Routing

Topics: Routing, IP address, Computer network Pages: 16 (1948 words) Published: July 13, 2013




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Identify a router as a computer with specialised hardware and operating system designed for routing Give a router a basic configuration including IP addresses Routing tables Router activities – finding the best paths and switching packets

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Connect networks together Find best routes Switch packets from one network to another Do this efficiently 24/7 Provide security by permitting or denying specified types of packet Provide quality of service by prioritising packets



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CPU: control unit handles instructions, ALU for calculations RAM: volatile working storage ROM: permanent storage for POST and startup instructions Operating System: software that runs the computer System bus, Power supply







Long term storage is Flash and NVRAM, not hard disk Range of different interfaces all on different networks No input/output peripherals. Connect via a console PC and use PC’s keyboard and screen


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Dynamic random access memory: as in a PC Temporary memory while the router is on Loses content when the router loses power or is restarted Holds running configuration Holds routing tables Holds ARP cache Holds fast-switching cache etc.



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Non-volatile RAM: keeps its contents when the router is off Stores the startup configuration file When you have configured a router, you must save your configuration to NVRAM if you want to keep it



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Electronically erasable, programmable ROM (EEPROM) Keeps its contents when the router is off Holds the operating system image (IOS) Allows the IOS to be updated Can store multiple versions of IOS software if it has enough capacity Can be upgraded by adding SIMMs



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Permanent memory: cannot be upgraded without replacing the chip Holds power-on self test (POST) instructions Stores bootstrap program Stores ROM monitor software (for emergency download of IOS, for password recovery) May store basic IOS for emergency use (less common than it was)

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ROM Permanent Holds POST, boot instructions, basic IOS

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Flash Keeps contents Holds IOS image


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NVRAM Keeps contents Holds startup configuration file


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RAM Volatile Holds runnning config, tables, queues etc







Can be attached directly to the motherboard (like our Fast Ethernet interfaces) Can be on removable and interchangeable modules (like our serial interfaces) Modules for different serial connections









As specialised computers, routers and switches need operating systems. Cisco devices use the Cisco Internetwork Operating System (IOS) There are versions for different models of router and switch, and different feature sets The IOS can be upgraded periodically

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Platform-features-format-version c2600-i-mz.122-8.T5 c2600 is the platform: Cisco 2600 series router i is a code for the set of features in this IOS, another is ipbase mz is a code to say that the IOS runs in RAM and the file is zip compressed 122-8.T5 is the upgrade version









The IOS is stored in the router’s flash memory, often in compressed form Most routers copy the IOS to RAM when they start up You need enough space in flash and in RAM if you upgrade the IOS Some of our routers have more features than others – it depends on the IOS.



ROM monitor:
◦ Used to recover from system failure or loss of password ◦ Needs direct access from console port



Boot ROM (optional, may not have this):
◦ Used when upgrading IOS



Cisco IOS
◦ Normal operation, stored in Flash, runs in RAM

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Run POST and bootup instructions from ROM Load IOS file from flash Load configuration from NVRAM Fully operational


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Has 4 hex digits – that’s 16 binary digits Configuration register is saved in NVRAM show version to see its value Value of last hex digit tells how to load IOS Usual is 0x2102...
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