said by contractor :
192 (7bits) splits the range in half = 128 addresses ...
64 (5 bits).
...
... or 2^4 (32-4 which is 2^4)
a /23 is 1000 and change.
Damn you people suck at math.
192 is not 7 bits... 192 = 1100.0000b, or
6 bits -- 64 addresses (one quarter)
64 is 2^6 or 6 bits. (again)
/23 is 2 class C's (2 /24's) and it's exactly 512 addresses.
a.b.c.d/x -> x is a "prefix length". It's the number of bits in the address that matter to routing (i.e. the "network") ranging from 0 to 32, where 0 is "no bits matter" (a default route) and 32 is "all bits matter" (a single host)
A prefix and netmask are different ways of writing the same thing. "/24" is 255.255.255.0 [8+8+8+0=24] The size of a network (in total addresses) is the number of bits that "don't matter" -- [0+0+0+8]. So for various prefixes...
•/24 - 255.255.255.000 [0000.0000b] - 2^[32-24=8] = 256
•/25 - 255.255.255.128 [1000.0000b] - 2^[32-25=7] = 128
•/26 - 255.255.255.192 [1100.0000b] - 2^[32-26=6] = 64
•/27 - 255.255.255.224 [1110.0000b] - 2^[32-27=5] = 32
•/28 - 255.255.255.240 [1111.0000b] - 2^[32-28=4] = 16
•/29 - 255.255.255.248 [1111.1000b] - 2^[32-29=3] = 8
•/30 - 255.255.255.252 [1111.1100b] - 2^[32-30=2] = 4