Giao thức định tuyến - Chapter 1
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Identify a router as a co pu e with a OS a d de y ou e computer an and hardware designed for the routing process. Demonstrate the ability to configure devices and apply addresses. Describe the structure of a routing table table. Describe how a router determines a path and switches packets.
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Nội dung Text: Giao thức định tuyến - Chapter 1
- Introduction to Routing and Packet Forwarding Routing Protocols and Concepts – Chapter 1 ITE PC v4.0 1 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Objectives Identify a router as a computer with an OS and de as co OS 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 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 2 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Router as a Computer Describe the basic purpose of a route bas pu er -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 components that are found in other computers including: –CPU –RAM –ROM –Operating System ITE PC v4.0 3 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Router as a Computer Router components and their functions” 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 access memory (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 during bootup. –Running Configuration File: This is the configuration file that stores the configuration commands that the router IOS is currently using. –IP Routing Table: This file stores information about directly connected and 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 routers that have LAN interfaces such as Ethernet interfaces. LAN –Packet Buffer: Packets are temporarily stored in a buffer when received on an interface or before they exit an interface. RAM is volatile memory and loses its content when the router is powered down or restarted. ITE PC v4.0 4 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Router as a Computer Router components and their functions” co Read-only memory (ROM) - Holds diagnostic software used when router is powered up. Stores the router’s bootstrap program. –ROM is a form of permanent storage. Cisco devices use ROM to store: –The bootstrap instructions –Basic diagnostic software –Scaled-down version of IOS 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 or is restarted. ITE PC v4.0 5 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Router as a Computer 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. 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 must be copied to NVRAM, where it is stored as the startup-config file. NVRAM retains its 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 -Serial interfaces -Management interfaces ITE PC v4.0 6 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Router as a Computer Router components co ITE PC v4.0 7 Chapter 1 © 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 command line interface (CLI) is a much more common method of li (CLI) configuring Cisco routers. – The CLI is used throughout this curriculum. Upon bootup, the startup-config file in NVRAM is copied into RAM and bootup the startup 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. and are immediately implemented by the IOS ITE PC v4.0 8 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Overview - Managing Cisco IOS Software (cont) Overview Managing Cisco IOS Software ITE PC v4.0 9 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Router as a Computer Major phases to the ajo router boot-up process Test router hardware Power-On Self Test (POST) Execute bootstrap loader Locate & load Cisco IOS software -Locate IOS IOS -Load IOS Locate & load startup configuration file or enter setup mode -Bootstrap program looks for configuration file ITE PC v4.0 10 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Stages of the router power-on boot sequence ITE PC v4.0 11 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Router as a Computer Major phases to the router boot-up process Step 1 and 2: Test router hardware •Power-On Self Test (POST) (POST) –During this self-test, the router executes diagnostics from ROM on several hardware components including the CPU, RAM, and NVRAM •Execute bootstrap loader –The main task of the bootstrap program is to locate the Cisco IOS and load it into RAM. –Note: At this point, if you have a console 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 IOS and Load IOS –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 scaled-down version of the IOS is copied from ROM into RAM. This version of IOS is used to help diagnose any problems and can be used to load a complete version of the IOS into RAM. –Note: A TFTP server is usually used as a backup server for IOS but it can also be used as a central point for storing and loading the IOS. ITE PC v4.0 12 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Router as a Computer Step 5 and 6: Locate & load startup configuration file or enter setup mode -After the IOS is loaded, the bootstrap program searches for the startup configuration file, known as startup-config, in NVRAM. This parameters including: •interface addresses addresses •routing information •passwords •any other configurations –If the startup-config, is located in NVRAM, it is copied into RAM as the running-config. •The IOS loads the commands in the file, one line at a time time. –If the startup configuration file does not exist in NVRAM, the router may search for a TFTP server. • If the router detects that it has an active link to another configured router, it sends a broadcast searching for a configuration file across the active link. You will eventually see message like the following one: •%Error opening tftp://255.255.255.255/network-confg opening tftp://255.255.255.255/network (Timed out) •%Error opening tftp://255.255.255.255/cisconet.cfg (Timed out) ITE PC v4.0 13 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Router as Computer Router as a Computer Locate & load startup configuration file or enter setup mode –Enter Setup Mode (Optional). If the startup configuration file can not be located the router configuration file can not be located, the router prompts the user to enter setup mode. •Setup mode is a series of questions prompting the user for basic configuration information. Setup mode is not intended to be used to enter complex router configurations and it is not complex router configurations, and it is not commonly used by network administrators. –When booting a router that does not contain a startup configuration file, you will see the following question after the IOS has been loaded: •Would you like to enter the initial configuration dialog? [yes/no]: no –Setup mode will not be used in this course to configure the router. When prompted to enter setup mode, always answer no. If you setup you answer yes and enter setup mode, you can press Ctrl-C at any time to terminate the setup process. –When setup mode is not used, the IOS creates a default running default running-config. •The default running-config is a basic configuration file that includes the router interfaces, management interfaces, and certain default information. •The default running-config does not contain any Th interface addresses, routing information, passwords, or other specific configuration information. ITE PC v4.0 14 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- show version Router as a Computer Verify the router boot-up process: -The show version command is used to view information about the router during the bootup process. Information includes: Information includes: Image name & IOS version IOS (tm) C2600 Software (C2600 (C2600-I-M), Version 12.2(28), 12 RELEASE SOFTWARE (fc5). Bootstrap version stored in ROM ROM: System Bootstrap, Version 12.1(3r)T2, RELEASE SOFTWARE (fc1) Image file name & where it was file name where it was loaded from System image file is "flash:c2600-i-mz.122-28.bin" ITE PC v4.0 15 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- show version Router as a Computer Verify the router boot-up process: Platform model number CPU Amount of RAM of RAM Some series of routers, like the 2600, use a fraction of DRAM as packet memory. Packet memory is used for buffering packets. To determine the total amount of DRAM on the router, add both numbers. In this example, the Cisco numbers. In this example, the Cisco 2621 router has 60,416 KB (kilobytes) of free DRAM used for temporarily storing the Cisco IOS and other system processes. The other 5,120 KB is dedicated for packet memory. The sum of these numbers is 65,536K, or 64 megabytes (MB) of total DRAM. ITE PC v4.0 16 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- show version Router as a Computer Verify the router boot-up process: Number & type of interfaces 2 FastEthernet/IEEE 802.3 interface(s) 2 Low-speed serial(sync/async) network interface(s) Amount of NVRAM 32K bytes of non-volatile configuration memory. NVRAM is used to store the startup startup-config file. file Amount of flash 16384K bytes of processor board System flash (Read/Write) System flash (Read/Write) This is the amount of flash memory on the router. Flash is used to permanently store the Cisco IOS. ITE PC v4.0 17 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- show version Router as a Computer Configuration register Configuration register is 0x2102 –The last line of the show version command displays the current configured value of the software fi th configuration register in hexadecimal. If there is a second value displayed in parentheses, it denotes the configuration register denotes the configuration register value that will be used during the next reload. –The configuration register has several uses, including password recovery. The factory default setting for the configuration register is 0x2102. This value indicates that th the router will attempt to load a Cisco IOS software image from flash memory and load the startup configuration file from NVRAM. –Note: The configuration register is discussed in more detail in a later course. ITE PC v4.0 18 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Configuration register The order in which the router looks for system bootstrap depends on the boot field setting in the configuration register. The default configuration register setting can be changed with the global configuration mode command config-register. Use a hexadecimal number as the argument for this command. command. The configuration register is a 16-bit register in NVRAM. The lowest four bits of the configuration register form the boot field. 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. ITE PC v4.0 19 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
- Configuration register (cont Configuration register (cont.) To enter the ROM monitor mode, set the configuration register value to 0xnnn0, where nnn represents the previous value of the non-boot field di digits. 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, configure the system to boot automatically from ROM set the configuration register to 0xnnn1, 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 commands in NVRAM, set the configuration register to 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 ROM IOS 2 - 15 = Boot system from Flash ITE PC v4.0 20 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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