What is the router?


Router or an admin or router ( in English : the router ), is a device used in computer networks for routing data packets among them. Routers control the movement of data in the Internet . Packets are carried in a network from router to router, from their source until they reach their destination.

A router connects two or more networks, and communicates directly with each network through one of its ports . Each network has its own address space. The router port hosts a network address. When one of the router ports receives a data packet, it reads the information in the packet header , specifically The destination address, then searches for its equivalent in its routing table , or according to the routing policy followed, the router then decides to route the packet towards its destination, and according to its position on the packet path, it determines its path to an appropriate neighboring network or the appropriate next router, or delivers it to its final destination.

Router definition.

A router is a network device consisting of a set of hardware and software used to connect two or more different subnets by wired and wireless signals, and is used in wide area networks (WANs) such as the Internet. The router operates at the network layer, which is the third layer of the layers that the OSI (Open System Interconnection) has termed.

Hardware and software.

▪️ Routing or routing today is often associated with IPv4 , while migration to IPv6 has involved IPv6 routing.

▪️ The first routers in the 1960’s were simply ordinary miniature computers. Although standard computers can be used for routing, modern routers generally include additional hardware to speed up critical tasks such as packet transmission. These specialized routers are not always compatible with (IPv6), a small size memory Non-volatile able to save the main tuning in case of breach of sector moments.

▪️ Existing data transmission paths play a similar role through voice telephone exchanges.

This type of equipment does not require magnetic storage:



3. Juniper.

4. Speedtouch.

5. Chronos trendchip made in Taiwan.

6. Avaya Avaya.

There are many types for larger tasks:

Type for receiving a DSL signal or local loop ( closed circuit )

2. A type of network connection.

Router action levels.

The router works on two levels:

1.Control level: It finds the best route (or interface) to send data to the receiver.

2.Passing and Transfer Level: It performs the actual transfer of the received data from the receiving interface to the sending interface chosen in the previous stage.

The router relies on the routing table to find the shortest path for data.

Router types.

Routers have several types in terms of size and service offered:

1.Small Office Home Office (SOHO) Routers.

2.Routers to service providers and large organizations.

The most popular types of routers are those produced by CISCO. But they are relatively expensive. Below are the Cisco routers sections.

Sections of routers.

We will study as an example the CISCO routers sections.The router consists of a mother board on which the CPU, memory and other internal parts are located:


A read-only memory contains the source code for the basic functions. It contains four basic components:

▪️ (power on self test) Post:The first thing that is loaded upon boot is to check the hardware.

▪️ Bootstrap: Every operating system has two types of files: boot files and system files.

Bootstrap files to load system files.Bootstrap is the cisco bootloader, and it owns the path to the boot files.

▪️ Mini IOS: It is automatically downloaded from the ROM. It represents a small group of CISCO IOS .

▪️ ROM Monitor: You can use it to boot manually using commands.

2.Memory Flash.

It is a type of memory used to store a compressed copy of the files of the CISCO IOS system , usually in which a single file is located. The size of this memory varies by chain and router type and ranges from 8-64 KB. BootStrap loads the iOS system from Flash in the normal boot process. The show flash command is used to display information about this memory and its contents.


It is a random access memory, but it is ephemeral. It does not permanently save data. It includes the current settings of the router. It also provides us with an interface to deal with the user. This interface directly affects the performance of the router, and the system files in it are uncompressed and are known as the settings launcher.

The show running configuration command is used to detect the state of this memory.

4.Sustainable NVRAM.

This memory is used to store configuration (start-up) files and this type of random access memory (RAM) does not lose its color when the router is restarted or powered off.


A router is a connection point with multiple interfaces, each interface connects to a different network, and the router transmits data passing between these networks through the interfaces.

Each interface has its own address.

There are many interfaces available on the router such as the Ethernet cable interface for LAN and a series of synchronous and asynchronous interfaces for WAN, the number and type of these interfaces varies according to the router series and type. A router has at least one Ethernet port and one WAN port (usually ISDN BRI). Some routers display commands related to interfaces such as:

▪️ The show interface command that displays the complete status of all interfaces in the router.

▪️ Show interface serial 0 command that displays the full status of a particular interface.

▪️ Show ip interface brief command that displays short, concise but sufficient information such as IPaddresses, and the status of each interface on the router.

Boot sequence in cisco routers.

1.Run a POST self-check.

2.Download and run the bootstrap code.

3.Search for system software.

4.System software download.

5.Find settings.

6.Load settings.


Finding the system cisco IOS.

After loading the bootstrap, the system CISCO IOS is initially searched , in the case of normal booting, it searches for the copy of the system files in Flash memory, and if it is not there, it tries to boot from the network. If there is any problem with the boot network, then RXBOOT mode works, and if we do not succeed, we have the last option to put ROMMON. Sort searches:

1.Check the registry settings.

2.Check the NVRAM settings.

3.Flash searches in memory.

4.Attempts to boot from the network.

5.Resort to RXBOOT mode.

6.Resort to ROMMON mode.

Note: To try to boot from the network we must know the IPs of the nearby routers and this is possible through the help of CDP (CISCO.Discovery Protocol) CISCO Discovery Protocol

Reference :

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