How many hosts per subnet 


This will show you how to work out how many hosts per subnet on a class C network

Let's say you have been given the subnet mask of

The first thing we need to do is change our mask to binary. If you do not know how to do this you should look at my other tutorial first which can be found Decimal to Binary


Now that you have converted your mask in to binary

224 = 11100000

Remember on a class C network the first 24 bits are owned by the network the last 8 bits are owned by the host.

So count the ammount of zero's "0" in the mask you will see there are 5 of them.

5 to the power of 2 = 32 - 2 = 30

So we have 30 hosts per subnet





Routers & Protocols

Routers and Protocols

The main service of a router is to provide or transmit data using layer 3 addresses. This is known as routing routing occurs at the network layer which is layer 3.

A wan operates at layer 1, 2, 3 so a router is both a WAN and a LAN. This is why it has a LAN and WAN interface.

Routers require an IOS the same way computers need an OS. Routers use routing protocols to determine the best path for packets. When a router is setup properly it provides:

Consistent end to end addressing,

Addresses that representnetwork topologies,

best path selection,

Dynamic and static routing,


Routing Protocols Description

Protocol suites are collections of protocols that enable hosts to communicate. Without protocols a computer can not rebuild the stream of incoming bits from another computer in to the original format.

Protocols control how the physical network is built, and how computers connect to the network.They control how data is formated for transmission & how it is sent. Protocols know how to deal with errors.

Bus Topology

A bus topology uses a single backbone cable that is terminated at both ends. All hosts on this network connect directly to this backbone.


Ring Topology

A ring topology connects one host to the next and the last to the first.


Star Topology

A start topology connects all cables to a central point


Hierarchiacal Topology

This is linked to a computer that controls all the traffic on the topology.


Mesh Topology

Each host has it's own connections to all other hosts


Extended Star Topology

This method links individual start together by connecting the hubs or switches


Logical Topology

The logial topology of a network determines how the hosts communicate across the medium. The two most common types of logical topology are broadcast and token passing


Broadcast Topology

This indicates that each host sends it's data to all other hosts on the network medium. There is no order to follow for these type of stations it is simply first come first server.


Token Passing

An electronic token is passed sequentially to each host, when a host receives the token that host can then send data on the network.



Cisco Default Routes


This page will describe default routes and explain how they are configured.

By default, routers learn paths to destinations three different ways:

Static routes – The system administrator manually defines the static routes as the next hop to a destination. Static routes are useful for security and traffic reduction, as no other route is known.

Default routes – The system administrator also manually defines default routes as the path to take when there is no known route to the destination. Default routes keep routing tables shorter. When an entry for a destination network does not exist in a routing table, the packet is sent to the default network.

Dynamic routes – Dynamic routing means that the router learns of paths to destinations by receiving periodic updates from other routers.


 The static route is indicated by the following command:

Router(config)#ip route

The ip default-network command establishes a default route in networks using dynamic routing protocols:

Router(config)#ip default-network

Generally after the routing table has been set to handle all the networks that must be configured, it is often useful to ensure that all other packets go to a specific location. This is called the default route for the router. One example is a router that connects to the Internet. All the packets that are not defined in the routing table will go to the nominated interface of the default router.

The ip default-network command is usually configured on the routers that connect to a router with a static default route. 

Hong Kong 2 and Hong Kong 3 would use Hong Kong 4 as the default gateway. Hong Kong 4 would use interface as its default gateway. Hong Kong 1 would route packets to the Internet for all internal hosts. To allow Hong Kong 1 to route these packets it is necessary to configure a default route as:

HongKong1(config)#ip route s0/0

The zeros in the IP address and mask portions of the command represent any destination network with any mask. Default routes are referred to as quad zero routes. In the diagram, the only way Hong Kong 1 can go to the Internet is through interface s0/0.



How many subnets 


If you are asked to work out a subnet mask that will supply a certain amount of subnets this is how you can do it.

Before you go any further it is best if you know how to convert binary in to decimal

In this example you are asked to create a mask for 10 subnets. This is quite easy as long as you understand the power of 2



So 2^ of what? makes the desired subnets, look at my chart above we have been asked to create a subnet that will cater for 10 subnets. So if we look at 2^3 this would give us 8 subnets this is not enough. So if we look at 2^4 this would give us 16 subnets this is plenty as we need 10.

So lets convert that to binary 2^4 so we are using 4 zero's and 4 one's

11110000 This binary number converts to 240 which is the last subnet in the mask.








Introduction to Wans

A WAN is a data communications network that spans a large geographic area such as a state, province, or country. WANs often use transmission facilities provided by common carriers such as telephone companies.
These are the major characteristics of WANs:

They connect devices that are separated by wide geographical areas.

They use the services of carriers such as the Regional Bell Operating Companies (RBOCs), Sprint, MCI, and VPM Internet Services, Inc. to establish the link or connection between sites.

They use serial connections of various types to access bandwidth over large geographic areas.


A WAN differs from a LAN in several ways. For example, unlike a LAN, which connects workstations, peripherals, terminals, and other devices in a single building, a WAN makes data connections across a broad geographic area. Companies use a WAN to connect various company sites so that information can be exchanged between distant offices.
A WAN operates at the physical layer and the data link layer of the OSI reference model. It interconnects LANs that are usually separated by large geographic areas. WANs provide for the exchange of data packets and frames between routers and switches and the LANs they support.
The following devices are used in WANs:

Routers offer many services, including internetworking and WAN interface ports.

Modems include interface voice-grade services, channel service units/digital service units (CSU/DSUs) that interface T1/E1 services, and Terminal Adapters/Network Termination 1 (TA/NT1s) that interface Integrated Services Digital Network (ISDN) services.

Communication servers concentrate dial in and dial out user communication.


The Interactive Media Activity will help students become more familiar with WAN devices.
WAN data link protocols describe how frames are carried between systems on a single data link.
They include protocols designed to operate over dedicated point-to-point, multipoint, and multi-access switched services such as Frame Relay. WAN standards are defined and managed by a number of recognized authorities, including the following agencies:

International Telecommunication Union-Telecommunication Standardization Sector (ITU-T), formerly the Consultative Committee for International Telegraph and Telephone (CCITT)

International Organization for Standardization (ISO)

Internet Engineering Task Force (IETF)

Electronic Industries Association (EIA)