1. Training Guide Part 1 - Adding New VLSM Subnets
CIT/249

2. OVERVIEW Description of an IPv4 based WAN
How to calculate a subnet ID and subnet broadcast address
How to test for overlap in a VLSM scheme and troubleshoot issues that may arise from the overlap
Step-by-step illustration of how to add a new subnet

3. A overall description of an IPv4 based WAN
IPv4 is the 4th version of a Internet Protocol, its used to identify devices that the network has through a addressing system. The IP is setup for the use in a Interconnected system of packet switched computer communication networks.
IPv4 uses 32-bit addresses for network communication in five classes A-E. Class ABC have different bit length for addressing the network host. Class D is reserved for multicasting and Class E is saved for future use but originally saved for experiments.

4. A overall description of an IPv4 based WAN cont
The IP address identifies a system location on the Network. IP address must be unique to the internetwork and have a uniform format.
Each IP address includes a network ID and a host ID
The network ID identifies the system that are located on the physical network IP routers.
The Host ID identifies a workstation, servers, routers or other TCP/IP host within the network.

5. How to calculate a subnet ID and subnet broadcast address
Classful network total bits is 8. Sub-net mask can be 0, 128, 192, 224, 240, 248, 252, 254 and 255.
Subnet mask 255 is default, so it'll not consider for subnet masking
From the previous step, you got the "Number of bits used for subnetting"(n) and you know the "Tb", then you can get "Number of bits left for host"(m) = Tb - n as total bits is the summation of number of bits used for subnetting and number bits left for host i.e. Tb = m+n.
Number of bits left for host = m = Tb - n = = 5

6. How to calculate a subnet ID and subnet broadcast address cont
Now you have to calculate "Number of subnets" = 2n and "Value of last bit used for subnet masking"(Δ) = 2m. Number of host per subnet = 2m - 2.Number of subnets = 2n = 23 = 8 Value of last bit used for subnet masking = Δ = 2m = 25 = 32
.Now you can find previously calculated number of subnets by separating subnets each having "Value of last bit used for subnet masking" or Δ addresses.The 8 subnets (Each of them has 32 addresses.
Now you have to find that your IP address is in which subnet, that subnet's first address is network address and last address is broadcast address.

7. A clear explanation of how to test for overlap in a VLSM scheme and troubleshoot issues that may arise from the overlap
VLSM Overlapping considers the situation in which some ip addresses that are in a subnet, are also in another subnet, so the subnets overlaps and it should be avoided
Calculate the subnet ID and subnet broadcast address of each subnet, which gives you the range of addresses in that subnet.
Scan the list from top to bottom, comparing each pair of adjacent entries, to see whether their range of addresses overlaps.
need to analyze each subnet, finding not only the subnet ID but also the subnet broadcast address and the range of addresses in the subnet.
When you have a problem that give you some subnets (or ip addresses from which calculate subnets) and ask you to find which ones overlaps, you have to: order the subnets from the lowest to the highest; find the respective subnets broadcast address; compare if the usable ip addresses of a subnet are also in another subnet (overlaps)

8. A clear explanation of how to test for overlap in a VLSM scheme and troubleshoot issues that may arise from the overlap
Scan the list from top to bottom, comparing each pair of adjacent entries, to see whether their range of addresses overlaps.
need to analyze each subnet, finding not only the subnet ID but also the subnet broadcast address and the range of addresses in the subnet.
When you have a problem that give you some subnets (or ip addresses from which calculate subnets) and ask you to find which ones overlaps, you have to: order the subnets from the lowest to the highest; find the respective subnets broadcast address; compare if the usable ip addresses of a subnet are also in another subnet (overlaps)

9. step-by-step illustration of how to add a new subnet
Pick the subnet mask (prefix length) for the new subnet, based on the design requirements
Calculate all possible subnet numbers of the classful network using the mask from Step 1, along with the subnet broadcast addresses.
Make a list of existing subnet IDs and matching subnet broadcast addresses.
Compare the existing subnets to the candidate new subnets to rule out overlapping new subnets.
Choose the new subnet ID from the remaining subnets identified at Step 4, paying attention to whether the question asks for the numerically lowest or numerically highest subnet ID.

10. step-by-step illustration of how to add a new subnet
Make a list of existing subnet IDs and matching subnet broadcast addresses.
Compare the existing subnets to the candidate new subnets to rule out overlapping new subnets.
Choose the new subnet ID from the remaining subnets identified at Step 4, paying attention to whether the question asks for the numerically lowest or numerically highest subnet ID.

11. REFERENCES
Odom, W. (2016). Cisco CCENT/CCNA ICND official Cert guide.
protocol-version-4-ipv4