Using Subnet Zero Subnetting with a subnet address of zero is strongly discouraged because of the problems that can arise if a network and a subnet have the same addresses. For example, if network 131.108.0.0 is subnetted as 255.255.255.0, subnet zero would be written as 131.108.0.0, which is the same as the network address. You can use the all ones subnet (131.108.255.0) and even though it is discouraged, you can enable the use of subnet zero if you need the entire subnet space for your IP address. Use the no ip subnet-zero global configuration command to restore the default and disable the use of subnet zero.
Procedure Configuring IP Unicast Routing Using Subnet Zero Command or Action Purpose Step 1 enable Example: Device>enable Enables privileged EXEC mode. Enter your password if prompted. Step 2 configure terminal Example: Device#configure terminal Enters global configuration mode. Step 3 ip subnet-zero Example: Device(config)#ip subnet-zero Enables the use of subnet zero for interface addresses and routing updates. Step 4 end Example: Device(config)#end Returns to privileged EXEC mode. Step 5 show running-config Example: Device#show running-config Verifies your entries. Step 6 copy running-config startup-config Example:
Device#copy running-config startup-config (Optional) Saves your entries in the configuration file. Configuring IP Unicast Routing 13