Should you ever forget intricacies of the subnetting Checkpoint bothered not to strip subnetting calculator from their Splat – ipcalc, so use it and litter not your memory with useless info.
Given subnet show the 1st Ip (network) :
# ipcalc -n 192.168.34.45/27
NETWORK=192.168.34.32
Given subnet show the last IP (broadcast) :
# ipcalc -b 192.168.34.45/27
BROADCAST=192.168.34.63
Be careful though what you feed as no proof-reading is done by the ipcalc :
# ipcalc -b 192.168.34.45/33
BROADCAST=255.255.255.255
The Subnet calculator start of with mask /25. If you are using 25 bits, your subnet mask is (check the lower part of the tool) 255.255.255.128, you can divide a old Class C network into two parts. Now slide the network address slider past 127, you will see that the Network Address changed from 192.168.0.0 to 192.168.0.128. You can also see that the broadcast address changed. If you want to make a list of all possible CIDR networks from the chosen mask/address press the Generate subnet list.