IP Subnet Zero


When you work with classical subnetting, you always have to eliminate the subnets that contain either all zeros or all ones in the subnet portion. Hence, you always used the formula 2N 2 to define the number of valid subnets created. However, Cisco devices can use those subnets, as long as the command ip subnet-zero is in the configuration. This command is on by default in Cisco IOS Software Release 12.0 and later; if it was turned off for some reason, however, you can re-enable it by using the following command:

Router(config)#ip subnet-zero 

Now you can use the formula 2N rather than 2N 2.

2N

Number of total subnets created

 

2N 2

Number of valid subnets created

No longer needed because you have the ip subnet-zero command enabled

2H

Number of total hosts per subnet

 

2H 2

Number of valid hosts per subnet

 





CCNA Self-Study(c) CCNA Portable Command Guide
CCNA Portable Command Guide
ISBN: 1587201585
EAN: 2147483647
Year: 2006
Pages: 261
Authors: Scott Empson

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