A router is a network device that forwards information packets among PC networks. Routers perform traffic routing functions on the Internet. Data sent over the Internet, such as a website or email, is in the form of data packets. Packets are typically forwarded from one router to another through the networks that make up the internetwork until they reach their destination node. the router is connected to two or more data lines from different IP networks. When a packet of data arrives at either line, the router reads the network address information in the packet header to determine its final destination. It then uses information in its routing table or routing policy to forward the packet to the next network. The most common types of IP routers are home routers and small office routers, which simply forward IP packets between your home computer and the Internet. More advanced routers such as Enterprise routers connect large corporate or ISP networks to powerful core routers to transfer data at high speeds over fiber optic lines of the internet backbone.
Router Components:
The major components of the router are:
Processor or CPU:
Routers are powered by a high-performance multicore processor that supports high-speed multiple LAN and WAN connections and can run multiple concurrent services. The CPU in the router executes commands and processes the command in the operating system. The flow of data in the interface is controlled by the CPU. The CPU used in routers are generally, RISC-based CPUs.
Memory:
The router involves different types of memory that are mentioned below:
- Read Only Memory (ROM): ROM stores the bootstrap startup program of the router along with the operating system software and other test programs like POST programs (Power On Self-Test).
- Flash Memory: Flash memory mostly known as flash holds the IOS images. The flash content is used by the router at the time of reload. Flash is erasable and reprogrammable ROM.
- Random Access Memory (RAM): RAM stores information such as routing tables and running configuration files. RAM is volatile; hence, its content is lost during router power down and reload.
- Non-volatile RAM (NVRAM): NVRAM stores the startup configuration files. It is non-volatile RAM; hence contents are not lost during router power down and reload.
Ports and Interfaces:
Interfaces connect routers to other devices. Data travels through these interfaces in the network. Ports and interfaces are identified by their name and number. Different types of Ports and Interfaces are mentioned below:
- Standard Ethernet: It is the basic type of Ethernet defined in the IEEE 802.3 standard. Ethernet supports 10Mbps data speed. The transmission media supported for the Ethernet is 10Base-T.
- Fast Ethernet: Fast Ethernet port also called the Fe port, provides a higher data transmission rate of up to 100 Mbps. Fast Ethernet is defined in IEEE 802.3u standard. The transmission media supported for fast Ethernet is 100Base-T, 100Base-TX, 100Base-FX, etc.
- Gigabit Ethernet: Gigabit Ethernet is the next-level Ethernet technology that provides a ten times higher data rate than fast Ethernet. It can have a data transmission rate up to 1000 Mbps and is defined in IEEE 802.3z. The transmission media supported for the Gigabit Ethernet are 1000Base-T, 1000Base-LX, 1000Base-SX, etc.
- Serial Interface: The serial interface is used for WAN connectivity. Separate modules and cards are added to the router for serial connection. It is used for point-to-point links. Serial connection between routers has two ends DCE (Data Communication Equipment) and DTE (Data Terminating Equipment).
- ISDN (Integrated Services Digital Interface): ISDN is a circuit-switched network that provides simultaneous digital services for voice as well as data over an ordinary analog telephone line.
- Console Port: The console port is used for the management and configuration of the router. The console port of the router is connected to the COM port of the PC or laptop using a Console cable. The hyper-terminal session is established between the router and the PC to access the router.
- Auxiliary Port: Auxiliary Port (AUX) connects the router remotely in the non-network environment. The dialup modem is used for the end-to-end connectivity between the auxiliary port of the router and the remote PC. This allows a network to access the router from a remote location.
- Loopback Interface: The lookback interface is not the physically available port in the router. The loopback interface is the “Always On” port which is used as router ID when we configure OSPF protocols in the router and for diagnostics and troubleshooting purposes.
Router Boot Process:
The router goes through the following steps during the boot process:
- The router is powered on.
- POST is performed which checks the hardware components including memory and interfaces.
- The bootstrap program is loaded and executed.
- Bootstrap reads the configuration register value which defines how the router will boot up.
- Depending on the value of the configuration register, the bootstrap program finds and locates the IOS image.
- If the bootstrap fails to load the IOS it will drop the boot sequence to ROMMON (ROM Monitor) mode for troubleshooting.
- If the IOS is loaded it finds and loads the configuration.
- If the configuration is not present, the system configuration dialog would be launched.
- If the configuration is loaded, you would be presented in the CLI interface.