the same metric • To solve this dilemma, a router will use Equal Cost Load Balancing. This means the router sends packets over the multiple exit interfaces listed in the routing table. • Equal Cost Paths and Unequal Cost Paths: a router can send packets over multiple networks even when the metric is not the same if it is using a routing protocol that has this capability. 54
  • 55. Path Determination • The path determination function is the process of how the router determines which path to use when forwarding a packet by searching its routing table. • One of three path determinations results from this search: – Directly connected network – Remote network – No route determined 55
  • 56. Switching Function • Switching Function of Router is the process used by a router to switch a packet from an incoming interface to an outgoing interface on the same router. • A packet received by a router will do the following:  Strips off layer 2 headers.  Examines destination IP address located in Layer 3 header to find best route to destination.  Re-encapsulates layer 3 packet into layer 2 frame.  Forwards frame out exit interface. 56
  • 57. Switching Function • Step 1: PC1 has a packet to be sent to PC2 57
  • 58. Switching Function • Step 1: PC1 has a packet to be sent to PC2 58
  • 59. Switching Function • Step 1: PC1 has a packet to be sent to PC2 59
  • 60. Switching Function • Step 2: Router R1 receives the Ethernet frame 60
  • 61. Switching Function • Step 2: Router R1 receives the Ethernet frame 61
  • 62. Switching Function • Step 2: Router R1 receives the Ethernet frame 62
  • 63. Switching Function • Step 2: Router R1 receives the Ethernet frame 63
  • 64. Switching Function • Step 2: Router R1 receives the Ethernet frame 64
  • 65. Switching Function • Step 2: Router R1 receives the Ethernet frame 65
  • 66. Switching Function • Step 3: Packet arrives at router R2 66
  • 67. Switching Function • Step 3: Packet arrives at router R2 67
  • 68. Switching Function • Step 3: Packet arrives at router R2 68
  • 69. Switching Function • Step 3: Packet arrives at router R2 69
  • 70. Switching Function • Step 3: Packet arrives at router R2 70
  • 71. Switching Function • Step 3: Packet arrives at router R2 71
  • 72. Switching Function • Step 3: Packet arrives at router R2 72
  • 73. Switching Function • Step 4: The packet arrives at R3 73
  • 74. Switching Function • Step 4: The packet arrives at R3 74
  • 75. Switching Function • Step 4: The packet arrives at R3 75
  • 76. Switching Function • Step 4: The packet arrives at R3 76
  • 77. Switching Function • Step 4: The packet arrives at R3 77
  • 78. Switching Function • Step 4: The packet arrives at R3 • Step 5:The Ethernet Frame with encapsulated IP packet arrives at PC2 78
  • 79. Switching Function • Step 5: The Ethernet Frame with encapsulated IP packet arrives at PC2 1. PC2 examines the destination MAC address, which matches the MAC address of the receiving interface, its Ethernet NIC. PC2 will therefore copy the rest of the frame into its buffer. 2. PC2 sees that the Ethernet Type field is 0x800, which means that the Ethernet frame contains an IP packet in the data portion of the frame. 3. PC2 decapsulates the Ethernet frame and passes the IP packet to the IP process of its operating system. 79
  • 80. Summary 80
  • 81. Configuration Register Setting – 1800 Series • The order in which the router looks for system bootstrap information depends on the boot field setting in the configuration register. • The configuration register is a 16-bit register in NVRAM. • To ensure that the upper 12 bits are not changed, first retrieve the current values of the configuration register using the show version command. • Then use the config-register command, changing only the value of the last hexadecimal digit. 81
  • 82. Configuration Register 82
  • 83. Configuration Register Boot Field Configuration Register Bit Descriptions Boot Field Meaning (Bits 3, 2, 1, and 0) 0000 At the next power cycle or reload, the router boots to the ROM monitor. (0x0) 0001 Boots the first image in flash memory as a system image. (0x01) 0010 - 1111 At the next power cycle or reload, the router sequentially processes each (0x02 - 0xF) boot system command in global configuration mode that is stored in the configuration file until the system boots successfully. If no boot system commands are stored in the configuration file, or if executing those commands is unsuccessful, then the router attempts to boot the first image file in flash memory. 83
  • 84. Configuration Register 84
  • 85. 85