Subnetting...a bit confused on this.

Ok, I'm a little confused on this. This is taken out of the Sybex book 640-801. This is a practice question from the book. I get the concept of the problem, but can't seem to understand something. Here it goes:

We need to figure out the subnets, host, valid subnets, and broadcast address.

Network Address: 192.168.10.0
Subnet Mask: 255.255.255.240

SUBNET \BROADCAST ADDRESS

192.168.10.16 - 192.168.10.31 <---Subnet Zero??? Not Valid???
192.168.10.32 - 192.168.10.47
192.168.10.48 - 192.168.10.63
192.168.10.64 - 192.168.10.79
192.168.10.80 - 192.168.10.95
192.168.10.96 - 192.168.10.111
192.168.10.112 - 192.168.10.127
192.168.10.128 - 192.168.10.145
192.168.10.144 - 192.168.10.159
192.168.10.160 - 192.168.10.175
192.168.10.176 - 192.168.10.191
192.168.10.192 - 192.168.10.207
192.168.10.208 - 192.168.10.223
192.168.10.224 - 192.168.10.239 <---All 1's subnet??? Not Valid???

First host: Last host:

17

---

30
33

---

46
49

---

62
65

---

78
81

---

94
97

---

110
113

---

126
129

---

142
145

---

158
161

---

174
177

---

190
193

---

206
209

---

222
225

---

238

The question I have here is, if Cisco says the 1st subnet it's invald "illegal"
why would the first host be 17??? Shouldn't the first host be 33??? and isn't this subnet considered subenet-zero--->192.168.10.16 - 192.168.10.31

And is the all 1's subnet not valid either so why would the last host be 238. All ones subnet--->192.168.10.224 - 192.168.10.239 ???


FYI...This problem came from pgs. 110-111 on the Sybex Book 640-801.

Any help with this would be of great help !!!