VLSM Block Size Table - Prefix sized incorrect?

[mid4]

Hi,

On Page 179 7 Edt. The table 5.1 should the prefix.

But I find that a 240 Mask has a prefix of /20 not /28. Could someone please explain how this works?

Thanks

Table attached in picture.

[bs_kwaj]

11111111 . 11111111 . 11111111 . 00000000 = 24 bits on - /24
11111111 . 11111111 . 11111111 . 10000000 = 25 bits on - /25
11111111 . 11111111 . 11111111 . 11000000 = 26 bits on - /26
11111111 . 11111111 . 11111111 . 11100000 = 27 bits on - /27
11111111 . 11111111 . 11111111 . 11110000 = 28 bits on - /28

And, you know, each of the octet's 8 positions have values:

128 64 32 16 8 4 2 1

/28 = .11110000 = 128 + 64 + 32 + 16 = 240

[mid4]

Thanks.

The table above (picture) says it is only for a class C address. Would you only use VLSM on a class C network?

Also I can't seem to understand why on pg 188 the ip address 192.168.144.0/20 is a subnet of 255.255.240.0. When the table above shows a 240 as a /28? (Question is on route summarization)

Thanks