CCNA Study Guide

This tutorial explains internetworking in computer network with examples including networking devices and basic networking concepts such as CSMA/CD, collision domain and broad cast domain.


End Devices: - End devices are used to access or transmit the data. Computer, laptop, data server and tablet are the example of end devices.

Networking Devices: - Networking devices are used to control the data flow. Switches, Routers, HUB, Bridges, firewalls and modems are the example of networking devices.

Media: - Media is used to transmit the data. Copper cables, fiber cable and wireless signals are the example of media.

Following figure illustrate a simple computer network

computer network


Probably you will access PC3 from any network application such as Network [Available in left pane of windows explorer on any Windows OS] and drop the file in shared folder from PC3. That’s all, your job is done.

But wait…. it’s your job that is done not computer’s. Actually computer’s job is just started. Computer will start with name resolution process. In Name resolution process hostname is translated with IP address and vice versa. Its same mechanisms that mobile phone uses. When you dial someone’s number from contact what happen? Your mobile phone displays his name on screen. This feature allows us to know who is calling us or to whom we are calling.


mobile dns

Neither Bob nor SAM has to remember the each other’s mobile number. Because mobile numbers and contact names are stored in phonebook application. Phonebook is the smallest part of DNS service. DNS service is the database of contact numbers and names. Names are used for human reference while numbers are used for mobile network. Both are converted with each others in name resolution process. Same thing happens in computer network. You can replace name and number of mobile network with hostname and IP address in computer network.

In computer network:-


In our example we are sending a file from PC1 to PC3. Hostname of our destination address is PC3. It must be converted in IP address before PC1 can access it. PC1 uses DNS service to resolve the hostname with IP address.

Okay our source computer knows the IP address of destination computer. Will it send the file now? Not yet, it needs to know one more address; MAC address. MAC address is a hardware address and burned with Ethernet card from manufacturer.



Time  Source       Destination Protocol  Info
8.123  Broadcast   ARP       Who has Tell

A sample response from PC3 to PC1

Time    Source       Destination  Protocol  Info
Key Points

Every computer in network has a unique network address. This address represents its location in network. Computer address is built from two addresses IP address and MAC address.

IP Address: - IP address is a software address. We need to configure it on each PC.

MAC Address: - MAC address is a hardware address. It is assigned with Ethernet card from its manufacture company.

Computers know their own address but they don't know others. To know others address they use two types of broadcast ARP and RARP.


Broadcast domain






collision in computer network






  • This mechanism is only used in HUB or shared environment.
  • All devices have equal priority.
  • In this situation collision will occur.
  • Jam signal has a waiting time period.

Collision domain


Networking devices




networking device hub




networking device bridge


  • They cannot control broadcast.
  • Bridges have port limitation.



networking device switch


switch and collision


switch cam table

Switches can control the collision but they cannot control the broadcast.



networking device router

Routers have following drawback: -

  • They are very expensive
  • They have limited ports

Multilayer switches


multilayer swtich

Multilayer switches are usually deployed in enterprise size company environment.

Device Collision Broadcast
HUB Single collision domain Single broadcast domain
Bridge Per port collision domain Single Broadcast domain
Switch Per port collision domain Single Broadcast domain
Router Per port collision domain Per port broadcast domain
Multilayer switch Per port collision domain Per port broadcast domain

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