Cisco Certified Network Associate (CCNA)

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Cisco Certified Network  Associate (CCNA)

The networking industry is highly competitive, and evolving technology only increases in its complexity. Cisco has stayed at the forefront of the tidal wave, maintaining a dominant wave in the industry. Cisco provided a means to meet the growing demand for experts in the field of networking and therefore introduced several intermediate certifications to achieve that purpose.

However, Cisco’s CCNA focuses on Routing and Switching and also the ability to install configure and troubleshoot local area network (LAN), using Cisco proprietary devices and also multi-vendor devices as well as a little introduction on wide area networks (WAN).

A network is basically all the components (hardware and software) involved in connecting computers and applications across small and large distances for the purpose of sharing resources.

When designing and maintaining a network, some factors must be considered;
• Cost.
• Security
• Speed
• Topology
• Scalability
• Reliability
• Availability.

Components of a network.
Some important and key components of a network include;
• Applications
• Protocols
• Pc
• File server
• Hub, bridges, routers.
• Wireless and access points. Etc

• Personal area network (PAN): – this is a network within an office, a small office home office (SOHO).
• Local area network (LAN): – this is a connection of two or more personal area networks around a particular geographical area.
• Campus area network (CAN):- a campus area network is a connection of two or more local area network.
• Metropolitan area network (MAN):- a metropolitan area network is a connection of two or more networks across a city.
• Wide area network (WAN):- this is a connection of two or more networks that runs through very long distances.

Network topology is the logical or physical arrangement of computers and network devices. There are various types of network topology;
• Bus topology:- In bus topology, all components are connected to and share a single trunk wire.
• Point-to-point topology:- A point-to-point topology has a single connection between two component, here two component can directly communicate without interference.
• Star/ extended star topology:- In a star topology, a central device has many point-to-point connections to other components. Star topologies are used in environments in which many components need to be connected. An extended star topology is basically multiple interconnected star topologies.
• Mesh topology:- Meshing generally describes how components are connected together. Two types of meshed topologies are always used, the partially meshed and the fully meshed. In a partially meshed environment, every device is not connected to every other device while in a fully meshed environment every device is connected to every other device.
• Ring/Dual ring topology:- In a ring topology, device one is connected to device two and device two to three and so on to the last device, which connects back to the first device. Ring topology can be implemented with a single ring or dual ring. Dual rings are typically used when you need redundancy.

In 1984, the international organization for standardization (ISO) developed the OSI reference model to describe how information is transferred from one networking component to another. ISO developed the seven-layer model to help vendors and network administrators inter-operate and gain better understanding on how data is handled and transported between layers, as well as to provide guidelines for the implementation of new networking standards and technologies. To assist in this process, the OSI Reference Model separates the network communication process into seven layers.

The OSI Reference Model comprises of seven layers, the application layer, presentation layer, session layer, transport layer, network layer, data-link layer and physical layer.

Ethernet is a LAN technology that functions at the data-link layer. Ethernet uses the carrier sense multiple access/ collision detection (CSMA/CD) mechanism to send information in a shared network. Ethernet was initially developed with the idea that many devices would be connected to the same piece of wiring. The acronym CSMD/CD describes the process on how Ethernet operates in a shared network.

In a traditional, or hub based Ethernet environment, only one NIC can successfully send a frame at a time. Before an Ethernet NIC puts a frame on the wire, it will first sense the wire to ensure no other frame is on the wire. If it a copper wire for example, it uses the voltage level to sense and if fiber, it uses it frequencies. If there is already a frame on the wire, it waits until it delivered before sending it own. However, since the Ethernet support multiple accesses, when two or more devices simultaneously send a frame, a collision occurs, in this situation, the voltage level of the copper and light frequency of the fiber get messed up. If the NIC sees a collision for their transmitted frames, there have to resend the frames, with each creating a signal known as “jam signals” which help to notify each point the period of time to wait, and when this is done, it then listens again and retransmit her original frame. This delay is always in microseconds and therefore impossible for humans to detect.

Collision domain/ broadcast domain.
Collision domain is experienced when you have your LAN and so every device in a LAN creates a collision domain. Broadcast domain describes a boundary to which a particular traffic can be limited to. Every interface in a switch has its own collision domain but belong to a single broadcast domain. Every interface in a hub has a single collision domain and a single broadcast domain. Every interface in a router has its own collision domain and its own separate broadcast domain

Encapsulation and De-encapsulation.
Message Encapsulation is the process of adding control information (frames) to a data as it moves from one layer to the other. De-encapsulation is the reverse of encapsulation; it’s the process of removing the control information for the user to access.

Source Mac-address. Source I.P address. 25 Data. 110 Destination IP-address. Destination Mac- address.

An encapsulated frame.

Mac addressing.

A MAC address is 48 bit long is a represented as a hexadecimal. It is 12 character in length, where each character is 4 bits. The Mac address is represented in a dotted decimal format like FFFF.FFFF.FFFF. The first 6 digits are associated with the vendor or maker of the NIC, and it called the organizationally unique identifier (OUI) and the last 6 is used to represent the NIC card. Each NIC has a unique Mac address within the same physical or logical segment. a logical segment is a VLAN and it referred to as a broadcast domain. However, some devices allow you to change the hardware address while some don’t.

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Bit values.

Computer and networking components process everything in binary. In one byte (octet), there are 8 bits. Each bit in a byte when enabled (turned on) represent a specific decimal value. To convert the binary byte value to a decimal value, you look at all the bits that are turned on, and add up the equivalent decimal value.

Bit position 8 7 6 5 4 3 2 1
Decimal value 128 64 32 16 8 4 2 1

For example, assume we had a byte with a value of 11000001, bits 8, 7 and 1 are turned on, so when we add up their corresponding decimal value, 128 + 64 + 1 = 193. If all the bits where 0, then their decimal value will be 0, but if there were 1, then their decimal values will be 1.

Hexadecimal conversion.

Decimal binary Hexadecimal
1 0001 1
2 0010 2
3 0011 3
4 0100 4
5 0101 5
6 0110 6
7 0111 7
8 1000 8
9 1001 9
10 1010 A
11 1011 B
12 1100 C
13 1101 D
14 1110 E
15 1111 F

Ethernet cabling.

LANs typically uses either copper or fiber optics. Copper cabling can include one strand of copper through which electric voltage is transmitted and fiber optics uses light emitting diodes (LEDs) and lasers to transmit data. With this, light is used to represent a 1 or 0. When light is on the wire, then it represents a 1, but if it not, then 0.

Unshielded twisted pair.

Between copper and fiber, implementing copper is less expensive. The Ethernet standard defined three types of copper cabling;

a. Thick net : uses thick coaxial cable (out-dated)

b. Thin net: uses a thin copper cable (out-dated).

c. Unshielded twisted pair: uses a four-pair wire, where each pair is periodically twisted. This cable is uses today because it cheaper to install, configure and troubleshoot and it also has the ability to transmit up to 150-500m before ATENUATION. Some of the cables in this category include;

·               Cat 1:- used for telephone connections. (Unsuitable for data).

·               Cat 2 :- used for data connection up to 4Mbps. (token ring)

·               Cat 3:- used for data connection up to 10Mbps. (Ethernet).

·               Cat 4:- used for data connection up to 16Mbps.

·               Cat 5:- used for data connection up to 100Mbps.

·               Cat 5e:- used for data connection up to 1Gbps.

·               Cat 6:- used for connections up to 1Gbps (24- gauge).

Data Connection Equipments (DCE)

This is equipments that neither generate signals nor modify them, their major function is to receive signals and communicate them immediately to other devices. Example hubs, switches and bridges.

Data Termination Equipments (DTE).

These are equipments that generate, modify or terminate signals. Example of such include routers, pc and file server.

During cable construction, some important component must first be present, RJ45 crimper, RJ45 cables (cat5, cat5e or cat6), RJ45 connectors and probable a LAN tester. Three types of cables are always required;

·      Cross over cable: used during connections among a particular category, like when connecting DTE – DTE or DCE – DCE connections.

·      Straight through cable: used during connections of different categories. Like connecting a DTE – DCE or DCE – DTE.

·      Roll over cable: a roll over cable is used during console connection. It’s used for an out-of-bound management for configuring devices through the console port.


Switches and bridges are layer 2 networking devices, used for interconnecting two or more networks and network components. Though our focus will be on the switch because it a more intelligent device than the hub. Switches are more recent technology, and the accepted way of building today’s networks. With switching, each connection gets a “dedicated bandwidth” and can operate at full speed. Bridges and switches have three major functions;

Listening function: switches and bridges go through a listening function by paying attention to the directly connected device to learn their Mac address.

Learning Mac address: the switch then learns the Mac address of it neighboring switch and save it port number and Mac address on her content addressable memory (CAM) table, as a frame comes into the port of a switch, it checks it source address and then go back to her CAM table to verify if it has the address in it, if it doesn’t, it includes it immediately in it CAM table and forwards the frame.

Forwarding frames: whenever a frame comes into a port, it don’t just check it source address but also the destination address and then examines it to know if it associated with the same port as the source of the frame, if it not, it drops the packet but if it is, then the frame is forwarded. Some examples if network frames include;

·      Unicast frames: this frame is sent from one person to just one person in the network.

·      Multicast frames: this frame is sent from one person to some persons in the network.

·      Broadcast frames: broadcast frames are frames that are sent to everybody in a particular network. This is possible with a directed broadcast address of FFFF.FFFF.FFFF.

Ø  Layer 2 loop removal: looping is the continuous repetition of bandwidth or signal within a particular network or broadcast domain. This is possible through a protocol known as spanning tree protocol (STP).


Duplexing affects how a device can send and receive frames in Ethernet. Two modes are used in duplexing, half and full. With half duplex, the device can either send or receive, it cannot do both simultaneously. Full duplex on like the half duplex, send and receive at the same time.

TCP/IP version 4.

The transmission control protocol/ internet protocol (TCP/IP) is a standard that includes many protocols, it defines how machines on an internetwork can communicate to each other and therefore has become the de facto standard for networking protocols. To help clarify how data moves between devices running TCP/IP, a model that looks like an OSI reference model was created.

Introduction to IPV4 addressing,.
Probably, one of the most confusing parts of the TCP/IP stack is the addresses used at the internet layer, referred to as IP addresses. This chapter introduces you to layer 3 addressing or IP addresses. IPv4 addresses are 32 bits in length, there are broken down into 4 bits (octets) separated with periods btw them. Like 11111111111111111111111111111111, these are broken into 4 octets like 11111111.11111111.11111111.11111111, and when converted to decimal, we have

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•    Types of addresses.
There are actually two types of addresses;
a.    Private IP addresses: private addresses are addresses that are use within an organization in a local area network.
b.    Public IP address: public addresses are addresses which are routable over the public network. Example is the internet, there are used to connect one network to another

Classes of IP address.
Basically, layer 3 addresses are made up of two components;
a.    The network component: the network component is used to uniquely identify every network or subnet in a given address or to which an address belongs to.
b.    Host component: the host component is used to uniquely identify every device in a particular segment or subnet.
The combination of these two components must be unique throughout the entire network. TCP/IP uses the same components for addressing, but it adds a twist to it by breaking up network numbers into five classes.

•    Class A          1st byte =network address= 8 bits
Last 3bytes = host component = 24 bits
Class A address ranges from 0 – 127 and has a default subnet mask of
Class A private address ranges from –

•    Class B       1ST 2byte = network component = 16 bits
Last 2byte = host potion = 16 bits
Class B address ranges from 128 – 191 and has a default subnet mask of
Class B private address ranges from –

•    Class C       1ST 3byte = network component = 24 bits
Last 1 byte = host component = 8 bits
Class C address ranges from 192 – 223 and has a default subnet mask of
Class C private address ranges from –

•    Class D       used for scientific purposes.

•    Class E      used for multicasting.

One of the processes associated with using IP address is that as a person, it can be difficult to remember dozens of addresses; people tend to remember names more, Domain Name Service (DNS) is used to resolve names to their corresponding IP address. To use DNS, a network component needs to define a DNS server that will handle the resolution process. You can manually define the DNS server to use or acquire them dynamically via DHCP.
3.5    Wireless LAN
This chapter provides an introduction to wireless technology. Wireless transmission has been used for a long time to transmit data by using infrared, microwave or radio wave. It is cheaper to install and implement because it doesn’t require cabling. Wireless communication can be grouped into three technologies;

•    Narrowband: when choosing a wireless solution for your LAN, speed, distance and the number of devices to connect must be taken into cognizance. Narrowband typically require a license and operate at a low data rate. Only one frequency is used for transmission, 900MHz, 2.4GHz or 5GHz
•    Broadband: broadband falls under a personal communication service (PCS). They provide lower rates than the narrowband solutions and cost the same, but provide a wider coverage.
•    Circuit and packet switch solutions: these are based on cellular technologies. They provide lower rates than the others and typically have higher fees for every megabit transmitted. However, you can easily obtain nationwide coverage from almost every cellular company. 3G is one of more cellular implementations by cellular phone companies.

Wireless standards.
The main standard bodies responsible for WLANs are IEEE and WI-FI alliance. Popular WLAN standard include 802.11a, 802.11b, and 802.11g. 802.11a uses OFDM as a transmission method, uses a 5GHz frequency and a throughput of 54Mbps. 802.11b uses a DSSS as a transmission method, uses a 2.4GHz frequency and a throughput of 11Mbps. 802.11g uses DSSS/OFDM as a transmission method, uses 2.4GHz frequency and a throughput of 54Mbps, it backward compatible with 802.11b.

WLAN implementation.
The two basic types of wireless implementation include the ad hoc mode, which allows clients to setup connections directly without an AP. And infrastructure mode which deals with security and scalability issues and clients can communicate with each other via an AP. Two components must always b necessary when connecting WLANs, Access points and Clients.

However, CCNA only focuses on familiarizing with WLAN technology as well as objects that can distort signals. Knowing about WLANs technology might not be very important as it has been removed from the CCNA objective. Nevertheless, it necessary you understand it for future use.

Subnetting is the breaking or splitting of a large network into smaller networks called subnets. Subnet mask is always used to show the difference between a network address and a host address, or to show the starting point of a network address and host address. Subnetting was actually introduced to solve the problem of insufficiency of host addresses to devices, both physical and logical. For example, a class C address has 8 bits in it host portion, meaning when you buy an IP address from your ISP, say, this is a class C address and remember, the first three portions are used to represent the network portion, your just left with the last portion which starts from 0 – 255, and which gives us 256 addresses all together, and probably your network has different departments, so u can actually subnet this one address to gives u more addresses.

However, in the 265 addresses, only 254 are assignable because the first address is always used to represent that default gateway, and the last address is known as a broadcast address, it the address that is used to forward frames and packet in that network. Let take an example of a class C address and subnet it., When converted to binary that the computer understands, we have 11111111.11111111.11111111.00000000. The contiguous ones represent the network portion and the contiguous zero represents the host portion. This address has a default subnet mask of During subnetting, one bit is borrowed from the host portion and turned on, ie 1, and so the contiguous ones becomes 25bit instead of 24 for a class A and then used for subnetting. = 11111111.11111111.11111111.1 0000000   networking bits
Network portion         host portion
Networking bits are in powers of 2.
21=2  22=4  23=8  24=16  25=32  26=64  27=128  28=256 ………..and so on, and this powers represent block sizes during subnetting.

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