How to configure a Router and what is Cisco IOS?

Now a days,every company maintains standard operating systems.For example, IBM uses Citrix Net scaler OS and Cisco uses its won IOS(Internetwork Operating System).In older posts,we studied what is a router and cisco heirarchical model.Everyone goes on studying and studying.....for Cisco exams (e.g.CCNT,CCNA,CCNP and CCIE etc) but how many are confident to show router startup.???

Here I am giving the techniques of router startup and it's configuration.

Router Startup:

• Boot process steps 
• Test hardware 
• Load bootstrap program 
• Locate and load the Cisco IOS 
• Locate and load the router configuration file

Introduction to Cisco IOS?

-Almost all current Cisco routers and switches run Cisco IOS (Internetwork Operating System),

the routing and switching software in Cisco devices.

- Cisco IOS command-line interface (CLI) is the text-based user interface to a Cisco device for

configuring, administering, and managing the Cisco device.

- CLI can be accessed through:

i) Console with a rollover cable and terminal emulator application. [line console 0]

ii) AUX through a dialup device such as modem for out-of-band management. The modem

is connected with a straight-through cable to the auxiliary port. [line aux 0]

iii) In-band management through the network via Telnet or SSH. [line vty 0 4]

- Below lists the main Cisco IOS modes:

User EXEC mode: Least privileges and limited access. Only provides a set of nondestructive show commands that allow examination of configuration.

Privileged mode: More show commands, and limited configuration commands.

Configuration mode: Configuration commands are being entered in this mode. Unable to check status with the series of show commands. Sub-divided into some child modes.

eg: interface configuration mode, line configuration mode, router configuration mode, etc.
         Commands entered in this mode update the active or running configuration immediately after the Enter button is pressed.
         Configuration commands can be divided into global configuration commands and sub-commands, eg: interface sub-command,sub-interface subcommand, controller subcommand, line sub-command,router subcommand, etc.

- Below describes some basic Cisco IOS commands:

enable - Switches from EXEC mode to Privileged mode

disable - Switches from Privileged mode back to EXEC mode.

show version - Views the basic configuration of the system hardware, software version, the name and source of the system boot image, etc.

configure terminal - Switches from Privileged mode to Global Configuration mode.

hostname -Changes the hostname of a Cisco device.

^Z / end / exit -Exits from the Global Configuration mode back to Privileged mode.

exit / quit - Exits from the EXEC mode.

- Some special IOS CLI features are Context-Sensitive Help with [?] and Auto-Completion with

[TAB] can be used to display or auto-complete the available commands or parameters.

Cisco Hierarchical Model

-Defined by Cisco to simplify the design, implementation, and maintenance of responsive,

scalable, reliable, and cost-effective networks.

- The 3 layers are logical and not physical – there may be many devices in a single layer,

or a single device may perform the functions of 2 layers, eg: core and distribution.

                                               Figure : The Cisco Hierarchical Model

- Below are the 3 layers in the Cisco Hierarchical Model:

Core layer: Also referred to as the backbone layer. It is responsible for transferring large amounts of traffic reliably and quickly – switches traffic as fast as possible. Afailure in the core can affect many users; hence fault tolerance is the main concern in this layer. The core layer should be designed for high reliability,high availability, high speed, and low convergence. Do not support workgroup access, implement access lists, VLAN routing, and packet filtering which can introduce latency to this layer.

Distribution layer: Also referred to as the workgroup layer. Its primary functions are routing,Inter-VLAN routing, defining or segmenting broadcast and multicast domains,network security and filtering with firewalls and access lists, WAN access,and determining (or filtering) how packets access across the core layer.

Access layer : Also referred to as the desktop layer. Here is where end systems gain access to the network. The access layer (switches) handles traffic for local services(within a network) whereas the distribution layer (routers) handles traffic for remote services. It mainly creates separate collision domains. It also defines the access control policies for accessing the access and distribution layers.

- In a hierarchical network, traffic on a lower layer is only allowed to be forwarded to the upper

layer after it meets some clearly defined criteria. Filtering rules and operations restrict

unnecessary traffic from traversing the entire network, which results in a more responsive

 (lower network congestion), scalable (easy to grow), and reliable (higher availability) network.

- A clear understanding of the traffic flow patterns of an organization helps to ensure the

placement of network devices and end systems within the organization.

what is router and what are its components?

Router:
A router is a more sophisticated network device than either a switch or a hub. Like hubs and switches, network routers are typically small, box-like pieces of equipment that multiple computers can connect to. Each features a number of "ports" the front or back that provide the connection points for these computers, a connection for electric power, and a number of LED lights to display device status. While routers, hubs and switches all share similiar physical appearance, routers differ substantially in their inner workings.

Traditional routers are designed to join multiple area networks (LANs and WANs). On the Internet or on a large corporate network, for example, routers serve as intermediate destinations for network traffic. These routers receive TCP/IP packets, look inside each packet to identify the source and target IP addresses, then forward these packets as needed to ensure the data reaches its final destination.

Routers for home networks (often called broadband routers) also can join multiple networks. These routers are designed specifically to join the home (LAN) to the Internet (WAN) for the purpose of Internet connection sharing. In contrast, neither hubs nor switches are capable of joining multiple networks or sharing an Internet connection. A home network with only hubs and switches must designate one computer as the gateway to the Internet, and that device must possess two network adapters for sharing, one for the home LAN and one for the Internet WAN. With a router, all home computers connect to the router equally, and it performs the equivalent gateway functions.

Additionally, broadband routers contain several features beyond those of traditional routers. Broadband routers provide DHCP server and proxy support, for example. Most of these routers also offer integrated firewalls. Finally, wired Ethernet broadband routers typically incorporate a built-in Ethernet switch. These routers allow several hubs or switches to be connected to them, as a means to expand the local network to accomodate more Ethernet devices.

In home networking, hubs and switches technically exist only for wired networks. Wi-Fi wireless routers incorporate a built-in access point that is roughly equivalent to a wired switch.

Cisco 2500series Router

Router Components

• Bootstrap – stored in ROM microcode – brings router up during initialization, boots router and loads the IOS.
• POST – Power On Self Test - stored in ROM microcode – checks for basic functionality of router hardware and determines which interfaces are present 
• ROM Monitor – stored in ROM microcode – used for manufacturing, testing and troubleshooting 
• Mini-IOS – a.k.a RX-BOOT/boot loader by Cisco – small IOS ROM used to bring up an interface and load a Cisco IOS into flash memory from a TFTP server; can also perform a few other maintenance operations
• RAM – holds packet buffers, ARP cache, routing table, software and data structure that allows the router to function; running-config is stored in RAM, as well as the decompressed IOS in later router models.
• ROM – starts and maintains the router. 
• Flash memory – holds the IOS; is not erased when the router is reloaded; is an EEPROM [Electrically Erasable Programmable Read-Only Memory] created by Intel, that can be erased and reprogrammed repeatedly through an application of higher than normal electric voltage 
• NVRAM – Non-Volatile RAM - holds router configuration; is not erased when router is reloaded.
• Config-Register -  controls how router boots; -  value can be seen with “show version” command; -  is typically 0x2102, which tells the router to load the IOS from flash memory and the startup-config file from NVRAM.