Analyzing IP Networks – Answers, Exercise 2
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 | 9.9.9.9 | A | 9.0.0.0 | 9.255.255.255 |
| 2 | 99.99.99.99 | A | 99.0.0.0 | 99.255.255.255 |
| 3 | 199.199.199.199 | C | 199.199.199.0 | 199.199.199.255 |
| 4 | 119.119.119.119 | A | 119.0.0.0 | 119.255.255.255 |
| 5 | 229.229.229.229 | D | 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 | 9.0.0.0 | 9.0.0.1 | 9.255.255.254 | 9.255.255.255 |
| 2 | 99.0.0.0 | 99.0.0.1 | 99.255.255.254 | 99.255.255.255 |
| 3 | 199.199.199.0 | 199.199.199.1 | 199.199.199.254 | 199.199.199.255 |
| 4 | 119.0.0.0 | 119.0.0.1 | 119.255.255.254 | 119.255.255.255 |
| 5 | N/A | N/A | N/A | N/A |
Good thanks
Better 2nd exercise!
Thanks Len!
Hello,
I hope all is well.
May I ask why is 229.229.229.229 N/A? The address falls between 0-255.
Thank you
Hi Jared,
Thanks! Hope it’s going well with you, too.
The first octet, 229, tells us that the address comes from the class D range of addresses, reserved for multicast purposes. As a result, the class A, B, C rules to find the network ID, etc, do not apply. Those rules only apply in the unicast address range, from first octet 1-126 (class A), 128-191 (class B), and 192-223 (class C).
Wendell