Classful vs Classless

shanparames

Hi

Please explain which criteria differentiate a classful addressing from classless ip addressing!


151.78.1.1/25 ip address is a classless ip address or classful ip address?


I found an interesting discussion in this forum from: http://www.techexams.net/forums/ccna...m-vs-cidr.html

In this discussion, I found the statement as follows:

This is incorrect, i can have a classful routing protocol with an address
151.78.1.1/25, in this case i must use /25 throughout my network when using a 151.78.x.x network address.


So I need which factor either the first few bits of an ip address or the subnet mask decides it's type classful or classless?

Thanks

Swaminathan

Forsaken_GA

phoeneous wrote: »

For the purpose of the CCNA, classful addressing uses Class A, B, or C subnet masks and classless doesnt. So with classful addressing, you will have networks like 10.0.0.0/8, 172.16.0.0/16, and 192.168.1.0/24.

Sorry, don't mean to nitpick, but....... Classful networks may be notated as such, but for the most part, things are classful because they don't contain the subnet mask in their updates, the subnet mask is assumed based on what bits are flipped on in the first octet. Using CIDR notation when discussing classful networks can be a little misleading.

Long story short, classful networks have either predetermined network prefixes, or make assumptions based on the interface configuration.

Classless does away entirely with the concept of classful networking. Rather than using the bits in the first octet to automatically assume a subnet mask, the amount of bits used to mask that prefix are sent with the prefix as a requirement.

What it basically boils down to is that, in classful networking, the prefix is inferred by the router. In classless networking, the prefix is explicitly defined by the router sending the update.