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Routers- Definition and Types

Routers
Routers are physical devices that join multiple wired or wireless networks together. A Router is a Layer-3 Device. A router is similar to a switch, but it can also connect different logical networks or subnets and enable traffic that is destined for the networks on the other side of the router to pass through. Routers can connect networks that use disimilar protocols. Routers also typically provide improved security functions over a switch. Unroutable protocols can’t be fowarded. Routers Can filter out network traffic also.

However, they filter based on the protocol addresses defined in OSI layer 3(the network layer), not based on the Ethernet packet addresses. Note that protocols must be routable in order to pass through the routers. A router can determine the most efficient path for a packet to take and send packets around failed segments. Routers can regenerate signals, concentrate multiple connections, convert data transmission formats, and manage data transfers. They can also connect to a WAN, which allows them to connect LANs that are separated by great distances. More technically, a router is a networking device whose software and hardware are usually tailored to the tasks of routing and forwarding information. Routers connect two or more logical subnets, which do not necessarily map one-to-one to the physical interfaces of the router.

Internal Components of a Router

Router Memory

Basically there are 4 types of Memories in a Router, and these are:
• Boot ROM
• Flash
• RAM
• NVRAM

Boot ROM: It stores the mini IOS (Internet work Operating System) image (RX Boot) with extremely limited capabilities and POST routines and core level OS for maintenance.

FLASH: It is an EPROM chip that holds most of the IOS Image. It maintains everything when router is turned off.

RAM: RAM holds running IOS configurations and provides caching. RAM is a volatile memory and looses its information when router is turned off. The configuration present in RAM is called Running configuration.

NVRAM: It is a re-write able memory area that holds router’s configuration file. NVRAM retains the information when ever router is rebooted. Once configuration is saved, it will be saved in NVRAM and this configuration is called Startup Configuration.

Types of Routers

There are 2 types of Routers we have:

• Modular Routers
• Fixed Routers

Modular Routers:- These type of routers have up gradable slots, and the number of ports can be increased just by adding cards in the slots.

Fixed Routers:- These types of routers have fixed number of ports.

Configuration of a Router

Router for the first time is configured through the CONSOLE port.COM port of a PC is connected to the console port of router with a console cable by using a transceiver. Router is accessible by a tool. In windows, it is called HYPER TEMINAL. As soon as the router is powered on and accessed, the following things happen,

POST—>BOOT STRAP—->FLASH [ROM (mini IOS) If IOS is Corrupted]—>NVRAM—->Setup Mode

In Setup mode, there will be a message,
“Would You Like To Enter The Initial Configuration [Y/N]” :
If “Y” then, initial configuration starts.
If “N” would you like to terminate the auto installation?
Press “RETURN” to get started……You will land on the default prompt of the Router “ ROUTER >”.
Router>_

Working Modes of a Router

Three main modes of a Router are :
• User Mode (Default mode)
• Privilege or Administrative Mode
• Global Configuration Mode

USER MODE: Router> is the user mode, I,e the default prompt. It means that when ever a router boots successfully it lands into the user mode. Router cannot be configured from this mode, but it is used for just monitoring purpose.
Router> en
Router#

PREVILEGE MODE: Router# it is the administrating mode, we can check whether the settings and configurations made have been implemented or not. Eg. “Router # Sh int e0”. If it is new router all the interfaces are by default shut down, so the message will be, “ Ethernet 0 is administratively down, line protocol is down.”

Global Configuration Mode: As the name indicates, it is a global configuration mode I,e. we can configure any interface from this mode, just by entering into the interface mode.
Router# Config t
Router (Config)#

Some more modes of a Router are

• Interface Configuration Mode
• Line Configuration Mode
• Router Mode
• Sub-Interface Mode

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