introduction to routing and packet forwarding

Introduction to Routing and Packet Forwarding Introduction to Routing and Packet Forwardin g g Routing Protocols and Concepts – Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public ITE PC v4.0 Chapter 1 1 Objectives  I de ntif y a r ou t e r as a co m pu t e r with a n OS a n d de y a ou e as a co pu e a OS a d hardware designed for the routing process.  Demonstrate the ability to configure devices and Demonstrate the ability to configure devices and apply addresses.  Describe the structure of a routing table Describe the structure of a routing table .  Describe how a router determines a path and switches packets switches packets ITE PC v4.0 Chapter 1 2 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Router as a Computer  D esc ri be th e bas i c pu r pose o f a r ou t er esc be e bas c pu pose o a ou e -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 have many of the same hardware and software com p onents that are found in other com p uters pp including: –CPU –RAM –ROM ITE PC v4.0 Chapter 1 3 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public – Operating System Router as a Computer  Router com p onents and their functions” p CPU - Executes operating system instructions  such as system initialization, routing functions, and switching functions.  Random access memory (RAM) RAM stores the instructions and data needed  Random access memory (RAM) - RAM stores the instructions and data needed to be executed by the CPU. RAM is used to store these components: –Operating System: The Cisco IOS (Internetwork Operating System) is copied into RAM durin g bootu p . gp –Running Configuration File: This is the configuration file that stores the configuration commands that the router IOS is currently using. – IP Routin g Table: This file stores information about directl y connected and g y remote networks. It is used to determine the best path to forward the packet. –ARP Cache: This cache contains the IPv4 address to MAC address mappings, similar to the ARP cache on a PC. The ARP cache is used on hh LANi f h Eh i f routers t h at h ave LAN i nter f aces suc h as E t h ernet i nter f aces. –Packet Buffer: Packets are temporarily stored in a buffer when received on an interface or before they exit an interface. ITE PC v4.0 Chapter 1 4 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public RAM is volatile memory and loses its content when the router is powered down or restarted. Router as a Computer  R ou t e r co m po n e nt s a n d th e ir f u n c ti o n s ” ouecopoesadeucos Read-only memory (ROM) - Holds diagnostic software used when router is powered up. Stores the router’s bootstrap p ro g ram. pg –ROM is a form of permanent storage. Cisco devices use ROM to store: –The bootstrap instructions –Basic diagnostic software – Scaled - down version of IOS – Scaled - down version of IOS ROM uses firmware, which is software that is embedded inside the integrated circuit. – Firmware includes the software that does not normally need to be modified or upgraded, such as the bootup instructions. – ROM does not lose its contents when the router loses power ITE PC v4.0 Chapter 1 5 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public or is restarted. Rt C t R ou t er as a C ompu t e r  Router components and their functions” Non-volatile RAM (NVRAM) - Stores startup configuration. This may include IP addresses (Routing protocol Hostname of router) addresses (Routing protocol , Hostname of router) NVRAM (Nonvolatile RAM) does not lose its information when power is turned off. This is in contrast to the most common forms of RAM, such as DRAM, that requires continual power to maintain its information.  NVRAM is used by the Cisco IOS as permanent storage for the startup configuration file  NVRAM is used by the Cisco IOS as permanent storage for the startup configuration file . All configuration changes are stored in the running-config file in RAM, and with few exceptions, are implemented immediately by the IOS. To save those changes in case the router is restarted or loses power, the running-config must be copied to NVRAM where it is stored as the startup - config file NVRAM retains its must be copied to NVRAM , where it is stored as the startup - config file . NVRAM retains its contents even when the router reloads or is powered off. Flash memory - Contains the operating system (Cisco IOS) In most models of Cisco routers, the IOS is permanently stored in flash memory and copied into RAM during the bootup process, where it is then executed by the CPU. Flash consists of SIMMs or PCMCIA cards, which can be upgraded to increase the amount of flash memory increase the amount of flash memory . Interfaces - There exist multiple physical interfaces that are used to connect network. Examples of interface types: -Ethernet / fast Ethernet interfaces ITE PC v4.0 Chapter 1 6 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public -Serial interfaces -Management interfaces Router as a Computer  R ou t e r co m po n e nt s ou e co po e s ITE PC v4.0 Chapter 1 7 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Internetwork Operating System  The operating system software used in Cisco routers is known as Cisco Internetwork Operating System (IOS) Internetwork Operating System (IOS) . – Cisco IOS is a multitasking operating system that is integrated with routing, switching, internetworking, and telecommunications functions.  Although the Cisco IOS may appear to be the same on many routers, Although the Cisco IOS may appear to be the same on many routers, there are many different IOS images. – An IOS image is a file that contains the entire IOS for that router. Cisco creates many different types of IOS images, depending upon the model of the router and the features within the IOS. the router and the features within the IOS. – Typically the more features in the IOS, the larger the IOS image, and therefore, the more flash and RAM that is required to store and load the IOS.  Although some routers provide a graphical user interface (GUI), the dli i t f (CLI)i h th d f comman d li ne i n t er f ace (CLI) i s a muc h more common me th o d o f configuring Cisco routers. – The CLI is used throughout this curriculum.  Upon bootup the startup config file in NVRAM is copied into RAM and  Upon bootup , the startup - config file in NVRAM is copied into RAM and stored as the running-config file. – IOS executes the configuration commands in the running-config. Any changes entered by the network administrator are stored in the running- config and are immediately implemented by the IOS ITE PC v4.0 Chapter 1 8 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public config and are immediately implemented by the IOS . Overview - Managing Cisco IOS Software (cont) Overview Managing Cisco IOS Software (cont) ITE PC v4.0 Chapter 1 9 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public [...]... ) To enter the ROM monitor mode, set the configuration register value to 0xnnn0, where nnn represents the previous value of the non-boot field digits di it This value sets the boot field bits to 0000 binary From ROM monitor, boot the operating system manually by using the b command at the ROM monitor prompt To configure the system to boot automatically from ROM ROM, set the configuration register to. .. This value sets the boot field bits to 0001 binary To configure the system to use the boot system commands in NVRAM set the configuration register to NVRAM, any value from 0xnnn2 to 0xnnnF, These values set the boot field bits to a value between 0010 and 1111 binary Using boot system commands in NVRAM is the default Check Configuration Register value (NVRAM) 0 = ROM Monitor mode 1 = ROM IOS 2 - 15 = Boot... have physical connectors that are used t manage the router These connectors d to th t Th t are known as management ports –Unlike Ethernet and serial interfaces, management ports are not used for packet forwarding f di The most common management port is the console port –The console port is used to connect a terminal The terminal, or most often a PC running terminal emulator software, to configure the... the 2600, use a fraction of DRAM as packet memory Packet memory is used f b ff i packets d for buffering k t To determine the total amount of DRAM on the router, add both numbers In this example, the Cisco 2621 router has 60,416 KB (kilobytes) of free DRAM used for temporarily storing the Cisco IOS y processes The and other system p other 5,120 KB is dedicated for packet memory The sum of these numbers... 4 2 Check for IOS boot system commands in startup-config file (NVRAM) If boot system commands in startup-config a Run boot system commands in order they appear in startup-config to locate the IOS b If boot system commands fail, use default fallback sequence to locate the IOS (Flash, TFTP, ROM) 3 Locate and load IOS, Default fallback sequence: No IOS boot system commands in startup-config a Flash (sequential)... using the boot system command and/ or config register The settings in the configuration register g g g enable the following alternatives: Global configuration mode boot system commands can be specified to enter fallback sources If NVRAM lacks boot system commands the system by default uses the Cisco IOS software in flash memory (Tony) No b t system commands (T ) N boot t d (Tony) IOS specified in the... connection to the router, you will begin to see output on the screen Step 3 and 4: Locate & load Cisco IOS software -Locate IOS and Load IOS Locate –The IOS is typically stored in flash memory, but can also be stored in other places such as a TFTP server –If a full IOS image can not be located, a g , scaled-down version of the IOS is copied from ROM into RAM This version of IOS is used to help diagnose... setup-mode bypassed create a “skeleton” default running-config (no startup config) skeleton running config startup-config) ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 25 How a Cisco device locates and loads IOS The router can use its own fallback sequence to load the software q The router looks to the boot system commands saved in NVRAM (Tony) The router has its own default... Cisco Public 30 Routers determine the best path Router Interface is a physical connector that enables a router to send or receive packets –Each interface connects to a separate network •different IP network Typically, the interfaces connect to various types of networks, which means that different yp types of media and connectors are required Types of router interfaces: -Ethernet Ethernet -Fastethernet -Serial... packet into a data link frame ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 34 Routers determine the best path A router connects multiple networks p This means that it has multiple interfaces that each belong to a different IP network When a router receives an IP packet on one interface it interface, determines which interface to use to forward the packet onto its destination . Introduction to Routing and Packet Forwarding Introduction to Routing and Packet Forwardin g g Routing Protocols and Concepts – Chapter 1 © 2007. 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 . stores the instructions and data needed  Random access memory (RAM) - RAM stores the instructions and data needed to be executed by the CPU. RAM is used to store these components: –Operating