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Network Basics

Network components

What comprises our networks :

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Network Basics

Network Geography

PAN

The Personal Area Network (PAN) is the smallest type of wired or wireless network and covers the least amount of area. (ex : usb & bluetooth)

LAN

The Local Area Network (LAN) connects components within a limited distance. (generally up to 100 meters or 300 feet)

Your network can be consisting of either wifi or eithernet. If using ethernet, you're going to use the IEEE 802.3 standard.

If using wifi, you're going to use the IEEE 802.11 standard.

CAN

The Campus Area Network (CAN) connects LANs that are building-centric across a university, industrial park, or business park. This can cover several miles, and across many different buildings.

OSI Model

OSI Model Overview

Intro

The Open System Interconnection model (OSI) was developed in 1977 by the International Organization for Standardization. This orgnization is responsible for creating different standards, which we refer to to as the ISO. For example, if you see ISO 7498, that's the standard we use to refer to the OSI model.

Networks are all about communicating data. Data is going to be called different things as it flows through our network it goes through different names as it goes through those different layers of the OSI model.

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The OSI model starts at the Physical Layer and ends at the Application Layer. When we talk about data at layers 7, 6, 5 we are talking about information. At layer 4 (transport layer) we're going to call data a segment. At layer 3 (network layer) we refer to it as a packet. At layer 2 (data link layer) we call it a frame. At layer 1 (physical layer) is where you've convererted the data into 1s & 0s to send it across our medium (wire), we call this bits.

Layer 1 (Physical Layer)

Intro

At the bottom of the OSI Model is we'll we find our first layer, the physical layer. This is where bits are transmitted across the network and includes all of the physical and elecetrical characteristics of this network. This is going to tell us whether we're using an Ethernet network, whether we're using fiber or copper cables, whether we're using Cat5 or Cat6, and even if we're using radio frequency in the case of Wi-Fi.

Bits

Regardless of which method we're using to send our data across this first layer, it's always going to occur as binary bits. These are going to be a series of 1s & 0s. Now, each media has a different way of representing thse bits, these series of 1s & 0s, because these series of 1s & 0s are the basic building blocks of all of our data. Now, when we switch between these two modes, whether we should read a 1 or a 0 on the network, this is called transition modulation. Data on a computer network is represented as a binary expression. Electrical voltage (on copper wiring) or light (carried via fiber-optic cabling) can represent these 1s and 0s. The presence or the absence of voltage on a wire can represent a binary 1 or a binary 0, respectively. The presence or absence of light on a fiber-optic cable can represent a 1 or 0 in binary.

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Wiring

As we start understanding that, we then haveto look at the cables themself becuase this is also part of our physical layer. If we're using someting like a Cat5 or a Cat6 cable, we may have a certain connector on the end called an RJ45, which allows us to plug that cable into the back of a computer or into a switch. The way that connector is wired is based on a certain standard. We use two standards inside our network: TIA/EIA-568A and TIA/EIA-568B. Now, we'll talk about these and which way these pins actually are set up inside, this connector in a future lesson.

Topology

There's on thing we have to think about at the physical layer, and that's the topology of the network. How are we actually running these cables to physically connect the different decices together?

We can look at this from a Layer 1 perspective. Is it a bus, it it a ring, is it a star? Is it a hub and spoke? How about a full mesh, a partial mesh, or any other topology that we discussed. When it comes to figuiring this out, your're going to look at how they're physically cabled, and if you drew them out, that will tell you what phyiscal topology you have.

Synchronizing bits

For two networked devices to successfully communicate at the physical layer, they must agree on when 1 bit stops and another bit starts. Two basic approaches to bit synchronization include asynchronous & synchronous.

With the asynchronous bit synchronization approach, a sender indicates that it is about to start transmitting by sending a start bit to the receiver. When the receiver sees this, it starts its own internal clock to measure the subsequent bits. After the sender transmits its data, it sends a stop bit to indicate that it has finished its transmission.

With the synchronous bit synchronization approach, it synchronizes the internal clocks of both the sender and the receiver to ensure that they agree on when bits begin and end. A common approach to make this synchronization happen is to use an external clock (for example, a clock provided by a service provider), which is referenced by both the sender and the receiver.

Bandwidth usage

Speed is measured by the total amount of data you can download or upload in one second. Bandwidth is measured by the total amount of data you’re allowed to download or upload in one second, which depends on your internet plan and the connection type. Bandwidth is your maximum possible speed.

The two fundamental approaches to bandwidth usage on a network are broadband and baseband.

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Baseband is a system that uses a single data channel in which the whole bandwidth of the transmission medium is dedicated to one data channel at a time. Baseband uses all of the frequency of the cable all of the time. An example of this is a telephone, because picking up the phone uses all of the bandwidth allocated to that phone line. Another example of baseband network is a wired home thernet network.

When we use baseband, we're use a reference clock that allows us to send the information for both the sender and receiver at the certain time. By using this reference clock, this is an example of using a synchronous communication.

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Broadband is a multiple data channel system in which the bandwidth of the transmission medium carries several data streams at the same time. Broadband is going to divide our bandwidth into seperate channels. An example of this is a TV service because a single cable is coming into your home, but it carries 200+ channels.

In summary baseband is related to digital signals, while broadband is related to analog signals. Baseband system does not allow digital signals to share one medium simultaneously while broadband system can transmit different data side by side at the same time.

Multiplexing

Multiplexing is a technique in wihch several signals are combined into one composite signal so that they can all be transmitted on a common channel. In order to transmit various signals in a single common channel, it is important to keep them seperated as to not cause interference and to make it possible for the receiving end to seperate them.

Time-division multiplexing (TDM) supports different communication sessions on the same physical medium by causing the sessions to take turns. For a brief period of time, defined as a time slot, data from the first session will be sent, followed by data from the second session. This continues until all sessions have had a turn, and the process repeats itself.

A downside to TDMis that each communication session receives its own time slot, even if one of the sessions does not have any data to transmit at the moment. To make a more efficient use of available bandwidth, Statistical time-division multiplexing(StatTDM) dynamically assigns time slots to communications sessions on an as-needed basis.

Frequency-division multiplexing FDM divides a medium’s frequency range into channels, and different communication sessions transmit their data over different channels.

Now, for the exam, the good news is you don't need to memorize TDM, StatTDM, and FDM, but rather you just need to understand that multiplexing involves taking some limited amount of resource and using it more efficiently. Multiplexing allows multiple people to use a baseband connection at the same time

Physical Layer Device Examples

The final thing we need to talk about is some examples of Physical/Layer1 devies. The most common one is a cable. If I have a fiber optic cable or an Ethernet cable or a coaxial cable, these are all different types of media. So, if I have a fiber optic cable and I put light in one end, I'm going to get light out of the other end. That's a physical response, a physical layer of the OSI Model.

Additionally, beyond wired cables, we also have wireless things, things like Bluetooth and Wi-Fi and near field communication. All of these radio frequencies make up the media at Layer1 for those types of networks.

The final example is infrastructure devices, and that will be things like hubs, access points, and media converters. All of these devices operate at the bit layer. This is going to be a function to just simply repeat what they get.

Whatever comes in is gonig to go out. There's no logic to it, there's no intelligence to it. Layer1 devies simply repeat whetever they're told. Later1 is dumb devices. They're simply repeaters. Whatever they take in, they sind it right back out.

Layer 2 (Data-Link Layer)

Intro

The Layer 2 of the OSI model, the data link layer. In the data link layer we're going to package up bits from Layer 1 and put those into frames and then, we're going to take frames and transmit them throughout the network while performing some error detection detection, correction, identifying unique network devices using MAC addresses, and we're going to provide some flow control. With Layer 2 we deal with things on a logical level.

MAC address

A MAC address (media access control address) is a means for identifying a device physically and allowing it to operate on a logical topology. These MAC addresses are important for dealing with switches and other Layer 2 devices.

When it comes to identifying MAC addresses, every manufacturer of a network card assigns a unique 48-bit physical adressing system to every network interface card they produce. A 12-digit hexadecimal number is used to represent MAC addresses. MAC addresses are always written hexadecimally wherein each of the letter or numbers is considered four bits.

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The first 24 bits or six letters/numbers as you can see here identifies the particular vendor who made that card. The second half is going to represent the exact machine it belongs to.

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LLC Layer

The data link layer is the second lowest layer. It is divided into two sublayers. The logical link control (LLC) sublayer, and (MAC) sublayer.

Logical Link Control (LLC) provides connection services and allow your recipients to acknowledge the messages have gotten where you thought thought they were going. LLC is the most basic form of flow control, essentially it's going to limit the amount of data that a sender can send at once and allow the receiver to keep from being overwhelmed.

LLC also provices basic error control functions such as allowing the receiver to inform the sender if their data fram wasn't received, or if it was received corrupted and it does this by using a checksum. Since everything it receives is just a series of 1s & 0s, the receiver is going to add all of these up and the last bit will either be even or odd. If it matches, they add them all up and if they're even, then, it's going to assume that this was good. If you have received a zero that means it was even. If the last bit was oddi>, meaning it was a one, and they added up all the numbers and they got an odd number, that means it was good, as well. But if not, they can figure that something was bad and then ask for a retransmission of the frame.

??? The primary function of LLC is to multiplex protocols over the MAC layer while transmitting and likewise to de-multiplex the protocols while receiving. LLC provides hop-to-hop flow and error control. It allows multipoint communication over computer network. Frame Sequence Numbers are assigned by LLC. In case of acknowledged services, it tracks acknowledgements

How is communication synchronized?

Communication can be synchronized across Layer 2 according to three different schemes.

First we have something known as isochronous mode which happens when the networks use a common reference clock similar to synchronous, yet they also crate time slots for transmissions, much like we did with time division multiplexing. This has less overhead than either of the other two modes because both devices know when they can communicate and for exactly how long.

The second method we can use is known as synchronous method and this is much like Layer 1. It's going to involve devices using the same clock. But the reason it's different from isochronous is that this is going to allow us to have beginning and ending frames and and special control characters to tell us when we're going to start and when we're going to end based on those beats. Networks operate in that devices can only communicate at frequencies specified by particular clock cycles. Because of this, there isn't a lof of gap time that isn't already properly utilized and this becomes a major drawback for sychronized mode.

Finally we have asynchronous which is going to allow each of our network decives to reference their own clock cycles and use their own clock cycles and their own start and stop bits. In this way, there's no real control over when the devices are allowed to communicate, and that becomes the major drawback here.

Ending?

Now, when we look at Layer 2 devices, we have things like network interface cards, bridges, and switches. In contrast to how a hub is a dumb machine that simply relies on a message coming in and repeating it back out, switches are smarter. They can actually use logic to learn which physical ports are attached to which devices based on their MAC addresses. This way they can send data to specific devices in the network, allowing us to picm up and choose different lines of communication to go to different areas.

?! Now, we'll talk all about how this works and how these switches do these including things like CAM tables using the MAC addresses and how they're doing the switching across the network in later lessons and we'll go into depth in that because you will need to understand that to understand how networks really work. But for right now, just remember that switches, bridges, and MAC addresses are three great examples of things that operate at Layer 2, the data link layer.

Layer 3 (Network Layer)

Intro

At the network layer, we're concerned with routing. Layer 3 is all about how we're going to foward traffic, which we refer to as routing uisng logical addresses.

For example, your computer has an IP address. And that IP adress is either going to be an IP version 4 (IPv4) or an IP version 6 adress (IPv6), or both. Both of these are considered Layer 3 protocols IPv4, and IPv6 are the most common and popular logical addressing scheme

We're also going to be concerned with what's known as switching, also known as routing. Not to be confused with switches which are layer 2 devices.

Upcoming concepts :
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IP address

Back in the '80s and '90s, there was AppleTalk for Apple computers. And if you used a Windows or a Novell Network computer, you might have used IPX, which was the Internetwork Packet Exchange. What killed both these off was Internet Protocol (IP) There are other protocols that you could use in Layer 3, IP is just the most common.

Now, some of those are still existing on some legacy systems, which means old systems in some corporate network. The routing protocol of the internet that we use today is known as IP. Recall IP comes in two variants, IPv4 and IPv6.

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Above is an example of an IP address This is called a dotted-octet notation which is four sets of numbers separated by dots.

How should data be forwarded or routed?

There are three main ways for data to be forwarded or routed. Which are Packet switching, Circuit switching, Message switching.

The most commonly used on in a network is going to be routing, which is also known as packet switching. This is where data is divided into packets and then forwarded on based on it's IP address. Packets are going to take different routes, and we don't care which route it takes, as long as it gets to its final destination.

When we talk about circuit switching, though, this where we want to have the same path each and every time. We're going to get a dedicated communications link that's established between our two devices.

Now the third type of switching we have is known as message switching. This is where all the data is divided into messages, and they're similar to packet switching in this idea but the messages can actually be stores and forwarded. We want to make sure the data is going to get where it's going, and that's why message switching can be very for us.

Almost all of our networks nowadays and the ones you utilize are going to be using packet switching. The reason is we have other methods that will check if something is not getting to the distant end, and will be resent over another path until it finally gets there. Most of the Internet works by using packet switching.

Route discovery and selection

Next is route discovery and selection this is how are we going to decide which path we're going to take to send a message. Routers maintain a routing table so, they can understand how to forward a packet based on the destination IP of where it wants to get to.

There are lots of different ways that it can do this, and they can do this either as a static route, or a dynamically-assigned route using a routing protocol like RIP, OSPF, & EIGRP. Routing protocols help us decide how data is going to flow across the network, and how the routers are going to communicate that information.

Connection Services

Connection services are going to augment layer 2 connection services and provide us with some additional reliability. Again, we're going to have some flow control added here, and this is going to prevent the sender from sending data faster than the receiver can get it.

We also have packet reordering. This is really important because it allows us to take a big chunk of data, cut it up into little pieces of packets, and then send all those packets off in different directions to get to their final destination. A problem that usually arises is that packets arrive at the destination in the wrong order. Packet reordering allows them to get all this data at the end destination at the receiver. The benefit here is that because of routing, each packet gets numbered and sequenced, and we can put them back into the right order.

Internet Control Message Protocol (ICMP)

Internet Control Message Protocol (ICMP) is is used to send messages and operational information to an IP destination. The most commonly used one is ping. Ping sends out a packet and tells us if it was received or not by the distant end and how long it took. This is not a tool used regularly by end-user applications, but it is used by us as adminstrators to help troubleshoot our network.

Another variation is known as traceroute, which will trace thr route that a packet takes through the network and tells you every single router along the way as it goes through.

Layer 3 devices

Now lets look at some layer 3 devices that we need to remember for the exam. The first two are routers, and multilayer switches.

A router looks like this icon below, a circle with four arrows. This is a depiction of what a router looks like in a logical diagram.

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A multilayer switch works like a switch, and router combined. It has both features of a layer 2 switch, and a layer 3 router. Remember that a switch is always a layer 2 device, unless it's a multilayer switch, which will then be a layer 3 device.

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Layer 4 (Transport Layer)

Lower/Upper layers

At layer 4 we have the transport layer. Now, the transport layer is our dividing line between what we call the upper layers of the OSI model and the lower layers of the OSI model.

Now the lower layers consist of physical, data link, & network layers. While the upper layers consist of transport, session, presentation, & application layer.

TCP & UDP protocols

Transmission control protocol (TCP) is a connection oriented protocol is a reliable way to transport segments across our network. Now, if a segment has dropped, the protocol will ask for acknowledgment each and every time. If it doesn't get that acknowledgement, it's going to resend that piece of information. For this reason we call is a connection full protocol, because it has this two-way type of information.

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Now, let's look at the diagram above. Here we have a client on the left, and a server on the right. The client is going to send what's called a synchronization packet (SYN packet)

Three-way handshake

Now this is what refer to as a three-way handshake.

TCP/IP Model

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Data Transfer Over Networks

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Ports and Protocols

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Finding Open Ports

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IP Protocol Types

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Media and Cabling Distribution

Media and Cabling

Copper Media

Building a Cable

Fiber Media

Transceivers

Cable Distribution

Wiring a Network

Testing the Network

Ethernet Fundamentals

Network Infrastructure Devices

Hands-on with Devices

Additional Ethernet Switch Features

Spanning Tree Protocol

Virtual Local Area Network (VLAN)

Specialized Network Devices

Other Devices

IP Addressing

IPv4 Addressing

IPv4 Data Flows

Assigning IP Addresses

Computer Mathematics

Subnetting

Subnetting Practice

Subnetting by Hand

IPv6 Addressing

IPv6 Data Flows

Routing

Routing Fundamentals

Routing Tables

Routing Protocols

Address Translation (NAT and PAT)

Multicast Routing

Network Services

DHCP

Hands-on with DHCP

DNS

Hands-on with DNS

NTP

Wide Area Networks (WANs)

Wide Area Networks (WAN)

Wired WAN Connections

Wireless WAN Connections

WAN Technologies (Part 1)

WAN Technologies (Part 2)

Hands-on with WANs

Other WAN Connections

Wireless Networks

Wireless Networking (WLAN)

WLAN Service Sets

Wireless Antennas

Hands-on- with Antennas

Wireless Frequencies

Wireless Security

Hands-on with Wireless

When Security Fails

Cloud and the Datacenter

Virtual Network Devices

Voice Over IP (VoIP)

Cloud Computing

Cloud Concepts

Virtualization and Cloud Computing

Infrastructure as Code

Connectivity Options

Datacenter Architecture

Network Security

The CIA Triad

Threats and Vulnerabilities

Risk Management

Security Principles

Defense in Depth

Multifactor Authentication

Authentication Methods

Network Access Protocols

Network Access Control

Physical Security

Asset Disposal

Network Attacks

Denial of Service Attacks

General Network Attacks

Spoofing Attacks

Malware

Security Technologies

Firewalls

Hands-on with Firewalls

Hands-on with Software Firewalls

IDS and IPS

Remote Access

Virtual Private Networks (VPNs)

IPSec

Simple Network Management Protocol

Network Logging

SIEM

Networking Hardening

Network Hardening

Patch Management

Password Security

Unneeded Services

Port Security and VLANs

Inspection and Policing

Securing SNMP

Access Control Lists

Wireless Secuirty

loT Considerations

Network Availability

Networking Avaliablity

High Availability

Designing Redundant Networks

Recovery Sites

Facilities Support

Quality of Service (QoS)

Qos Categorization

QoS Mechanisms

Network Policies

Plans and Procedures

Hardening and Security Policies

Common Agreements

Network Management

Common Documentation

Performance Metrics

Sensors

NetFlow Data

Interface Statistics

Environmental Sensors

Troubleshootin Physical Networks

Network Troubleshooting Methdology

Cable Review

Cabling Tools

Cable Signal Issues

Copper Cable Issues

Fiber Cable Issues

Ethernet Issues

Troubleshooting Wireless Networks

Wireless Considerations

Coverage and Interference

Incorrect Configurations

Captive Portal

Network Tools and Commands

Software Tools

ping and traceroute

ipconfig, ifconfig, and ip

nslookup, dig, and hostname

arp, route, nbtstat, netstat

telnet, tcpdump, and nmap

Troubleshooting Network Issues

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Collisions and Broadcast Storms

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Duplicate Addresses

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Routing Issues

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Loops

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DHCP Issues

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IP and VLAN Settings

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Firewall Issues

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DNS and NTP Issues

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Network Performance Issues

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Other Issues

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Network Devices

Network Devices Part 1

Host

Host are any device which sends or receive traffic. (Examples : Computers, Phones, smart TVs, smart watches, etc)

Host typically fall in two categories clients or servers. Clients initiate request servers respond. These terms are relative to specific communication. (A server is a computer with software installed which responds to specific request)

IP Address

An IP Address is the identity of each host. An IP address is needed to send or receieve packets on a network. IP addresses get stamped on everything that each host sends.

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For example when a client makes a web request to site.com, it sends a packet which includes what web page it is asking for, as well as a source ip address, and a destination ip addresses.

The source ip address is going to be the client's ip address, and the destination ip address is going to be the server's ip address.

IP addresses are typically assigned in some sort of hierachy.

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Network

A network is what actually does the transportation of traffic between hosts. In it's simplest form anytime you connect two hosts you have a network.

Before networks in order to transfer data between hosts required portable media (disks, thumb drives, etc...).

A network is really just a logical grouping of hosts which require similar connectivity. Networks can contain other networks which is reffered to as Sub-Networks (Subnets).

Instead of having networks connect directly to each other in every possible combination, networks are connected to a central resource, the internet which is simply a bunch of interconnected networks, networks connected to other networks.

Network Devices Part 2

Repeater?

Repeaters regenerate signals

Hub

Hubs are multiport repeaters.

Bridge

Bridges sit between HUB connected hosts.

Switch

A switch facilitates communication within a network.

Routers

A switch facilitates communication between a networks.

Gateway

A gateway is each hosts way out of their network.

OSI model

Intro

The purpose of networking is to allow two hosts to share data with one another. Networking allows us to automate all this across the wire. Hosts must follow a set of rules in order to achive this. Networking also has its own set of rules, the rules for networking are divided into seven different layers known as the OSI model.

OSI is simply a model, NOT RIGID.

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1) Physical ; Transporting bits ; Cables, Wifi, Repeaters, & Hubs
2) Data Link ; Hop to hop ; NIC, MAC Address, Routers, Switch
3) Network ; End to end ; IP Address
4) Transport ; Service to Service ; Two common address schemes to distinguish dates streams are TCP & UDP which are ports. TCP favors reliability. UDP favots efficiency. Port #s range from 0-65535.

Servers listen for request to pre-defined ports. Clients make request to the IP address & to the port # in question. Clients also select a random source port for each connection.

When a packet is initially send from a client it includes a Source (SRC) & Destination (DST)

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??This process occurs for each connection made the client the client. In each case the client is searching a new random source port.

Ports ensure that the right application gets the right data. THis process also allows the client to make multiple connections to the sme server. (exp : when client/browser opens a new tab, a new random source port is created.)

?Encapsulation

?The construct of a L2 header & its ensuing data is known as a frame.

Physical Layer

Everything Hosts do to speak on the Internet Pt1

Everything Switches do to speak on the Internet Pt1

Everything Routers do to speak on the Internet Pt1

Intro

.xxx (IP address)
.xxx (MAC address)

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Switches facilitates communication within a network(review). A node is a device the implements IP. A router is a node that forwards IP packets not explicitly to itself. A host is any node that is not a router.

A router forwards packets not destined to themselves. Routers are connected to a network by having an IP & MAC address on each interface (network). To do this routers must have a routing table corrilating to each route in each network. Each route has its own routing table.

Routers use the routing tables to send packets. Routing tables can be populated via 3 methods ; Directly Connected, Static Routes, & Dynamic Routers.

Directly connected are routes for the Network which are attached. When routes receive packets with an unknown destination IP, packet is dropped.

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Static routes are routes manually provided by an administrator.

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Everything Routers do to speak on the Internet Pt2

Intro

ARP is the mapping of known IP address to unknown MAC address. Routers have ARP Tables, mapping of L3 to L2 address. (Everying with an IP address has an ARP Table)

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ARP Tables start empty & get populated dynamically as needed with network traffic.

How packets are sent? (HostA -> HostC)

How hosts respond (HostC -> HostA)

Routing Hierachies & Route Summary

Intro

Routers are typically connected in a hierachy. Hierachy routers are easier to scale and allow for route summarization

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Subnetting

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A default route is the ultimate route.

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