152Appendix E: Understanding IP and IP addressing

Figure 29 IP addressing: class A

Base_Tel-9

Class A addresses range from 1.X.X.X to 127.X.X.X (standard network mask is 255.0.0.0). Therefore, we can have 127-2 class A networks each with 16,777,216-2 hosts (if no subnets).

 

0

 

networkid

 

 

 

 

 

 

 

 

 

hostid

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 bit

 

 

7 bits

 

 

 

 

 

 

 

 

 

 

 

24 bits

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Field subnet in table IPNETWRK

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Class A indicator

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

subnet id

 

 

 

 

 

 

hostid

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2 to 22 bits

 

 

 

 

 

 

 

2 to 22 bits

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

32 bits

For any class, the hostid can be split into a subnet id and a hostid depending on customer requirements. This helps simplify routing to areas. For class A network, the subnet id can range from 2 to 22 bits.

Note 1: Network ids and host ids which are comprised of all 1’s or all 0’s are . reserved. Therefore, subtract 2 from the subnet id and hostid to get the actual count.

Note 2: There are also special addresses that are reserved for ‘unconnected’ networks (networks that use IP but are not connected to the Internet).

Class A networks have one of these special addresses; namely 10.0.0.0.

297-8991-910 Standard 03.01 August 1999

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Cabletron Systems DMS-100 manual IP addressing class a