Supernetting advice

blatini

Hey guys. For the most part everything on ICND2 is coming to me very quickly. However I am having a hard time wrapping my head around supernetting, or I guess a quick way to solve questions involving it. I have a really easy time on subnettingquestions.com using the magic number theory, but it isn't carrying over as much as I'd like.

Does anyone have any tips in what to focus on? What resources were most useful to you in figuring it out?

boredgamelad

Do you have some specific examples you're having trouble solving?

blatini

Not off hand... I'm hoping there is a good rule of thumb someone has for it or a overall plan of attack that worked best? I suppose I should go find an example, but it's largely how to break the problems down to start.

theodoxa

Supernetting is just the opposite of subnetting. Instead of borrowing host bits to create smaller subnets, you "borrow" network bits to create a larger supernet. For example, you could take 8 Class C (/24) networks and combine them into 1 (/21) supernet. If you think of it in classless terms it makes sense. Just [temporarily] forget everything you learned about address classes.

192.168.0.0/21 (8 Class C networks combined into a supernet) for example would have a valid host range of 192.168.0.1 - 192.168.7.254 (2046 hosts).

blatini

And in that case you would have 5 subnet bits (32) ? So the octet that has been 'supernetted' will indicate the # of subnets every time?

JeanM

5 bits in 3rd octet yes, or 21 total giving you more bits for hosts... nnnnnnnn.nnnnnnnn.nnnnnhhh.hhhhhhhh