Quick IP Cheat Sheet used for Reference

IP Cheat Sheet

	Hosts	Netmask	Amount of a Class C
/30	4	255.255.255.252	1/64
/29	8	255.255.255.248	1/32
/28	16	255.255.255.240	1/16
/27	32	255.255.255.224	1/8
/26	64	255.255.255.192	1/4
/25	128	255.255.255.128	1/2
/24	256	255.255.255.0	1
/23	512	255.255.254.0	2
/22	1024	255.255.252.0	4
/21	2048	255.255.248.0	8
/20	4096	255.255.240.0	16
/19	8192	255.255.224.0	32
/18	16384	255.255.192.0	64
/17	32768	255.255.128.0	128
/16	65536	255.255.0.0	256

How Computer Networking Can Benefit a Company

Technology is advancing at a rapid pace in today’s world. Businesses are constantly in high demands of technicians that understand the ebb and flow of information through technical devices and that is able to keep up with the growth and new innovations of demanding vendors. Computer networking is one of the many and perhaps most efficient way that information enters and leaves in the complex world of business.
Like any profession, computer networking is an art and science combined. A graphic designer can strike up a beautiful piece of artwork, but like any artist, whether it be a musician or the next Picasso, passionate artists can capture your emotions or attention. Most of the time, find themselves lost in the zone of their passion. This can be applied to computer networking as well, understanding how a business actually functions and fluctuates from day to day, month to month, and year to year is the first step in determining how to set up a network that is suitable for it. Through planning and drafting sketches, you can produce the best possible routing table and in the process, while keeping in mind how your vendor will use information, you can locate and weed out any possible conflicts or problems you may encounter in setting up this beautiful piece of network master piece. Combined with science and the results are unlimited, that’s why there are many more networking schemes to yet be discovered.
Like chemistry and biology, scientists are still researching on new medicines and cures for existing illnesses and diseases. For example, AIDS and HIV are one of the many researches taking place as one speaks. There are many computer scientists today, researching and developing new innovations in the lab and then test running them on current existing businesses to gain feedback and insights on the next big networking scheme. When implemented correctly, businesses can function properly with information being delivered on time, efficiently, and consistently; most definitely contributing to the success of a business and at the same time, giving them the upper hand in competition. We all know
that when things run smoothly, we can channel our focus on something else; in this case, the ROI of a business. So not only does efficient networking contribute to a business success, it allows it to direct its focus elsewhere, for example; push on sales and focus on net profit for a better return on investment and performance inclination. These are just a few major benefits businesses can gain through use of computer networking; it’s no wonder they spend millions of dollars for technology every year. Take Microsoft Sharepoint for example, last year alone, they spent over millions of dollars on innovations but made over hundreds of millions of dollars back on their returns of investments and profits. Sharepoint, a web-development platform has really proved indispensible to any business owner or business in need of a quick, professional, and functional website. About 5 years ago and the years preceding, you had to fully understand computer language, such as HTML, CSS, JavaScripts, and PHP to create a website Now, you just do it with the dragging and click of a button. Most likely, not as easy as 1, 2, 3, but it’s almost as easy as coloring a book. Although this may prove negatively on current professional designers, it has proved indispensible to businesses around the world, and that’s what new innovations ought to do; make life easier. It has also made the job a lot easier and reduced the cost of spending for website designers to most companies. One can reckon the force of how powerful technology can be, but at the same time how dangerous it could be to society.
In health and pharmaceuticals research, some corrupted scientist could invent a dose of drug that could be harmful or detrimental to society, or in the worst case scenario, wipe out the human population. Computer scientist must always be aware that an innovation of theirs could possibly be the vice versa outcome they had expected. This is where the movies and films such as iRobot and Frankenstein came about. Like all professions, good morals and values is essential to every step in research and development, let alone, life itself.
The ebb and flow of information isn’t just the presence and absence of information. It’s art and science combined, whether complex or compound, its value is crucial and vital on businesses all around the globe. For some it could mean a lot of money, but for the ones that truly have a passion in it, nothing is impossible. It’s the boundary between science and art, like the law of time, gravity, and the universe according to Albert Einstein. Time can only tell, but when solved, cracked, or broken; possibilities and new innovations are endless. For the time being though, they are just floating around, patiently waiting to yet to be discovered by a passionate artist/scientist.

Exam Essential: Internetworking

Know the possible causes of LAN traffic congestion
Too many hosts in a broadcast domain/storms, multicasting, and low bandwidth are all possible suspects of LAN traffic congestion.

Be able to distinguish the difference between a collision domain and a broadcast domain
Collision domain is an Ethernet term used to describe a network collection of devices in which one particular device sends a packet on a network segment, forcing every other device on that same segment to pay attention to it. On a broadcast domain, a set of all devices on a network segment hear all broadcasts sent on that segment.

Be able to distinguish the difference between a hub, a bridge, a switch, and a router
Hubs create one collision domain and one broadcast domain. Bridges break up collision domains but create one super duper large broadcast domain through use of hardware addresses to filter the network. Switches are really just multiple port bridges with more intelligence. They break up collision domains but create one large broadcast domain by default and also uses hardware addresses to filter the network. Routers break up broadcast domains (as well as collision domains) and use logical addressing to filter the network.

Know the OSI layers
It’s mandatory that you know the OSI layers and the function each layer provides. There are seven layers in the OSI reference model. The upper layers consist of The Application, Presentation, and Session Layers, and are responsible for communicating from a user interface to an application. The bottom layers consist of The Transport, Network, Data Link, and Physical Layers. The transport layer provides for segmentation, sequencing, and virtual circuits. The network layer provides for framing and placing of data on the network medium. Last but not least, the physical layer is responsible for taking 1s and 0s and encoding them into a digital signal for transmission on the network segment.

Remember the types of Ethernet cabling and when to use them
There are three types of cables that can be created from an Ethernet cable:

• Straight-through
• to connect a PC’s or a router’s Ethernet interface to a hub or switch.
• Crossover
• to connect hub to hub, hub to switch, switch to switch, or PC to PC.
• Rolled
• for a console connection from a PC to a router or switch

Understand how to connect a console cable from a PC to a router and commence HyperTerminal
You should know how to do this for the exam: Take a rolled cable and connect it from the COM port of the host to the console port of a router. Start HyperTerminal and set the BPS to 9600 and flow control to none.

Memorize the three layers in the Cisco three-layer model

• Core
• Distribution
• Access

Where do you take the CCNA Exams?

You can take the CCNA Composite exam at any Pearson VUE authorized testing centers or call 877-404-EXAM (3926).

Follow these steps to register for a CCNA exam:

1. Determine the number of exam you would like to take. (Composite exam number is 640-802.)
2. Register with the nearest Pearson VUE testing center. At this time, you will be asked to pay in advance for the exam. The current fee for the exam is $150.00 and must be taken within one year of the time of payment. You may also schedule exams up to six weeks in advance or as late as the day you are planning to take it on. However, if you fail a Cisco exam, you must wait five days before you are allowed to re-schedule for another shot at it. Because life can be unexpected, if something is to pop up on your test day, and you need to cancel or reschedule your exam, contact Prometric or Pearson VUE AT LEAST 24 hours in advance.
3. Upon scheduling the exam, you will receive instructions regarding all appointment and cancelation procedures, the ID requirements, and information regarding the testing-center location.

Here are some general tips for exam day:

1. Of course, arrive early at the exam location, so you’re able to relax and get a review in before the test. You should not be trying to study the information on this day.
2. Read each of the questions carefully. Be certain of what exactly each question is asking before diving in to conclusion.
3. If you’re stuck on a question, your best bet is to use the process of elimination to get rid of the obviously incorrect answers first. This can greatly improve your odds of choosing the wrong answer.
4. Because you can no longer move forward or backward through the exams, you will need to double-check your answers before proceeding to the next. Make sure you don’t forget this.
5. And last but not least, stay focused, attentive, and conscious throughout the whole exam.

The physical layer, hubs, and ethernet

The main functions of the physical layer is to send bits and receive bits, as well as state transitions.

• Bits come in only values of 1 or 0 (morse code with numerical values).
• State transitions – changes in voltage from high to low and vice-versa.

Hubs at the physical layer

What is a hub?

• A hub is really a multiple port repeater.

Hubs in a network

• All devices in the same collision domain.
• All devices in the same broadcast domain.
• Devices shares some bandwidth.

What is a Physical Star Network?

• A physical star network is where the hub is a central device and cables are extended in all directions from it.

Note: Hubs and repeaters can be used to enlarge the area covered by a single LAN segment, however, this is NOT RECOMMENDED.

Ethernet at the physical layer

• Created by a group called DIX (Digital, Intel, Xerox)
• There are three types of ethernet
  • 802.3u – Fast Ethernet
  • 802.3ab – Gigabit Ethernet on Category 5
  • 802.3ae – 10Gbps over fiber and coax

Electronics Industries Association and The Newer Telecommunications Industry Alliance (EIA/TIA)

• The standard body that creates the physical layer/specifications for ethernet.
• EIA/TIA specifies that ethernet use a registered jack (RJ) connector with a 4 5 wiring sequence on unshielded twisted pair (UTP) cabling (RJ45).

Cables

• Cables are measured in decibals (dB)
• Cabling in corporate and home markets is measured in categories.
  • A higher quality cable will have a higher rated category and lower attenuation.
    • ex. category 5 > category 3

Key term:

• Crosstalk – the unwanted signal interference from adjacent pairs in the cable.

A closer look at the Data-Link layer

The Data-Link layer provides physical transmission of the data and handles error notifications, network topology, and flow control.

Lets take a closer look at it’s function

1. Ensures messages are delivered to the proper device on LAN using hardware addresses and will translate messages from the Network layer to transmit.
2. Transmit messages into pieces called a data frame and adds a customized header containing the hardware destination and source address.
3. Data-Link uses binary values and hexadecimal values.

Binary Values

Nibble Values	Byte Values
8  4  2  1	128  64  32  16  8  4  2  1

Binary to Decimal Chart

Binary Value	Decimal Value
10000000	128
11000000	192
11100000	224
11110000	240
11111000	248
11111100	252
11111110	254
11111111	255

Hexadecimals

Hex is short for hexadecimal, which is a numbering system that uses the first six letters of the alphabet (A through F) to extend beyond the available ten digits in the decimal system. Hexadecimal has a total of sixteen digits.

Hex to Binary to Decimal Chart

Hexadecimal	Binary	Decimal
0	0000	0
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
A	1010	10
B	1011	11
C	1100	12
D	1101	13
E	1110	14
F	1111	15

Six major points of Routers

There are six major points to remember or keep in mind when working with routers or layer 3 devices. You should probably commit these to memory.

Here are the six major points

1. Routers, by default, will not forward any broadcast or multi-task packets.
2. Routers use the logical address in the network layer header to determine the next hop router to forward the packet to.
3. Routers can use access list, created by an administrator to control security on the types of packets that are allowed to enter or exit an interface.
4. Routers can provide layer 2 bridging functions if needed, and can simultaneously route through the same interface.
5. Routers provide connections between virtual LANS (VLANS).
6. Routers provide Quality of Service (QoS) for specific types of network traffic.

A closer look at the Network Layer

The network layer manages devices addressing, tracks location of devices on the network, and determines the best way to move data, which means the Network layer must transport traffic between devices that aren’t locally attached.

Lets take a closer look at it’s function

1. Checks a packet when it is first received on a router interface.
2. If the packet isn’t destined for that particular router, it will look up the destination network address in the routing table.
3. Once the router chooses an exit interface, the packet will be sent to that interface to be framed and sent out on the local network.
4. If the router is unable to locate an interface; the packets will be dropped.

Key Terms

Router – a router is a network layer device (layer 3 device) and provides the routing services within an internetwork.

Data packets – are used at the network layer to transport data through the internetwork.

Routed Protocols – are used to support data traffic.

Route Update Packets – are used to update neighboring routers about the networks connected to all routers within the internetwork.

Routing Protocols – are used to send out route updates packets.

Network Address

1. A protocol specific network address.
2. A router must maintain a routing table for individual routing protocols because each routing protocols keep track of a network with a different addressing scheme (ex. IP, IPv6, and IPX).

Interface – is the exit interface a packet will take when destined for a specific network.

Metric – is the distance to the remote network.

Visual of Windowing

 

Windowing Diagram

Window size of 1 = sending machine waits for an acknowledgement for each data segment it transmit before transmitting another segment.

Window size of 3 = allowed to transmit three data segments before an acknowledgement is actually received.

Types of flow control and a closer look at Windowing

 

The three types of flow control consists of:

1. buffering
2. windowing
3. congestion avoidance

A closer look at what windowing is and it's function at the transport layer

Windowing

• Windowing is the quantity of data segments (measured in bytes) that the transmitting machine is allowed to send without receiving an acknowledgement for them.
• In other words, it's the break of time in between data segments of before and after.
• Windowing is used to control the amount of outstanding, unacknowledged data segments.

Note: if hosts fails to receive all segments that it should have acknowledged, the host can improve the communication session by decreasing window size.

Connection-oriented Communication

Note: Recall that connection-oriented communications takes place in conjunction with flow control. These communication sessions, in combination of the protocols involved, provide for reliable data transports at the transport layer.

Diagram:

This is what we call the "Three Way Handshake"

1. The 1st "connection agreement" segment is a request for synchronization.
2. At the 2nd and 3rd connection agreement, segments acknowledge the requests and establishes connection parameters (the rules) between hosts. These segments request that the receiver sequencing is synchronized here as well, resulting in a bidirectional connection.
3. The final segment is also an acknowledgement. It notifies the destination host that the connection has been established – Data transfer can now begin.

How to identify a connection-oriented communication when you see one

1. It has a virtual circuit set up. (i.e.. 3 way handshake)
2. Use sequencing
3. Use acknowledgements
4. Use flow control

Question: What happens when a device receives a flooding of datagram's (packets) too quickly for it to process?

Answer: They store them in a memory section called a buffer.

Understanding how flow control operates at the Transport layer

A quick overview of the Transport layer and its function:

• Reliable networking is used at the transport layer
  • Reliable networking = using acknowledgements, sequencing, and flow control in the network.
• Segments and reassembles data into a data stream from the upper application layer and unites the information into the same data stream for further processing.

Flow Control

• Flow control prevents a sending host on one side of the connection from overflowing the buffers in the receiving host.
  • an event that can result in data loss
• Reliable data transports and employs a connection oriented communications sessions between systems and the protocols involved, to ensure that the following will be achieved:
  • Segments delivered are acknowledged back to the sender upon their reception.
  • Any segments not acknowledged are re-transmitted.
  • Segments are sequenced back into their proper order upon arrival at their destination.
  • A manageable data flow is maintained in order to:
    • avoid traffic congestion
    • overloading
    • data loss
• The purpose of flow control is to provide means for the receiver to be able to govern the out of data sent by the sender.

Important additional functions of the OSI reference model's upper layers

 

Application layer

• The application layer acts as an interface between the actual applications programs.
  • Example - Microsoft Word – actually does not reside at the application layer, but instead just interfaces at the application layer protocol, using data presented to it by the presentation layer.

Presentation layer

• The presentation layer presents data to the application layer up top.
• Responsible for data translation and code formatting.
• Acts as a translator that presents and provides coding and conversion functions.
  • Example – EBCDIC to ASCII
• Some presentation layer may also involves multimedia operations too.

Session Layer

• The session layer is responsible for setting up, managing, and then tearing down sessions between layer entities.
• Coordinates communication between systems and serves to organize their communication by offering THREE different modes:
  • Simplex
  • Half Duplex
  • Full Duplex
• Keeps different application data separate from other applications data.

A quick overview of the OSI layers and their functions

Applications

• file
• print
• message
• database
• application services

Presentations

• data encryption
• compression
• translation

Session

• dialog control

Transport

• end-to-end connection

Network

• routing

Data Link

• framing

Physical

• physical topology

Facts and notes on the OSI reference model bottom layers

The bottom layers of the OSI reference model include

1. Transport
2. Network
3. Data Link
4. Physical

Functions at each of the bottom layers

Transport
- provides reliable or unreliable delivery
- performs error correction before re-transmit

Network
- provides logical addressing, which routers use for path information

Data Link
- combines packets into bytes and bytes into frames
- provides access to media, using MAC address
- performs error detection, NOT correction

Physical
- moves bits between devices
- specifies voltage, wire speed, and pin-out of cables

The following operates at all seven layers of the OSI reference model

1. Network Management Stations (NMS)
2. Web and application servers
3. Gateways (not default gateways)
4. Network Hosts

Facts and notes on the OSI reference model

1. The OSI reference model has seven layers and is divided into two groups.
2. The top three layers define how the applications within the end stations will communicate with each other and with users.
3. The bottom four layers define how data is transmitted end to end.

The upper layers of the OSI reference model include

1. Application layer
2. Presentation layer
3. Session layer

*Note: Users interfaces with computer at the application layer.

*Note: The upper layers are responsible for applications communications between hosts.

Diagram

Advantages of using an OSI reference model

Advantages of using an OSI model include:

1. Prevents changes in one layer from affecting other layers.
2. Divides the network communication process into smaller and simpler components, thus aiding components development, design, and troubleshooting.
3. Allows multiple-vendor development through standardization of network components.
4. Encourages industry standardization by defining what functions occur at each layer of the model.
5. Allows various types of hardware and software to communicate

*Reference model: conceptual blueprint of how communications should take place.

*Binding: communication processes that are related to each other are bounded, or grouped together, at a particular layer.

Tips on network, routers, and switches

1. Plan your network design carefully.

2. Use network bridge in network to reduce collisions within broadcast domains and to increase the number of collision domains in your network.

3. Using hubs can contribute to traffic congestion.

4. Routers break up collision domains as well as broadcast domains.

5. Although bridges/switches are used to segment networks, they WILL NOT isolate broadcast or multicast domains.

6. Even though you have a switched network, you still need a router to provide your inter-VLAN communication or internetworking.

The OSI reference model and it's seven layers

The OSI reference model has seven layers:

Application layer (layer 7)
Presentation layer (layer 6)
Session layer (layer 5)
Transport layer (layer 4)
Network layer (layer 3)
Data Link layer (layer 2)
Physical layer (layer 1)