TCP/IP and Subnet Masking


  • Level: Intermediate
  • Presenter: Eli the Computer Guy
  • Date Created: November 19, 2010
  • Length of Class: 69 Minutes



Purpose of Class

  • This class teaches students about the components and concepts in a TCP/IP network.


  1. TCP/IP Overview (2:32)
  2. How TCP/IP Works (16:53)
  3. TCP/IP Numbering (43:00)
  4. Subnet Masking (48:17)
  5. Final Thoughts (64:03)

Class Notes

  1. 1. TCP/IP
    1. Is technically a Protcol Suite
    2. IP Routes Traffic
      1. Layer 3 OSI Model Network
      2. Routable Networks (sub networks)
    3. TCP controls transmission between connected systems
      1. Layer 4 OSI Model  Transport
      2. Windowing is the process of sending data from one computer to another in TCP/IP version 4
  2. 2. How TCP/IP Works
    1. IP Addresses – Every device on a TCP/IP network needs an individual IP Address
    2. DNS (Domain Name Service/Server) resolves Domain names into IP Addreses
    3. DHCP (Dynamic Host Control Protcol) Servers automatically assign IP information to clients for a specific time period (Lease).  Clients try to renew leases at 50% expiration point.
    4. Default Gateway (Router) connects networks.  If an IP Address cannot be found on the local network the computer tries to use the Default Gateway to find the target.
    5. Subnets and Subnet Masking – Subnets are individual networks.  Subnet Masks divide IP Addresses in Subnet Number and Host Number
  3. What the Number Mean
    1. IP Addresses and Subnet Masks are made of 4 Octets of Bits
    2. 128-64-32-16-8-4-2-1
  4. Subnet Masking
    1. IP Addresses contain the Subnet Number and Host Number.  The Subnet Mask tells you where the subnet number ends and the host number begins.
    2. Classful Networks A, B, C,D,E  Gone now use CIDR
    3. The Highest Address in a Subnet Range is the Broadcast address
    4. To determine the number of subnets (n is the number of bits used)= 2n
    5. To determine number of Hosts = 2n -2


Eli the Computer Guy (2030 Posts)

Eli the Computer Guy has 16 years experience in technology being the guy to fix "it". From the Army, to building out new satellite offices for the enterprise, to running his own shop with 9 full time employees Eli has real world experience with almost all systems that technicians will be working with. Eli has 1600 hours of formal technical beyond his Bachelors Degree in Criminal Justice on technologies ranging from Avaya PBX/ Audix to Microsoft, Red Hat Linux, MySQL, Cisco and much more.

33 Responses to TCP/IP and Subnet Masking

  • Guens says:

    Great Job Mr Eli, thank you very much. Your video help me a lot.

  • Cédric says:

    Thank you it was great !
    Could you tell me please…
    Why do you and English speaking people use Bytes and Octets for the same thing ?
    It does get everyone confused !

  • Eli the Computer Guy says:

    There are 8 Bits in an Octet for subnet masking.

  • Cédric says:

    I think you didn’t get me, I know there are 8 bIts in a Octet but there are also 8 bIts in a BYte.
    Thus they are the exact same thing!!
    So question was why do you use BYte or Octet? Does it depends on the context ?
    And also, why is there a smile on the bottom left hand corner of your web pages??

  • Eli the Computer Guy says:

    It’s based on context. In IP Addresses we are worried about the bits, and those bits are grouped in 4 groups of eight. So although 8 bits do equal a byte, in subnet masking we are not concerned with bytes.

  • Jawad says:

    Awesome, great Job really nice work, really nice method for converting Decimal into binary numbers….. that helped me alot. gone through all of your lectures all are very great & detailed. Thanks Alot Man. May God bless you.

  • Jason Martin says:

    Thanks Eli, your awesome!

  • Vincent Pious says:

    I Eli,
    I happened to download one of your tutorials on TCP/IT which I find so useful for my Network+ lesson which I’ve just begun. As a network+ student, I would really love to have access to IT materials that will easily help me to understand concepts which are difficult to absorb.

    I would be very grateful if u would help me with more learning material especially on how to determine which hosts are on the same network and those that are not.
    Thank u.

  • Amal says:

    Thank alot for this video its very helpful, but I have a question if can answer it.
    If we have an ip address and have two network which are, A and B. In A it has 25 hosts and B it has 7 hosts. and this network hosts will doubled after two years. What will be the subnetting for A and B, by find the following:

    *Number of bits in the subnet:
    *IP mask (binary)
    *New IP mask (decimal):
    *Maximum number of usable subnets (including the 0th subnet)
    *Number of usable hosts per subnet:
    *IP Subnet:
    *First IP Host address:
    *Last IP Host address:

    I hope to help me and I will be very thankful for you.


  • mark says:

    Thank you very much for these classes :)

    I’m a little confused though, when you explained how NAT works in routers, does NAT exist in modems too? and also can modems be configured like routers like when you want to configure a router you enter the IP of the router in browser or via telnet etc. and you can configure it. Can that be done with modems as well?


  • Jarod says:

    Aren’t DHCP reservations preferred addresses, but not static? I know how to give a computer a static address, but how do give devices with no interface a static IP address. A Fax server is just a box, Voicemail server, or a Phone software server.

  • Eli the Computer Guy says:

    If you don’t have an interface then you can’t have an IP address at all. The IP is configured for the network card on the computer or device.

  • Jarod says:

    I’m unaware of the correct procedure, I hear different solutions. I hear give the devices DHCP reservations and then make the devices themselves static through TCP/IP. Then I hear don’t use an address within the scope of the DHCP at all for servers. How do I give an unattached device a specific IP address outside the scope of the DHCP? Also, do I create an OU in the active directory and add these devices? I’m new to all of this. Lastly, does your company offer retainer services?

  • Eli the Computer Guy says:

    OU’s are not part of this.

    The easiest way to do it is to create a DHCP Scope of 100-225, and then give all the devices static IP addresses below 100.. So I will create the 100-225 scope and then for managements sake I will give networking devices IP addresses between 2-10, servers IP between 11-20, printers and such between 21-30, etc.

    Static IP addresses are set on the device/ computer itself. You sit down at the computer and give it the static ip address through it’s configuration panel.

  • Yuk Murany says:

    I have to say that for the last couple of hours i have been hooked by the impressive articles on this website. Keep up the good work.

  • Sagar says:

    Eli i have been searching for the exact and clear definition of “PORT”. Could you please explain what it is?

  • Nathemnael says:

    Thanks very much u give me a lot of knowledge.

  • Alexandru says:

    Very good presentation, many people knows networking but few knows how to explain so everybody understands. I was wondering if you don’t have any videos regarding packet tracer application tutorials , that would be very useful.
    Regards, Alexander

  • Mohamed Mubeen says:

    Hai Eli i am from India
    thanks for posting your classes
    it helps me very much
    i am studying hardware classes with my friends we are having only low level knowledge in hardware and networking
    but your classes gives me a great knowledge about computer
    now i have great knowledge about computer with your tutorials comparing with my friends

    once again thanks
    and your are my roll model also

  • Assaf says:

    Dear Eli,

    On behalf of all our viewers and the staff,
    I would like to thank you personally from the bottom of my heart
    for your technological generosity.

    You are what is all about,
    Each One, Reach One Teach One.

    Assaf Ben-Haim

  • Hi Eli,
    Thank you very much for these free videos. I am taking CompTIA Network+ and Cisco CCNA1.
    Network Mapping and TCP/IP and Subnet Masking the volume is very low, please fix it.
    Thank you,

  • Aliyu from Lagos Nigeria says:

    Hi Eli, Im enjoying your videos but my problem is Im new in IT,I dont know how to download the videos.Pls help

  • Sheikh wasiu AL hasib says:

    Thank you very much for this type of free training. I like your training very much because it is very easy to understand. I want training about CCNA. If u have this training video please include this in this website.
    I will be very pleased .

  • Adriano Vasco says:

    Hi Eli!

    How to install and configure DNS in Linux?

  • Mario says:

    Hello Eli !

    Excellent Job man!!! You are a great teacher!

    I have two questions about Windowing. I hope you can answer. What would happen if for example the sender does not receive an acknowledgment? And the other one is, if for example some errors ocurred during transmission, the window size it will be the same at the beginning? or it could be smaller ?


  • Sallah Joseph says:

    your job is really suberb; your website has attracted all my attentions. Thanks once more my lecturer

  • Juris says:

    Hi! Thanks for great tutorials!!!
    Just wondering – what happens if DNS server is down?
    What won’t work?

  • Amit Tiwari says:

    you are simply awsome !! You cleared lot of topics to me….thanks !

  • Levi says:

    your are the best, tomorrow i have a network test and now i have understand the subnet mask etc….

  • Alex Deva says:

    Hy , i think there is a problem with the sound in this movie , announce me when is done , thanks Eli :D

  • charles says:

    very good toturial

  • baisemain says:

    I can’t hear anything. This is very unfortunate. How can I fix this?

  • Mark says:

    Thank you for such an informative lesson/class..honestly I feel like I collected a few “packets” out of the millions on offer, but hopefully watching this again..and maybe again..they will start to transmit into something more mentally substantial! :)

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