Supernetting??

sleemie

I'm confused about what supernetting is...I've seen it both ways...

First, I've read that it's when you take for example a class A IP address and apply a class B type mask to create more networks than what normally would be available for a class A..for example..

120.30.0.0 and applying a mask of 255.255.224.0 to give yourself more networks.

then, i've read where it's the other way around, where you take like a class c and create more hosts than normally available, for example.

199.200.0.0 and applying like the same mask 255.224.0.0 to give yourself more hosts than a class C would normally have.

So, which one is supernetting?

Isn't CIDR simply the same thing? where you apply whatever mask you need to whatever IP address you need without regard to the class?

As I was trying to come up with an example, something else just dawned on me that I'm confused about...does the portion of an IP address that you're masking to create more subnets with have to be 0. like my C class address of 199.200.0.0, with a mask of 255.224.0.0...can you put a 224 mask on top of the 200? doesn't seem right to me, but not sure...would it have to be a class C of like 199.0.0.0 or 200.0.0.0 in order to do a mask like 255.224.0.0 or 255.192.0.0??

So, if the internic, or whomever manages that now, assigns a company a class C address of 199.254.201.0...does that mean they're limited to class C masks and you're not able to give yourself more than than 254 host addresses with supernetting or CIDR...such as 255.255.224.0.

and lastly, can we expect supernetting type questions on the exam? will I have to figure beyond the classful 126 max subnets?

SV

"Classless Inter-Domain Routing is an IP addressing scheme that replaces the older system based on classes A, B, and C. With CIDR, a single IP address can be used to designate many unique IP addresses. A CIDR IP address looks like a normal IP address except that it ends with a slash followed by a number, called the IP network prefix. For example:
172.200.0.0/16 " - http://www.webopedia.com/TERM/C/CIDR.html


Supernetting is similar to CIDR in certain way.

Supernetting combining several IP network addresses into one IP address. Supernetting reduces the number of entries in a routing table and is done in CIDR addressing as well as internal networks. - http://www.pcmag.com/encyclopedia_term/0,2542,t=supernetting&i=52240,00.asp

The above link will also give you an example.
The main purpose of doing supernetting is to reduce the number of entries we might have to write in a routing table.

This is how I understand it :-
Lets take an example of a group of people (sam, mike, steven, sandy, and jack). If I want sam, steven and sandy to stand up, I can either call each one of them and request them to stand, or I can tell the same in one shot asking every one starting with "s" to stand.

Now if I want only sam and sandy to raise their hand, we can just ask every one whose name starts with "sa" to do it.

Similarly the purpose is to group IPs to reduce number of entries to be made in certain situations.

As far as I know for CCNA you do not have to know in dept of supernetting. But should know what it is and why its done.

Note: Please correct me if I am wrong about the explanation.

sleemie

Thanx for the info...the web o pedia link you referred me to said it's the same as supernetting...