Analyzing IP Networks – Answers, Exercise 1
Today’s post lists the answers to the previous post’s question, with a few comments, with a place to discuss. Nothing snazzy, but it does hit the fundamentals. Enjoy!
Related links:
- The original list of problems
- Post about how to find the answers
- Deeper info from the ICND1 OCG book
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 | 100.100.100.100 | A | 100.0.0.0 | 100.255.255.255 |
| 2 | 200.200.200.200 | C | 200.200.200.0 | 200.200.200.255 |
| 3 | 300.300.300.300 | None | N/A | N/A |
| 4 | 128.128.128.128 | B | 128.128.0.0 | 128.128.255.255 |
| 5 | 191.191.191.191 | B | 191.191.0.0 | 191.191.255.255 |
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 | 100.0.0.0 | 100.0.0.1 | 100.255.255.254 | 100.255.255.255 |
| 2 | 200.200.200.0 | 200.200.200.1 | 200.200.200.254 | 200.200.200.255 |
| 3 | N/A | N/A | N/A | N/A |
| 4 | 128.128.0.0 | 128.128.0.1 | 128.128.255.254 | 128.128.255.255 |
| 5 | 191.191.0.0 | 191.191.0.1 | 191.191.255.254 | 191.191.255.255 |
good first exercise!
Cool practice exercise to start working on IP networks daily!