Router Memory Processors and Interfaces

The configuration file contains the configuration commands that you have typed, as well as some configuration commands entered by default by the router. The configuration file can be stored in a variety of places, including two inside a router. The router has a couple of other types of memory as well:

■ RAM—Sometimes called DRAM for dynamic random-access memory, RAM is used by the router just as it is used by any other computer: for working storage. The running or active configuration file is stored here.

■ ROM—This type of memory (read-only memory) stores a bootable IOS image, which typically is not used for normal operation. ROM contains the code that is used to boot the router until the router knows where to get the full IOS image or as a backup bootable image, in case there are problems.

■ Flash memory—Either an EEPROM or a PCMCIA card, Flash memory stores fully functional IOS images and is the default location where the router gets its IOS at boot time. Flash memory also can be used to store any other files, including configuration files.

■ NVRAM—Nonvolatile RAM stores the initial or startup configuration file.

All these types of memory, except RAM, are permanent memory. No hard disk or disk storage exists on Cisco routers. Figure 7-4 summarizes the use of memory in Cisco routers.

Figure 7-4 Cisco Router Memory Types

RAM

Flash

ROM

NVRAM

(Working Memory and Running Configuration)

(Cisco IOS Software)

(Basic Cisco IOS Software)

(Startup Configuration)

For the sake of consistency, Cisco IOS Software always uses the term interfaces to refer to the physical connections to a network. By being consistent, IOS commands familiar on one type of Cisco router will be familiar on another. Some nuances are involved in numbering the interfaces, however. In some smaller routers, the interface number is a single number. However, with some other families of routers, the interface is numbered first with the slot in which the card resides, followed by a slash and then the port number on that card. For example, port 3 on the card in slot 2 would be interface 2/3. Numbering starts with 0 for card slots and 0 for ports on any card. In some cases, the interface is defined by three numbers: first the card slot, then the daughter card (typically called a port adapter), and then a number for the physical interface on the port adapter.

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