Jan 15, 2019



An IP address is divided into two parts: network and host parts. For example, an IP class A address consists of 8 bits identifying the network and 24 bits identifying the host. This is because the default subnet mask for a class A IP address is 8 bits long. (or, written in dotted decimal notation, What does it mean? Well, like an IP address, a subnet mask also consists of 32 bits. Computers use it to determine the network part and the host part of an address. The 1s in the subnet mask represent a network part, the 0s a host part.

Computers works only with bits. The math used to determine a network range is binary AND.

Let’s say that we have the IP address of with the default subnet mask of 8 bits (
First, we need to convert the IP address to binary:

IP address: = 00001010.00000000.00000000.00000001
Subnet mask = 11111111.00000000.00000000.0000000

Computers then use the AND operation to determine the network number:

The computer can then determine the size of the network. Only IP addresses that begins with 10 will be in the same network. So, in this case, the range of addresses in this network is –

A subnet mask must always be a series of 1s followed by a series of 0s.


Jan 9, 2019



Subnetting is the practice of dividing a network into two or more smaller networks. It increases routing efficiency, enhances the security of the network and reduces the size of the broadcast domain.

Consider the following example:

In the picture above we have one huge network: All hosts on the network are in the same subnet, which has following disadvantages:

a single broadcast domain – all hosts are in the same broadcast domain. A broadcast sent by any device on the network will be processed by all hosts.

network security – each device can reach any other device on the subnet, which can present security problems. For example, a server containing sensitive information would be in the same network as an ordinary end user workstation.

organizational problems – in a large networks, different departments are usually grouped into different subnets. For example, you can group all devices from the Accounting department in the same subnet and then give access to sensitive financial data only to hosts from that subnet.

The network above could be subnetted like this:

Now, two subnets were created for different departments: for Accounting and for Marketing. Devices in each subnet are now in a different broadcast domain.


Jan 6, 2019



TCP/IP defines five classes of IP addresses: class A, B, C, D, and E. Each class has a range of valid IP addresses. The value of the first octet determines the class. IP addresses from the first three classes (A, B and C) can be used for host addresses. The other two classes are used for other purposes (class D for multicast and class E for experimental purposes).

The system of IP address classes was developed for the purpose of Internet IP addresses assignment. The classes created were based on the network size. For example, for the small number of networks with a very large number of hosts, the Class A was created. The Class C was created for the numerous networks with the small number of hosts.

                                             Classes of IP addresses are:

For the IP addresses from Class A, the first 8 bits (the first decimal number) represent the network part, while the remaining 24 bits represent the host part. For Class B, the first 16 bits (the first two numbers) represent the network part, while the remaining 16 bits represent the host part. For Class C, the first 24 bits represent the network part, while the remaining 8 bits represent the host part.

Consider the following IP addresses: – because this is a Class A address, the first number (10) represents the network part, while the remainder of the address represents the host part (50.120.7). This means that, in order for devices to be on the same network, the first number of their IP addresses has to be the same for both devices. In this case, a device with the IP address of is on the same network as the device with the IP address listed above. The device with the IP address is not on the same network, because the first number of its IP address is different. – because this is a Class B address, the first two numbers (172.16) represents the network part, while the remainder of the address represents the host part (55.13). The device with the IP address of is on the same network, while a device with the IP address of isn’t.


The system of network address ranges described here is generally bypassed today by use of the Classless Inter-Domain Routing (CIDR) addressing.

Special IP address ranges that are used for special purposes are: – addresses used to communicate with the current network – loopback addresses – link-local addresses (APIPA)


Dec 30, 2018



The IP addresses are divided into three different types, based on their operational characteristics:

1. unicast IP addresses – an address of a single interface. The IP addresses of this type are used for one-to-one communication. Unicast IP addresses are used to direct packets to a specific host. Here is an example:

In the picture above you can see that the host wants to communicate with the server. It uses the (unicast) IP address of the server ( to do so.

2. multicast IP addresses – used for one-to-many communication. Multicast messages are sent to IP multicast group addresses. Routers forward copies of the packet out to every interface that has hosts subscribed to that group address. Only the hosts that need to receive the message will process the packets. All other hosts on the LAN will disard them. Here is an example:

R1 has sent a multicast packet destined for This is an RIPv2 packet, and only routers on the network should read it. R2 will receive the packet and read it. All other hosts on the LAN will discard the packet.

3. broadcast IP addresses – used to send data to all possible destinations in the broadcast domain (the one-to-everybody communication). The broadcast address for a network has all host bits on. For example, for the network the broadcast address would be Also, the IP address of all 1’s ( can be used for local broadcast. Here’s an example:

R1 wants to communicate with all hosts on the network and has sent a broadcast packet to the broadcast IP address of All hosts in the same broadcast domain will receive and process the packet.


Dec 26, 2018



Ethernet cables can come in two forms when it comes to wiring:
Straight-through cable

This cable type has identical wiring on both ends (pin 1 on one end of the cable is connected to pin 1 at the other end of the cable, pin 2 is connected to pin 2 etc.):

This type of cable is used to connect the following devices:

  • computer to hub
  • computer to switch
  • router to hub
  • router to switch

Computers and routers use wires 1 and 2 to transmit data and wires 3 and 6 to receive data. Hubs and switches use wires 1 and 2 to receive data and wires 3 and 6 to send data. That is why, if you want to connect two computers together, you will need a crossover cable.

This type of cable is used when you need to connect two devices that use the same wires to send and  the same wires to receive data. For example, consider connecting two computers together. If you use straight-through cable, with identical wiring in both ends, both computers will use wires 1 and 2 to send data. If computer A sends some packets to computer B, computer A will send that data using wires 1 and 2. That will cause a problem because computers expect packets to be received on wires 3 and 6, and your network will not work properly. This is why you need to use a crossover cable for such connections.


Newer devices support the Auto MDI-X capability to automatically detect and configure the required cable connection type. This removes the need for a specific cable type between certain devices. Also, note that the Gigabit Ethernet and faster standards use all four wire pairs to transfer data in both direction simultaneously.


Dec 13, 2018


                                                   TYPES OF ETHERNET CABLING

There are three cable types commonly used for Ethernet cabling: coaxial, twisted pair, and fiber-optic cabling. In today’s LANs, the twisted pair cabling is the most popular type of cabling, but the fiber-optic cabling usage is increasing, especially in high performance networks. Coaxial cabling is generally used for cable Internet access. Let’s expain all three cable types in more detail.

Coaxial cabling

A coaxial cable has an inner conductor that runs down the middle of the cable. The conductor is surrounded by a layer of insulation which is then surrounded by another conducting shield, which makes this type of cabling resistant to the outside interference. This type of cabling comes in two types, thinnet and thicknet. Both types have a maximum transmission speed of 10 Mbps. Coaxial cabling was used for computer networks, but today are largely replaced by twisted-pair cabling (Photo credit: Wikipedia)

Twisted-pair cabling

A twisted-pair cable has four pair of wires. These wires are twisted around each other to reduce crosstalk and outside interference. This type of cabling is common in most current LANs.

Twisted-pair cabling can be used for telephone and network cabling. It comes in two versions, UTP (Unshielded Twisted-Pair) and STP (Shielded Twisted-Pair). The difference between these two is that an STP cable has an additional layer of insulation that protects data from outside interferences.

Here you can see how a twisted pair cable looks like (Photo credit: Wikipedia):

A twisted-pair cable uses 8P8C connector, sometimes wrongly referred to as RJ45 connector (Photo credit: Wikipedia).

Fiber-optic cabling

This type of cabling uses optical fibers to transmit data in the form of light signals. The cables have strands of glass surrounded by a cladding material (Photo credit: Wikipedia).

This type of cabling can support greater cable lengths than any other cabling type (up to a couple of miles). The cables are also immune to electromagnetic interference. As you can see, this cabling method has many advantages over other methods but it’s drawback is that it is the most expensive type of cabling.

There are two types of fiber-optic cables:

Single-mode fiber (SMF) – uses only a single ray of light to carry data.
Multi-mode fiber (MMF) – uses multiple rays of light to carry data.

Two types of connectors are commonly used:

ST (Straight-tip connector)
SC (Subscriber connector)

Nov 25, 2018


                                   CISCO THREE-LAYER HIERACHICAL MODEL

Because networks can be extremely complicated, with multiple protocols and diverse technologies, Cisco has developed a layered hierarchical model for designing a reliable network infrastructure. This three-layer model helps you design, implement, and maintain a scalable, reliable, and cost-effective network. Each of layers has its own features and functionality, which reduces network complexity.

Here is an example of the Cisco hierarchical model:

Here is a description of each layer:

Access – controls user and workgroup access to the resources on the network. This layer usually incorporates Layer 2 switches and access points that provide connectivity between workstations and servers. You can manage access control and policy, create separate collision domains, and implement port security at this layer.

Distribution – serves as the communication point between the access layer and the core. Its primary functions is to provide routing, filtering, and WAN access and to determine how packets can access the core. This layer determines the fastest way that network service requests are accessed – for example, how a file request is forwarded to a server – and, if necessary, forwards the request to the core layer. This layer usually consists of routers and multilayer switches.

Core – also referred to as the network backbone, this layer is responsible for transporting large amounts of traffic quickly. The core layer provides interconnectivity between distribution layer devices it usually consists of high speed devices, like high end routers and switches with redundant links.