Master Local Area Network (LAN) Topologies In Just A Few Hours!
Local Area Network (LAN) Topologies
Over the years, there has been experimentation and implementation of
various network designs. In reference to networking, when we refer to
the term "topology", we are actually referring to the design or look of the
network at hand. Let's discuss the advantages and disadvantages of these
topologies below. Master Local Area Network (LAN) Topologies In Just A Few Hours!
Ring Topology
The ring topology (also known as token topology) boasts some similarities. Devices such as computers are connected directly
to each other to form a loop, meaning that there is little cabling required
and less dependence on dedicated hardware such as within a star topology.
A ring topology works by sending data across the loop until it
reaches the destined device, using other devices along the loop to forward the
data. Interestingly, a device will only send received data from another device
in this topology if it does not have any to send itself. If the device happens
to have data to send, it will send its own data first before sending data from
another device.
Because there is only one direction for data to travel across this
topology, it is fairly easy to troubleshoot any faults that arise. However,
this is a double-edged sword because it isn't an efficient way of
data travelling across a network, as it may have to visit many
multiple devices first before reaching the intended device.
Lastly,
ring topologies are less prone to bottlenecks, such as within a bus
topology, as large amounts of traffic are not travelling across the network at
any one time. The design of this topology does, however, mean that a fault
such as cut cable, or broken device will result in the entire networking
breaking.
This lab will take you through the flaws in different network topologies
-
In a ring topology, all devices are a connector to two others to create a
full circle
-
Packets of data travel from one device to the next until they have reached
their destination
-
One of the major flaws with a ring topology is that if a device goes down or
a cable is broken, then data will no longer be passed
-
If you hover over the middle of the network cable, you can cut it and see
what happens to the packets
-
If you hover over the middle of the network cable, you can cut it and see
what happens to the packets
-
The packets can now no longer travel around the network, and no devices can
talk to each other
Bus Topology
This type of connection relies upon a
single connection which is known as a
backbone cable. This type of topology is similar to the leaf off
of a tree in the sense that devices (leaves) stem from where the branches are
on this cable.
Because all data destined for each device travels
along the same cable, it is very quickly prone to becoming slow and
bottlenecked if devices within the topology are simultaneously
requesting data. This bottleneck also results in very difficult
troubleshooting because it quickly becomes difficult to identify which device
is experiencing issues with data all travelling along the same route.
However, with this said, bus topologies are one of the
easier and more cost-efficient topologies to set up because of
their expenses, such as cabling or dedicated networking equipment used to
connect these devices.
Lastly, another disadvantage of the bus
topology is that there is little redundancy in place in case of failures. This
disadvantage is because there is a single point of failure along the backbone
cable. If this cable were to break, devices can no longer receive or transmit
data along the bus.
-
With a bus topology, all devices are connected to a single cable, often
called the backbone.
-
Data is sent in both left and right directions down the backbone until the
packet's destination is reached.
-
A major flaw in the bus topology is that it can't handle a large amount of
data.
-
On the next step, send as many packets as quickly as you can to try and
take down the network
Star Topology
The main premise of a star topology is that devices are
individually connected via a central networking device such as a switch or
hub. This topology is the most commonly found today because of its reliability
and scalability - despite the cost.
Any information
sent to a device in this topology is sent via the central device to which it
connects. Let's explore some of these
advantages and disadvantages of this
topology below:
Because more cabling & the purchase of dedicated networking
equipment is required for this topology, it is more expensive than any of the
other topologies. However, despite the added cost, this does provide some
significant advantages. For example, this topology is much more scalable in
nature, which means that it is very easy to add more devices as the demand for
the network increases.
Unfortunately, the more the network scales, the more maintenance is
required to keep the network functional. This increased dependence on
maintenance can also make troubleshooting faults much harder. Furthermore, the
star topology is still prone to failure - albeit reduced. For example, if the
centralised hardware that connects devices fails, these devices will no longer
be able to send or receive data. Thankfully, these centralised hardware
devices are often robust.
-
With a star topology, all devices are connected with their own cable to a
central switch/hub.
-
Every packet is sent through this switch, which means if the switch goes
down the network will no longer work.
- See if you can somehow break the switch.
What is a Switch?
Switches are dedicated devices within a network that are designed to
aggregate multiple other devices such as computers, printers, or any other
networking-capable device using ethernet. These various devices plug into a switch's port. Switches are usually found
in larger networks such as businesses, schools, or similar-sized networks,
where there are many devices to connect to the network. Switches can connect a
large number of devices by having ports of 4, 8, 16, 24, 32, and 64 for
devices to plug into.
Switches are much more efficient than their
lesser counterpart (hubs/repeaters). Switches keep track of what device is
connected to which port. This way, when they receive a packet, instead of
repeating that packet to every port like a hub would do, it just sends it to
the intended target, thus reducing network traffic.
Both Switches and Routers can be connected to one another. The ability to do
this increases the redundancy (the reliability) of a network by adding
multiple paths for data to take. If one path goes down, another can be used.
Whilst this may reduce the overall performance of a network because packets
have to take longer to travel, there is no downtime -- a small price to pay
considering the alternative.
What is a Router?
It's a router's job to connect networks and pass data between them. It
does this by using routing (hence the name router!).
Routing is the
label given to the process of data travelling across networks. Routing
involves creating a path between networks so that this data can be
successfully delivered.
Routing is useful when devices are
connected by many paths, such as in the example diagram below.
1) What does LAN stand for?
Ans - Local
Area Network
2) What is the verb given to the job that Routers perform?
Ans - Routing
3) What device is used to centrally connect multiple devices on the local
network and transmit data to the correct location?
Ans - Switch
4) What topology is cost-efficient to set up?
Ans - Bus Topology
5) What topology is expensive to set up and maintain?
Ans - Star Topology
A Primer on Subnetting
As we've previously discussed throughout the module so far, Networks can
be found in all shapes and sizes - ranging from small to large.
Subnetting is the term given to splitting up a network into
smaller, miniature networks within itself. Think of it as slicing up a cake
for your friends. There's only a certain amount of cake to go around, but
everybody wants a piece. Subnetting is you deciding who gets
what slice & reserving such a slice of this metaphorical cake.
Take
a business, for example; You will have different departments such as:
Accounting
Finance
Human
Resources
Whilst you know where to send information in
real life to the correct department, networks need to know as well.
Network administrators use subnetting to categorise and assign
specific parts of a network to reflect this.
Subnetting
is achieved by splitting up the number of hosts that can fit within the
network, represented by a number called a subnet mask. Let's refer back to our
diagram from the first room in this module:
As we can recall, an IP address is made up of four sections
called octets. The same goes for a subnet mask which is also represented as a
number of four bytes (32 bits), ranging from 0 to 255 (0-255).
Subnets use IP addresses in three different ways:
Identify the network address
Identify the host address
Identify the default
gateway
Let's split these three up to understand their purposes into
the table below:
|
Type
|
Purpose
|
Explanation
|
Example
|
|
Network Address
|
This address identifies the start of the actual network and is used to
identify a network's existence.
|
For example, a device with the IP address of 192.168.1.100 will be on
the network identified by 192.168.1.0
|
192.168.1.0
|
|
Host Address
|
An IP address here is used to identify a device on the subnet
|
For example, a device will have the network address of 192.168.1.1
|
192.168.1.100
|
|
Default Gateway
|
The default gateway address is a special address assigned to a device on
the network that is capable of sending information to another network.
|
Any data that needs to go to a device that isn't on the same network
(i.e. isn't on 192.168.1.0) will be sent to this device. These devices
can use any host address but usually use either the first or last host
address in a network (.1 or .254)
|
192.168.1.254
|
Now, in small networks such as at home, you will be on one subnet
as there is an unlikely chance that you need more than 254 devices connected at one time.
However, places such as businesses and offices will
have much more of these devices (PCs, printers, cameras and sensors), where subnetting takes place.
Subnetting provides a range of benefits, including:
Efficiency
Security
Full
control
We'll come on
to explore exactly how subnetting provides these benefits at a later date;
however, for now, all we need to understand is the security element to it.
Let's take the typical café on the street. This cafe will have two
networks:
One for employees, cash registers, and other
devices for the facility
One for the general public to use as a
hotspot
Subnetting allows you to separate these two use cases
from each other whilst having the benefits of a connection to larger networks
such as the Internet.
1) What is the technical term for dividing a network up into smaller
pieces?
Ans - Subnetting
2) How many bits are in a subnet mask?
Ans - 32
3) What is the range of a section (octet) of a subnet mask?
Ans - 0-255
4) What address is used to identify the start of a network?
Ans - Network address
5) What address is used to identify devices within a network?
Ans - Host address
6) What is the name used to identify the device responsible for sending
data to another network?
Ans - Default Gateway
Provided by Hacking Truth
The ARP Protocol
Recalling from our previous tasks that devices can have two identifiers:
A MAC address and an IP address, the ARP protocol or
Address Resolution Protocol for short, is the technology that is
responsible for allowing devices to identify themselves on a network.
Simply,
the ARP protocol allows a device to associate its MAC address with an IP
address on the network. Each device on a network will keep a log
of the MAC addresses associated with other devices.
When devices
wish to communicate with another, they will send a broadcast to
the entire network searching for the specific device. Devices can use the
ARP protocol to find the MAC address (and
therefore the physical identifier) of a device for communication.
How does ARP Work?
Each device within a network has a ledger to store information on, which
is called a cache. In the context of the ARP protocol, this cache stores the
identifiers of other devices on the network.
In order to map these two identifiers together (IP address and MAC
address), the ARP protocol sends two types of messages:
ARP Request
ARP
Reply
When an ARP request is sent, a
message is broadcasted to every other device found on a network by the device,
asking whether or not the device's MAC address matches the requested IP
address. If the device does have the requested IP address, an
ARP reply is returned to the initial device to acknowledge this.
The initial device will now remember this and store it within its cache (an
ARP entry).
This process is illustrated in the diagram
below:
1) What does ARP stand for?
Ans - Address
resolution protocol
2) What category of ARP Packet asks a device whether or not it has a
specific IP address?
Ans - Request
3) What address is used as a physical identifier for a device on a
network?
Ans - MAC Address
4) What address is used as a logical identifier for a device on a
network?
Ans - IP address
The DHCP Protocol
IP addresses can be assigned either manually, by entering them
physically into a device, or automatically and most commonly by using a DHCP
(Dynamic Host Configuration Protocol) server. When a device connects to a network, if it has not already been
manually assigned an IP address, it sends out a request (DHCP Discover) to see
if any DHCP servers are on the network. The DHCP server then
replies back with an IP address the device could use (DHCP Offer). The device then sends a reply confirming it wants the offered IP Address
(DHCP Request), and then lastly, the
DHCP server sends a reply acknowledging this has been completed, and the device can start using the IP Address (DHCP
ACK).
1) What type of DHCP packet is used by a device to retrieve an IP
address?
Ans - DHCP Discover
2) What type of DHCP packet does a device send once it has been offered an
IP address by the DHCP server?
Ans - DHCP Request
3) Finally, what is the last DHCP packet that is sent to a device from a
DHCP server?
Ans - DHCP Ack
Provided by Hacking Truth
Disclaimer
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