Faster ways of Identifying the Network and Broadcast Address of a Subnet?

particle1

Hi,

I am about to take my N10-005 and and feel fairly confident.

To identify the Network and Broadcast Address of a Subnet I have been using binary arithmetic/boolean operators. I definitely have it down, however I want to know if this is how people actually do it in the real world, or do the use their 'formulas' to obtain the answers quicker.

I was reading in another sub forum that for higher level Cisco certs you need to be able to do the math alot quicker than the min or 2 it may take me. Is the way I am doing it acceptable?

Appreciate it!

Hondabuff

Take the subnet mask and identify the interesting octet. 255.255.255.248. 248 is our interesting octet. Take 256 -248=8, Now you know your block size of the subnet will be 8. Take 8-2=6. 6 is the amount of hosts you can have. This works with the 128,192,224,240,248,252,254 scale that you had to memorize. A subnet mask can only be 255.x.x.x where x=one of those masks. Network ID is the block size, add 1 is the first usable host, subtract 1 is the broadcast the of the subnet before. Blocks for 248 are 0-7, 8-15, 16-23 and so on. 192.168.1.58 255.255.255.248 count up by 8's, 8,16,24,32,40,48,56,64. 58 falls in-between 56 and 64. 56 is network ID and 63 is broadcast ID. Usable hosts are 57-62