Subnetting Networks

Assignment Overview
Subnetting
A subnetwork, or subnet, is a logically visible subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting. All computers that belong to a subnet are addressed with a common, identical, most-significant bit-group in their IP address. This results in the logical division of an IP address into two fields, a network or routing prefix and the rest field or host identifier.
Why We Need Subnets
To understand why we need subnets (short for subnetwork), let’s start right from the beginning and recognize that we need to talk to "things" on networks. Users need to talk to printers, email programs need to talk to servers, and each of these "things" needs to have some sort of address. This is no different from a house address, but with one minor exception: the addresses need to be in numerical form. It is not possible to have a device on a network that has alphabetical characters in its address like "23rd Street." Its name can be alphanumeric - and we could translate that name to a numeric address - but the address itself must be numbers alone.
These numbers are called IP addresses, and they have the important function of figuring out not only the address of "things," but how communication can occur between them. It is not enough to just have an address. It is necessary to figure out how a message can be sent from one address to another.
This is where a little organization comes into play. 
It is often necessary to group things on a network together for both organizational and efficiency’s sake. For example, let’s say you have a group of printers in your company’s marketing department and a different bunch in the sales offices. You want to limit the printers that each user sees to those of each department. You could accomplish this by organizing the addresses of these printers into unique subnets. A subnet then, is a logical organization of connected network devices.
Each device on each subnet has an address that logically associates it with the others on the same subnet. This also prevents devices on one subnet from getting confused with hosts on the other subnet.
In terms of IP addressing and subnets, these devices are referred to as hosts. So, in our example, there is a network (the company), which is divided into logical subnets (marketing and sales departments), each of which has its own hosts (users and printers).
Understanding Subnetting
Subnetting allows you to create multiple logical networks that exist within a single Class A, B, or C network. If you do not subnet, you are only able to use one network from your Class A, B, or C network, which is unrealistic.
Each data link on a network must have a unique network ID, with every node on that link being a member of the same network. If you break a major network (Class A, B, or C) into smaller subnetworks, it allows you to create a network of interconnecting subnetworks. Each data link on this network would then have a unique network/subnetwork ID. Any device, or gateway, connecting n networks/subnetworks has n distinct IP addresses, one for each network / subnetwork that it interconnects.
In order to subnet a network, extend the natural mask using some of the bits from the host ID portion of the address to create a subnetwork ID. For example, given a Class C network of 204.17.5.0 which has a natural mask of 255.255.255.0, you can create subnets in this manner:
204.17.5.0 - 11001100.00010001.00000101.00000000
255.255.255.224 - 11111111.11111111.11111111.11100000
--------------------------|sub|----
By extending the mask to be 255.255.255.224, you have taken three bits (indicated by "sub") from the original host portion of the address and used them to make subnets. With these three bits, it is possible to create eight subnets. With the remaining five host ID bits, each subnet can have up to 32 host addresses, 30 of which can actually be assigned to a device since host ids of all zeros or all ones are not allowed (it is very important to remember this). So, with this in mind, these subnets have been created.
204.17.5.0 255.255.255.224 host address range 1 to 30
204.17.5.32 255.255.255.224 host address range 33 to 62
204.17.5.64 255.255.255.224 host address range 65 to 94
204.17.5.96 255.255.255.224 host address range 97 to 126
204.17.5.128 255.255.255.224 host address range 129 to 158
204.17.5.160 255.255.255.224 host address range 161 to 190
204.17.5.192 255.255.255.224 host address range 193 to 222
204.17.5.224 255.255.255.224 host address range 225 to 254
Note: There are two ways to denote these masks. First, since you are using three bits more than the "natural" Class C mask, you can denote these addresses as having a 3-bit subnet mask. Or, secondly, the mask of 255.255.255.224 can also be denoted as /27 as there are 27 bits that are set in the mask. This second method is used with CIDR. With this method, one of these networks can be described with the notation prefix/length. For example, 204.17.5.32/27 denotes the network 204.17.5.32 255.255.255.224. When appropriate the prefix/length notation is used to denote the mask throughout the rest of this document.
The network subnetting scheme in this section allows for eight subnets, and the network might appear as:
Figure 1. A subnetting scheme.
Notice that each of the routers in Figure 1 is attached to four subnetworks, one subnetwork is common to both routers. Also, each router has an IP address for each subnetwork to which it is attached. Each subnetwork could potentially support up to 30 host addresses.
This brings up an interesting point. The more host bits you use for a subnet mask, the more subnets you have available. However, the more subnets available, the less host addresses available per subnet. For example, a Class C network of 204.17.5.0 and a mask of 255.255.255.224 (/27) allows you to have eight subnets, each with 32 host addresses (30 of which could be assigned to devices). If you use a mask of 255.255.255.240 (/28), the break down is:
204.17.5.0 - 11001100.00010001.00000101.00000000
255.255.255.240 - 11111111.11111111.11111111.11110000
--------------------------|sub |---
Since you now have four bits to make subnets with, you only have four bits left for host addresses. So in this case you can have up to 16 subnets, each of which can have up to 16 host addresses (14 of which can be assigned to devices).
Take a look at how a Class B network might be subnetted. If you have network 172.16.0.0 ,then you know that its natural mask is 255.255.0.0 or 172.16.0.0/16. Extending the mask to anything beyond 255.255.0.0 means you are subnetting. You can quickly see that you have the ability to create a lot more subnets than with the Class C network. If you use a mask of 255.255.248.0 (/21), how many subnets and hosts per subnet does this allow for?
172.16.0.0 - 10101100.00010000.00000000.00000000
255.255.248.0 - 11111111.11111111.11111000.00000000
-----------------| sub |-----------
You are using five bits from the original host bits for subnets. This allows you to have 32 subnets (25). After using the five bits for subnetting, you are left with 11 bits for host addresses. This allows each subnet so have 2048 host addresses (211), 2046 of which could be assigned to devices.
Note: In the past, there were limitations to the use of a subnet 0 (all subnet bits are set to zero) and all ones subnet (all subnet bits set to one). Some devices would not allow the use of these subnets. Cisco Systems devices allow the use of these subnets when theip subnet zero command is configured.
To learn more about bipartite graphs and graph representations, check the following sites:
Introduction to Subnetting - A Must Known for Networking Professionals (www(dot)youtube(dot)com/watch?v=nhMtVsSXRng)
IP Subnetting Introduction (www(dot)youtube(dot)com/watch?v=61RKzsZo13c)
Subnetting introduction (www(dot)youtube(dot)com/watch?v=-U6ZHZdPgWU)
Learn to Subnet the Easy Way (www(dot)youtube(dot)com/watch?v=C4n2Ofqr6QY)
Subnetwork (http://en(dot)wikipedia(dot)org/wiki/Subnetwork)
8 Steps to Understanding IP Subnetting (http://www(dot)techopedia(dot)com/6/28587/internet/8-steps-to-understanding-ip-subnetting)
Introduction to subnetting (https://learningnetwork(dot)cisco(dot)com/servlet/JiveServlet/previewBody/10899-102-1-40597/Introduction%20to%20Subnetting.pdf)
Case Assignment
You are required to review the case materials and conduct your own research (at least three additional sources of materials. Please be sure to use appropriate citations for materials that you collect on your own), in your own words, please write a 2- to 3-page paper (excluding the cover page and reference page) to why subnetting is necessary and what happens if we do not subnet a network.
Assignment Expectations
Your paper should be between two and three pages. You are expected to understand the basic concept of static routing.
Upload your assignment when you are finished.