Chapter 14 – Analyzing IPv4 Networks

This section reviews the concepts of classful IP networks (A,B,C) 

Chapter examines how to begin with a single IP address and then determine the following facts: 

  • Class  
  • default mask 
  • number of network bits 
  • number of host bits 
  • number of host addresses in the network 
  • network ID 
  • network broadcast address 
  • first and last usable address in the network 
Table 14- 
Class 
128-191 
c 
192-223 
224-239 
240-255 
2 
IPv4 Address Classes Based on First Octet Values 
First Octet Values 
1-126 
Purpose 
Unicast (large networks) 
Unicast (medium-sized networks) 
Unicast (small networks) 
Multicast 
Reserved (formerly experimental)

IPv4 network classes and related facts: 

  • IPv4 defines five address classes 
  • three of classes (ABC) consist of unicast IP addresses.  
  • unicast addresses identify a single host or interface so that the address uniquely identifies the device in private network 
  • Class D addresses serve as multicast addresses, so that one packet sent to class D multicast IPv4 address can actually be delivered to multiple hosts 
  • Class E were intended for experimentation, but were changed to simply be reserved for future use.  
  • Class can be identified based on the value of the first octet of the address: 
Table 14-3 Key Facts for Classes A, B, and C 
First octet range 
Valid network 
numbers 
Total networks 
Hosts per network 
Octets (bits) in 
network part 
Octets (bits) in host 
part 
Default mask 
Class A 
1 - 126 
I.o.o.o - 126.0.0.0 
27-2= 126 
224-2 
3 (24) 
255.0.0.0 
Class B 
128 - 191 
128.0.0.0 - 191.255.0.0 
214 = 16,384 
216-2 
2 (16) 
2 (16) 
255.255.0.0 
Class C 
192 - 223 
192.0.0.0 - 223.255.255.0 
221 = 2,097,152 
3 (24) 
255.255.255.0

0.0.0.0 are reserved and 127.0.0.0 also 

First, Class B network numbers range from 128.0.0.0 to 191.255.0.0, for a total of 214 networks.  

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