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Analyzing Classful IPv4 Networks

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IP version 4 (IPv4) defines __ address classes.
host, interface
Unicast addresses identify a single __ or __ so that the address uniquely identifies the device.
Class A
Class B
Class C
Class D
Class E
Class A
Unicast (large networks)
Class B
Unicast (medium-sized networks)
Class C
Unicast (small networks)
Class D
Class E
Experimental –
Valid network numbers for Class A: –
Valid network numbers for Class B: –
Valid network numbers for Class C:
2^7 – 2 = 126
Total networks for Class A:
2^14 = 16,384
Total networks for Class B:
2^21 = 2,097,152
Total networks for Class C:
network part
The addresses in the same network have the same values in the __.
host part
The addresses in the same network have different values in the __.
default mask
Each network class has an associated __ that defines the size of the network and host parts of an unsubnetted Class A, B, and C network.
Default Mask for Class A:
Default Mask for Class B:
Default Mask for Class C:
11111111, 00000000
Decimal 255 converts to the binary value __ Decimal 0, converted to 8-bit binary, is __.
With 2 bits, you can make four combinations: 00, 01, 10, and 11. As it turns out, the total combination of unique values you can make with N bits is __.
Network number, First usable address, last usable address, Network broadcast address
Each classful network has four key numbers that describe the network:
lowest number
The network number is the numerically __ in the network.
one larger
The first (numerically lowest) host IP address is __ than the network number.
network broadcast address
The TCP/IP RFCs define a __ as a special address in each network.
network broadcast address
A __ is always the highest (last) number in the network.
one less
The highest (last) number usable as an IP address is the address that is simply __ than the network broadcast address.
network number, network broadcast address
If you can find the __ and __, finding the first and last usable IP addresses in the network is easy.
first octet
[1] Determine the class (A, B, or C) based on the __.
[2] Mentally divide the network and host octets based on the __.
host octets
[3] To find the network number, change the IP address’s __ to 0.
fourth octet of the network ID
[4] To find the first address, add 1 to the __.
[5] To find the broadcast address, change the network ID’s host octets to __.
subtract 1
[6] To find the last address, __ from the fourth octet of the network broadcast address.
0, 127
For Class A, the first odd fact is that the range of values in the first octet omits the numbers __ and __.
What would be Class A network was originally __ for some broadcasting requirements, so all addresses that begin with 0 in the first octet are __.
software testing, loopback address
What would be Class A network is still reserved because of a special address used in __, called the __ (
However, even the very first (lowest number) Class B network number (__) looks a little like a Class A network number, because it ends with three 0s.
The first octet is 128, making it a Class B network with a two-octet network part (__).
For another Class B example, the high end of the Class B range also might look strange at first glance (__), but this is indeed the numerically highest of the valid Class B network numbers.
Class A, Class B
This network’s broadcast address,, might look a little like a __ broadcast address because of the three 255s at the end, but it is indeed the broadcast address of a __ network.
128 to 191
Other valid Class B network IDs that look unusual include,,, and All of these follow the convention of a value from __ in the first octet.
Class C network __ looks a little like a Class A network because of the last three octets being 0, but because it is a Class C network, it consists of all addresses that begin with three octets equal to ***.0.0.
Class C
Other valid __ network IDs that look unusual include,,, and