Router
It’s a layer 3 device that connects 2 different networks and routes packets of data from one network to another. It breaks up Broadcast domain as well as Collision Domain.
Advantages of Router
1.Router don’t forward Broadcasts by default.
2.Perform access control on the traffic that flows through the router i.e. Packet Filtering.
3.Network Address Translation.
4.Quality of Service for particular network traffic.
5.Can be used as a DHCP relay agent.
7.Connects different VLAN’s.
Different Modes for configuring a router
1.User Mode- some basic commands like ping, telnet can be done. Prompt will be Router >
2.Execution or Privilege or Enable Mode- can view all configuration details, minimal commands like ping, telnet, and clock setting. Prompt will be Router #
3.Global Configuration Mode- where all configurations are done. Prompt will be Router(config)#
Sub Configuration Modes
1.Interface configuration mode, prompt will be Router(config-if)#
2.Router configuration mode, prompt will be Router(config-router)#
3.Line configuration mode, prompt will be Router(config-line)#
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When you configure the router using console port then you have to be physically close to the router. But you can configure a router by auxiliary port from any part of the world. You don’t need to be physically close to router. You can do this by simply connect the auxiliary port with modem instead of computer and then connect a modem with a telephone line. Then you can remotely access your router by dialing the telephone number to which the router auxiliary port is connected. Console port does not need any modem. It is used for local access and auxiliary port is for local as well as remote access. These are called hardware methods of accessing a router.
Now we will discuss software methods of accessing a router. First one is telnet. In this method you can access a router by using the telnet software. But using telnet you need a hardware port to enter in a router like serial ports or Ethernet ports. Telnet software is built in available in operating system and for telnet five telnet lines are used in a router which are called telnet line or Vty (Virtual Terminal Access). They are Vty0, Vty1, Vty2, Vty3 and Vty4. It means that five persons can telnet a router at one time.
Another method is TFTP (Trivial File Transfer Protocol) to access a router. It’s also a software method. Another is SNMP (Simple Network Management Protocol) for configuring the router. These are the software methods it can use any physical path i.e. console or aux. since we learned that every protocol needs software for implementation that is why these methods are called software methods of configuring router.
Mostly commonly two access methods are use to configure router that is console and telnet.
There are different things in router. There are serial interfaces in router for WAN connectivity and Ethernet interfaces for LAN connectivity. There are two ports con and aux con means console and aux means auxiliary. In old routers another port is AUI (Attachment Unit Interface) which is used for LAN connectivity because there are two possible topology of LAN one is Bus and the other is Star. In Bus topology the connectors are BNC and in Star topology RJ 45 connector is used. Therefore Cisco developed a generic interface AUI which can be used with Bus as well as with Star connectors. A converter or transceiver was used with AUI which provide either RJ-45 connector or BNC connector on the other side. You will only change the transceiver by changing the topology. But now a day only star topology is used in the world. So you can only see RJ-45 connector port in the router for LAN connectivity.
Router being an intelligence device has processor and memory. Processors of Cisco routers only perform network related activities it does not perform general activities like computer processors. CISCO charge half price for hardware and half price for software in routers.
There are different types of memory in router. RAM is one type of memory in router that is used for general purpose work but its nature is volatile. There is no hard disk in routers. Router operating system is called IOS (Internetwork Operating System). IOS is stored in a memory called Flash Memory which is non volatile in nature. Configuration file or config file or setting file of router is stored in NVRAM (Non Volatile RAM). All hardware related information is stored in ROM. When router boots so it perform POST (Power On Self Test) means it check all its hardware attach to it.
The startup sequence of router starts when first of all it reads its hardware information from ROM the he loads operating system from flash memory then he loads configuration file from NVRAM into RAM.
Lets configure time setting on router
# clock (it will show incomplete command means there are other things also with this command)
A# clock set (again incomplete command will be displayed. Now how I will know what portion remains next so I will use ? after set)
A# clock set ? (it will show hh:mm:ss means give time in this format)
A# clock set 13:18:33 (enter but again incomplete command take a help by placing ?)
A# clock set 13:18:35 ? (it will show dd:mm:yy means give date)
A# clock set 13:18:40 25:09:2010 (press enter)
If you want to display this time then type
A# show clock (press enter)
IOS Shortcuts Keys
Ctrl +A will take you to the start of the line
Ctrl + E will take cursor to the end of line
Ctrl + B will take cursor back one character
Ctrl + F will take cursor one character forward
Ctrl + P will show previous commands
Ctrl + N will show next commands
Ctrl + H will do the work of backspace
Ctrl + W will delete the whole word
Ctrl + U will delete complete line
