Computers can also route the difference between a router and a computer

Now let's take a look at the similarities and differences between Cisco routers and other computers on the Interconnect network. Routers are similar to other computers in that they also have memory, operating system, configuration, and user interface (operating systems in Cisco routers, known as the Interconnection network operating system Internetworkoperatingsystem or iOS, all of which are owned by Cisco). Like other computers, routers have a boot process that loads the bootstrapper from ROM and enables the computer to load its operating system and configuration into memory.

Routers differ from other computers in the configuration of the user interface and memory.

1. Type of memory for routers

In a typical DOS and UNIX system, storage is physically divided into multiple storage bodies, each of which is assigned different functions by the software. Routers also have multiple storage bodies, each of which is used for different functions. The functionality of these storage bodies varies with the router.

Table 1-1 shows the use of various types of storage in routers.

(1) Rom

Read-only memory (ROM) contains a copy of the iOS used by the router. The ROM chip of the 7000 series router is located on the Router processor board and 4000 of the ROM chip is on the motherboard. In 7000 and 4000, the ROM chip can be upgraded to a newer version of iOS. In the 2500 router and 1000 series LAN Extender, the ROM chip cannot be upgraded and contains only a very limited operating system, with only routing features. In the 2500-series router, iOS is located in Flash memory.

When running a ciscoios below version 11, if you connect a terminal to the console port during boot time, you will see a 2500 series flaw. Romios The configuration file is checked, most commands will not be recognized. This causes many error messages to appear on the screen, which is normal. When iOS in flash memory is mounted, there is usually no more error messages to display.

(2) Ram

Random access memory (RAM) is divided into shared memory and main memory by iOS. Main memory is used to store the router configuration and the iOS data structure associated with the routing protocol. For IP, main memory is used to maintain the road by tables and ARP tables, and for IPX, main memory is used to maintain SAP and other tables. Shared memory is used to cache packet packets that are waiting to be processed. This type of memory is used only by the 4000 and 2500 series routers. In the 7000 router, there is an Exchange processor that controls the packet flow through the router.

(3) Flash (flash memory)

The flash memory keeps the current version of iOS running on the router. ROM content cannot be rewritten, and flash memory is erasable and can be written to flash memory for a new version of iOS.

(4) NVRAM

Non-volatile RAM (Nonvolatileram,nvram) is not lost when the power is off. The router configuration information is stored in the NVRAM.

2. Boot router

The router's boot process is similar to that of a PC, and the process is as follows:

1 loader boot from ROM.

2 from flash loading into the operating system (IOS, interconnection network operating system).

3 Locate and load the configuration file in the NVRAM, or in the preconfigured network server. If the configuration file does not exist, the router enters setup mode.