Chapter 11 — answers
Problem 1 — 10.20.0.0/24, largest first:
| Order | Department | Need | Prefix | Network | Usable | Broadcast |
|---|---|---|---|---|---|---|
| 1 | Wi-Fi guests | 100 | /25 | 10.20.0.0 | .1 – .126 | 10.20.0.127 |
| 2 | Sales | 60 | /26 | 10.20.0.128 | .129 – .190 | 10.20.0.191 |
| 3 | Engineering | 25 | /27 | 10.20.0.192 | .193 – .222 | 10.20.0.223 |
| 4 | Management | 10 | /28 | 10.20.0.224 | .225 – .238 | 10.20.0.239 |
| 5 | Link 1 | 2 | /30 | 10.20.0.240 | .241 – .242 | 10.20.0.243 |
| 6 | Link 2 | 2 | /30 | 10.20.0.244 | .245 – .246 | 10.20.0.247 |
Used: 248 of 256. Left over: 10.20.0.248 – .255.
Problem 2 — 172.16.0.0/22 (that's 172.16.0.0 – 172.16.3.255):
| Order | Area | Need | Prefix | Network | Usable |
|---|---|---|---|---|---|
| 1 | Floor 1 | 200 | /24 | 172.16.0.0 | 172.16.0.1 – 172.16.0.254 |
| 2 | Floor 2 | 200 | /24 | 172.16.1.0 | 172.16.1.1 – 172.16.1.254 |
| 3 | Floor 3 | 100 | /25 | 172.16.2.0 | 172.16.2.1 – 172.16.2.126 |
| 4 | Servers | 50 | /26 | 172.16.2.128 | 172.16.2.129 – 172.16.2.190 |
| 5 | Management | 20 | /27 | 172.16.2.192 | 172.16.2.193 – 172.16.2.222 |
Used: 736 of 1024. Left over: 172.16.2.224 – 172.16.3.255.
Problem 3 — the four /24s 192.168.4.0 through 192.168.7.0 combine into
192.168.4.0/22.
Why: in binary, the third octet values 4, 5, 6, 7 are 00000100, 00000101,
00000110, 00000111. The first six bits are identical (000001), so
16 + 6 = 22 bits are common → /22.