Router is a layer three device i.e., network layer device. There are mainly two types of routers. They are:
1) Fixed interface &
2) Modular interface.
Fixed interface routers:
They are routers which can not add/remove interfaces/ports.
Modular interface routers:
They are routers which can add/remove interfaces/ports.
The ports in a router include serial port for WAN interface, Ethernet port for LAN interface, auxiliary port, console port to manage router and a BRI port to directly connect an ISDN connection. The BRI port is not used in new routers.
The main functions of routers are:
1) To find a routing path to destination network.
2) Route packets into corresponding interface by checking the routing table.
When a packet reaches the router it checks the destination ip address and then searches the entry in the routing table and it will place the packet to the corresponding interface.
Functioning method of router:
1) Learn the details of neighboring routers that are connected to reachable networks.
2) Find the exact location of destination networks.
3) Choose the correct path to reach that destination network.
4) Update the routing information in the routing table.
Router has mainly two types of components: software and hardware. The main hardware components used in a router are:
1) Processor – to process information.
2) Motherboard – it is the circuit interconnecting all peripherals.
3) Memory – permanent read/write memory (FLASH, NVRAM), temporary memory (DRAM), permanent read only memory (ROM).
4) Network interfaces
5) SMPS – switch mode power supply.
6) Chassis – component to protect all peripherals.
The ROM of router contains POST, bootstrap program, ROM monitor and mini-IOS. The Power-on-self-test conducts test on the router hardware. Then the bootstrap program brings the router up and loads the configuration files and IOS image. ROM monitor is a mini operating system through which user can perform low level testing and troubleshooting. The mini IOS is used when the IOS image cannot be loaded to the router. The RAM in router is having the same function as the RAM in a computer. It contains the running files like IOS image, routing table etc. Flash is a nonvolatile memory in which the IOS is stored. NVRAM is used to save the configuration files of the router.
Routers also contains interfaces through which data/packets is transferred to the destination. Ethernet, Fast Ethernet, serial are some of the interfaces available in a router.
The software part of the router is called IOS i.e. Internetwork Operating System.
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