Cisco router hardware structure

A Cisco router is a network device that connects multiple networks or CIDR blocks. It can translate data from different networks or CIDR blocks ", so that they can "read" each other's data to form a larger network. A vro consists of hardware and software. The hardware is mainly composed of physical hardware and circuits such as the central processor, memory, interface, and control port. The software is mainly composed of the IOS operating system of the router. At www.2cto.com, we will take the Cisco router that is currently widely used as an example to introduce the hardware composition and working conditions of the router. Let everyone know about their composition while using them. Like a computer, a router also contains a central processor (CPU ). Vrouters of different generations and models have different CPUs. Cisco routers generally use two processors: Motorola 68030 and Orion/R4600. The CPU of the router is responsible for configuration management of the router and data packet forwarding, such as maintaining various tables and routing operations required by the router. The data packet processing speed of the router depends largely on the type and performance of the CPU. The memory router uses the following memory types, each of which assists the router in different ways. 1. read-only memory (ROM) Read-only memory (ROM, Read. ly Memory) features in Cisco routers are similar to ROM in computers. It can only be read but cannot be written. It is usually used to store the program data written by the manufacturer, write can be performed only under specific professional conditions. If you want to upgrade, replace the ROM chip. ROM mainly includes: 1) system power-on self-check code (POST), used to check whether each hardware part of the router is in good condition; 2) System Boot Code (BootStrap ), it is used to start the router and load it to the IOS operating system. 3) the backed up IOS operating system is used when the original IOS operating system is deleted or damaged. Generally, this IOS version is lower than the current version running IOS, but it is enough to enable the router to start and work. 2. Flash Memory (Flash) is a readable and writable memory that can still store data after the system is restarted or shut down. Flash stores IOS in use. In fact, if the Flash capacity is large enough, you can even store multiple operation systems, which is very useful for IOS upgrades. If you do not know whether the new version of IOS is stable, you can retain the old version of IOS after the upgrade. When a problem occurs, you can quickly return it to the old version of the operating system to avoid long-term network faults. 3. non-volatile RAM (NVRAM) non-volatile RAM is a readable and writable memory that can still store data after the system is restarted or shut down. NVRAM is only used to save the Startup configuration file (Startup-Config), so its capacity is small. Generally, only 32 KB ~ is configured on the vro ~ NVRAM of kb. At the same time, NVRAM is fast and costly. 4. random memory (RAM) www.2cto.com RAM is also a readable and writable memory, but its contents will be cleared after the system is restarted or shut down. Like RAM in a computer, RAM in a Cisco router is also a storage for temporarily storing operating systems and data during operation, allowing the router to quickly access this information. RAM has a higher access speed than the preceding three types of memory. During running, RAM contains route table items, ARP buffer items, log items, and groups waiting for sending in queue. In addition, it also includes Running configuration files (Running-config), Code being executed, IOS operating system programs, and some temporary data information. The reading method of IOS code varies depending on the vro type. For example, Cisco 2500 series routers only read part of IOS from Flash when needed, while Cisco 4000 Series routers must load all of IOS into RAM before running. Therefore, the former is called the Flash running device (Run from Flash), and the latter is called the RAM running device (Run from RAM ). PS: RAM has two categories: Static RAM and Static RAM/SRAM. The speed of SRAM is very fast. It is currently the fastest reading and writing storage device, but it is also very expensive. So it is only used in demanding places, such as the first-level buffer of the CPU and second-level slow flushing. The other is Dynamic RAM, Dynamic RAM/DRAM. Dynamic RAM is slower than SRAM, but faster than any ROM. The computer memory is DRAM. DRAM can only keep data for a short time. To keep data, DRAM must be refreshed every other time. If the storage unit is not refreshed, data will be lost. Router power-on START process: 1) system hardware power-on self-check. Run the hardware detection program in the ROM to check whether each component works normally. After completing the hardware check, start software initialization. 2) software initialization process. Run the BootStrap program in ROM for initial boot. 3) search for and load IOS system files. IOS system files can be stored in multiple places. As to which IOS is used, you can specify them by using commands. 4) after IOS is loaded, the system searches for the saved Startup-Config file in NVRAM for system configuration. If the Startup-Config file exists in NVRAM, the file is transferred to RAM and executed one by one. Otherwise, the system enters the Setup mode and performs initial router configuration. Www.2cto.com all vro interfaces have interfaces. Each Interface has its own name and number. The full name of an interface consists of its type mark and number, which starts from 0. For routers with fixed interfaces (such as Cisco 2500 series) or routers with modular interfaces (such as Cisco 4700 series), only one number is used in the full name of the interface, serial numbers are carried out based on the physical order of the routers. For example, Ethernet0 indicates 1st Ethernet interfaces and Serial1 indicates 2nd serial ports. For vrouters that support "online plugging and deletion" or that have dynamic physical interface configuration changes, the full name of the interface must contain at least two numbers separated by a slash. 1st digits represent the slot number, and 2nd digits represent the port number in the interface card. For example, in a Cisco 3600 router, seri_3/0 represents the 1st serial ports located on slot 3. For vrouters that support "universal interface processor (VIP)", the interface number is in the form of "slot, port adapter, and port number", for example, in a Cisco 7500 series router, ethernet4/0/1 refers to the 1st Ethernet interfaces of the 2nd port adapters on slot 4. The Console port is installed on all routers of the Console port so that users or administrators can use the terminal to communicate with the router to complete router configuration. The port provides an EIA/TIA-232 asynchronous serial interface to configure the router locally (the first configuration must be done through the Console port ). The vro has different models and different interface methods for connecting to the console. Some use the DB25 connector.