How do you determine the subnet broadcast

Something like x.x.x.255

Well.. It won't always end with 255.. Infact in a subnet.. I really won't ever...


The broadcast is the last address int he subnet...

So if you had a subnet of:
192.4.54.0-192.4.54.15 with a mask of 255.255.255.240, 192.4.54.15 is the broadcast... And 192.4.54.1 is the network address...

255.255.255.255 /32 Host (single address)
255.255.255.254 /31 not usable
255.255.255.252 /30 4
255.255.255.248 /29 8
255.255.255.240 /28 16
255.255.255.224 /27 32
255.255.255.192 /26 64
255.255.255.128 /25 128
255.255.255.0 /24 256 ("Class C")
255.255.254.0 /23 512
255.255.252.0 /22 1024
255.255.248.0 /21 2048
255.255.240.0 /20 4096
255.255.224.0 /19 8192

Originally posted by The Prohacker

So if you had a subnet of:
192.4.54.0-192.4.54.15 with a mask of 255.255.255.240, 192.4.54.15 is the broadcast... And 192.4.54.1 is the network address...

You're slipping :), in the subnet you listed:

192.4.54.0-15 .15 would be the broadcast, but .0 would be the network address.

To answer the original question, you can determine the broadcast address of a netblock by knowing an IP Address and the netmask.

Again, using Prohacker's example, the netmask for 192.4.54.0-15 is 255.255.255.240 so if I want to know the broadcast address of 192.4.54.3 255.255.255.240 it is always going to be 192.4.54.15.

Eck!... Number one reason why not to do subnetting late at night :D

Originally posted by The Prohacker
Eck!... Number one reason why not to do subnetting late at night :D


:D -- even worse than doing subnetting late at night: Creating access lists :)

Originally posted by uuallan



:D -- even worse than doing subnetting late at night: Creating access lists :)


I have enough trouble with that during the day :D I don't even try at night :stickout