Analyzing IP Networks #3
This is the My Dear Aunt Sally (Multiplcation/Division/Addition/Subtraction) of the IP addressing and subnetting world. Nothing snazzy, just some exercises and a place to ask questions.
For each Analyzing IP Networks post, you have several simple analysis tasks related to classful networks (that is, class A, B, and C networks.) Work on making this analysis automatic and second nature!
Videos: How to and More Practice
The video on the left teaches you how to analyze classful networks to determine the network class of the address, plus four key facts about the related class A, B, or C network. The other two videos give you more practice problems beyond this practice problem post.
The Problems
Each problem starts with a Dotted Decimal Notation (DDN) number. Your job:
- Determine the class (A, B, C, D, E, or none)
- If A, B, or C:
-
- Find the Network ID
- Find the Network Broadcast Address
- Find the numerically lowest and highest IP addresses that can be used by hosts in the network
Table 1 lists the five problems.
Table 1: Five Problems for Today’s Post
| DDN Value | Class | |
| 1 | 126.0.0.1 | |
| 2 | 192.0.0.1 | |
| 3 | 223.0.0.1 | |
| 4 | 1.1.1.1 | |
| 5 | 123.321.123.321 |
Answers Below: Spoiler Alert
Class, Network ID, and Network Broadcast
The Network ID can be derived from the class A, B, or C DDN value by copying the network octets, and writing a 0 for the rest of the octets. Similarly, the network broadcast address can be found by using the same logic, but writing a 255 instead of 0 for the host octets. Table 2 shows the class for each of the five problems, along with the derived network ID and network broadcast address for each class A, B, or C address.
Table 2: Network IDs and Network Broadcast Addresses
| DDN Value | Class | Network ID | Network Broadcast Address | |
| 1 | 126.0.0.1 | A | 126.0.0.0 | 126.255.255.255 |
| 2 | 192.0.0.1 | C | 192.0.0.0 | 192.0.0.255 |
| 3 | 223.0.0.1 | C | 223.0.0.0 | 223.0.0.255 |
| 4 | 1.1.1.1 | A | 1.0.0.0 | 1.255.255.255 |
| 5 | 123.321.123.321 | N/A | N/A | N/A |
Usable Host IP Addresses
To find the range of IP addresses that can be used by hosts in the (unsubnetted) classful network, just add 1 to the network ID and subtract 1 from the network broadcast address. Table 3 shows the results for these five problems.
Table 3: Ranges of Usable Addresses
| Network ID | Lowest Usable Host Address | Highest Usable Host Address | Network Broadcast Address | |
| 1 | 126.0.0.0 | 126.0.0.1 | 126.255.255.254 | 126.255.255.255 |
| 2 | 192.0.0.0 | 192.0.0.1 | 192.0.0.254 | 192.0.0.255 |
| 3 | 223.0.0.0 | 223.0.0.1 | 223.0.0.254 | 223.0.0.255 |
| 4 | 1.0.0.0 | 1.0.0.1 | 1.255.255.254 | 1.255.255.255 |
| 5 | N/A | N/A | N/A | N/A |
This problem requires that you determine the IPv4 address class of a DDN number. To do that, you can compare the first octet value to the values in the following table.
| First Octet Range | Class |
|---|---|
| 1-126 | A |
| 128-191 | B |
| 192-223 | C |
| 224-239 | D |
| 240-255 | E |
Shouldn’t the 5th question be CLASS A?
Network: 123.0.0.0
Broadcast: 123.255.255.255
First: 123.0.0.1
Last: 123.255.255.254
nvm, just noticed the 321
Technically no since the address is invalid. The DDN value 123.321.123.321 has numbers in the second and fourth octets that are above 255 which is the max value in an octet.