Show Quoted Text
If you keep 172.17.32.0/20 as is, you have just one big network (of course).
If you use a /28 mask, then you have the following subnets (relative to the original address and mask):
172.17.32.0/28 .00100000.0000 0000 (last two octets, space at /28)
172.17.32.16/28 .00100000.0001 0000
172.17.32.32/28 .00100000.0010 0000
172.17.32.48/28 .00100000.0011 0000 ...
172.17.32.240/28 .00100000.1111 0000 (16 subnets so far)
then:
172.17.33.0/28 .00100001.0000 0000 ...
172.17.33.240/28 .00100001.1111 0000 (other 16 subnets )
and so on until
172.17.47.0/28 .00101111.0000 0000 ...
172.17.47.240/28 .00101111.1111 0000
So, you have 16*16 subnets (eg, 256) if you use a /28 mask.
You can also see this very quickly if you think that you gain 8 bits for the subnet part (/20 -> /28), thus you have 2^8 = 256 subnets.
Ok, strictly speaking, you "gain" 255 subnets (you had one, and now you have
256), but I hope you got the idea.