Differences between Classful & Classless Subnetting?

ameen.ahmed · ‎05-24-2011

Friends,

What are the differences between classful and classless subnetting?

It's confusing, please help.

Thanks,

Ameen Ahmed.

mcusine · ‎05-24-2011

Hi Ameed,

The diference between the classfull routing and classless routing are the next.

Classful routing Protocol : does't send subnet mask info at what time a route update is send out. Each and every one device in the system has to make use of the similar subnet mask. Classfull routing does not allows Variable Length Subnet Masking. You have always the complete mask of the classess 255.0.0.0 255.255.0.0 or 255.255.255.0 example for rouitng protocol that only allow calssfull mask it's Rip V1

Classless routing sends subnet mask info within the routing updates. Classless routing allows Variable Length Subnet Masking. Yo can make subnetting with classless. Routing protocolos that support it RIP V2 EIGRP & OSPF.

Hope thise help.

Regards,

Mauricio

Joseph W. Doherty · ‎05-25-2011

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Classful subnetting is using part of a classful IP address host address as a network address. For example, if I take a class C address, which the network address part of the IP address is the first 24 bits, and use the next 6 bits also as part of the network address, the group of networks created are subnets of the class C address.

If I take a class B address, and use the next 8 bits, the created network addresses are subnets of the class B. In this later case, the network mask would be the same as for a class C address, but a natural class C is not a subnet of a class B or class A address.

The difference, in classful addressing, between natural classful addresses and subnetted classful addresses comes into play when working with classful routing protocols; where there are many dos and don'ts.

One might argue, there isn't any subnetting of classless addresses since each network address is defined with the number of leading bits that comprise the network part of the address, i.e. no borrowing of host bits. However, a network that falls within the address range of a shorter prefix will be commonly thought of as a subnet of the larger address block. Once again, actual network masks can be the same as classful addresses and subnetted classful addresses, but many classful routing protocol restrictions are eliminated.