Network and broadcast addresses for classless subnets

[deanwebb]

What tips/tricks/memory devices do you use to remember network and broadcast addresses for /22, /23, /25, /26, /27, /28, /29, and /30 networks? Not just one or two, but all of them? Or do you just brute force it and memorize them by rote?

[Netwörkheäd]

Brute force memorization or calculation. Network is even, broadcast is odd.

[deanwebb]

I like to calculate. Once I have the number of hosts, including broadcast and network IPs, then I start counting at 0 and every multiple of that host number all the way up. The trick is remembering that the first (x) IP addresses of a range always start on the even number and end on an odd number.

In the case of a /28 network, every 16 is the START of a network and every 16x-1 is the END of a network... 0, 16, 32, 48, 64, 80, 96, 112, 128, and so forth for the network IPs and then one less for the broadcast.

And yay for numbers like 64, 128, and 192 for showing up often enough in these schemes so that they can serve as "mile markers" along the way.