How to Find Network ID and Host ID

To find Network ID and Host ID

192.168.100.1/31
Default subnet = /24 there 24 bits 1 
                      = 11111111 11111111 11111111 00000000
                      = 255.255.255.0
There 31 bits 1 in subnet mask = 11111111 11111111 1111111 11111110
decimal = 255.255.255.254

To find Network ID = Count bit 1 in the octet that there is not in the default subnet octet
                                 111111111 11111111 11111111 11111110

                                 2^7 = 128 network

To find Host ID = Count bit 0
                             2^1 = 2  host