Understanding IP class range.

[parabellum7 at yahoo.com]

Hi Keith, 

If I recall correctly, the /24 part of 192.168.0.0/24 is the subnet specified in CIDR notation (Classless Inter Domain Routing). 

Think in binary terms, that /24 equals 11111111.11111111.11111111.00000000  (note there's 24 1's) equals 255.255.255.0 so is a class C subnet with the first three octets being the network mask. 

Likewise if you had an IP addy followed by a /8 that equals 11111111.00000000.00000000.00000000 equals 255.0.0.0 so is a class A subnet. 

Called octets cuz there's 8 bits hence a decimal max of 255.

CIDR is usually seen at ISP's or in enterprise networks that need to subnet further as the network mask does not have to align with the octet boundary as it does in the classfull network addressing we're used to. That's where things get weird and all this because those silly routers only speak binary. :]

If you're seeing 192.168.0.0/24 in a zenmap target field it means scan everything from and including 192.168.0.0 to 192.168.0.255. 


IP network classes or Classfull Network Addressing

	- Range -						- mask -		# of networks	# of nodes	CIDR mask
A	1.1.1.1 - 	126.255.255.255		255.0.0.0		126				16,777,214	/8
B	128.0.0.1 - 191.255.255.255		255.255.0.0		16,384			65,534		/16
C	192.0.0.1 - 223.255.255.255		255.255.255.0	2,097,151		254			/24
D	224.0.0.1 - 239.255.255.255	
E	240.0.0.1 - 255.255.255.255



--Kenn