A router is basically a computer like PC. We we see now all about router hardware components and what are they doing inside router
Routers have many of the same hardware and software components that are found in computers:
- Operating System
CPU – The CPU executes operating system instructions like booting up, routing functions, and switching functions.
RAM – RAM is volatile memory that needs power to keep its content. When the router reboots RAM is deleted entirely. The RAM stores data that needs to be executed. RAM is used to store Operating System, Running Configuration File, IP Routing Table, ARP Cache and Packet Buffer.
- Operating System – In the case of Cisco devices that is “Cisco IOS” – Internetwork Operating System. IOS is copied into RAM during bootup.
- Running Configuration File – Is the configuration file that stores the configuration commands that the router IOS is currently using. Almost all the configuration commands on the router are stored in the running configuration file, called running-config.
- IP Routing Table – File that stores information about directly connected and remote networks. It is used to determine the best path to forward the packet.
- ARP Cache – Cache that contains the IPv4 address to MAC address mappings. It’s like ARP cache on a PC. The ARP cache is used on routers that have LAN interfaces such as Ethernet interfaces.
- Packet Buffer – Temporarily stored packets are atored in a buffer when received on an interface or before they exit an interface.
This is only RAM, volatile memory. However, the router also contains permanent storage areas, such as ROM, flash and NVRAM.
ROM – ROM is a form of permanent storage. If we are looking at Cisco devices, they store bootstrap instructions, Basic diagnostic software and Scaled-down version of IOS in this kind of memory. In the ROM we can find firmware that is made of the software that does not normally need to be modified or upgraded, such as the bootup instructions.
Flash Memory – Flash memory is nonvolatile computer memory that can be stored and erased electrically. Flash is used to permanently store the operating system. Flash memory does not lose its contents when the router loses power or is restarted.
NVRAM – Nonvolatile RAM also does not lose its information when power is turned off. NVRAM is used by the Cisco IOS as permanent storage for the startup configuration file (startup-config).