Is this right (subnetting)

jrmeulemans

The following are notes I wrote down on sub-netting. Can someone take a look and let me know if I'm wrong in any points. Oh and what is the point of the "AND" math...it seems that I don't need to use it in my example...is it only for checking your work?



1. Look at Class (A,B,C )
2. Look at Mask (How many bits used in Host portion?)
3. Take “left-over” bits to determine range of hosts (minus zero and broadcast )

Example:
IP Address: 200.1.1.8
This is a class C network
Subnet Mask: 255.255.255.248 (aka 200.1.1.8 /29)
Network is using 5/8 of the host portion (remember, class C: N.N.N.H)
248 = 128+64+32+16+8 (5 out of the 8 bits, counted left to right)
Leftover bits is 3 (4+2+1) = range of seven including zero
200.1.1.8 “zero” host**
200.1.1.9
200.1.1.10
200.1.1.11
200.1.1.12
200.1.1.13
200.1.1.14
200.1.1.15 broadcast address**
**Zero Address is simply when all the values to the right of the mask are 0’s, while the broadcast is when all the values to the right are 1’s. **

dynamik

Looks right. You use the AND operation when you have an IP address and a subnet mask, and you need to figure out which subnet that IP address belongs to. It's pretty obvious once you figure out the ranges, but that's how it works behind-the-scenes.

shednik

Yea that looks right for that network 200.1.1.8/29...one thing i always do like you did is find out the place where the last borrowed bit is. ie that last bit used in there is 8 so that will make the block size set to 8. So each subnet will interval by 8s, that just how I quickly can determine the network ranges in my head.

captobvious

Looks good to me.

I'd look at http://www.techexams.net/forums/ccna-ccent/38772-subnetting-made-easy.html

Helped me to pick it up quickly!

bubble2005

corretomundo

kevin31

Hi jrmeulemans

Just wondering what tools youo used to learn the technique? Ive been trying different methods still cant grasp it!

Thanks

Kev

mattrgee

In my opinion you cna't beat the Subnetting chapter in Todd Lammel's CCNA guide.

jrmeulemans

kevin31:

Cisco has a free e-learning section on their site that covers it:

http://www.cisco.com/E-Learning/bulk/subscribed/tac/cim/iprouting/basic_ip_routing_concepts/mod_frameset.htm


edit: oh yeah dude, you can also youtube a few decent vids on it....try and find one with an Australian guy with a whiteboard...