--> Subnetting divides one large network into smaller subnets.
--> If any network is subnetted, in that the first subnet is called zero subnet and the last subnet in the subnetted network is called all one subnet.
--> For example if we subnet 192.168.1.0/24 network into 4 subnets
192.168.1.0/26
192.168.1.64/26
192.168.1.128/26
192.168.1.192/26
--> In this subnets, 192.168.1.0/26 subnet is called Zero Subnet and 192.168.1.192/26 subnet is called and all one subnet.
--> Zero Subnet is also called as All Zero Subnet. Traditionally it was recommended not to use Zero Subnet and all one subnet for addressing.
--> To increase the no of network addresses we need to include ALL ZERO subnet and ALL One Subnet in the subnetted networks for addressing.
--> IP subnet Zero command allows using first subnet and last subnet for addressing, If IP subnet zero is enabled we can use 192.168.1.0 and 192.168.1.192 networks.
If IP subnet Zero is disabled
Router(config)# no ip subnet-zero
Router(config)# interface loopback 0
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Bad mask /24 for address 192.168.1.1
If IP subnet Zero is enabled
Router(config)# ip subnet-zero
Router(config)# interface loopback 0
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)#no shutdown
Note: By default, IP subnet-zero command is enabled on IOS release 12.0 and above.
Md.Kareemoddin
CCIE# 54759
--> If any network is subnetted, in that the first subnet is called zero subnet and the last subnet in the subnetted network is called all one subnet.
--> For example if we subnet 192.168.1.0/24 network into 4 subnets
192.168.1.0/26
192.168.1.64/26
192.168.1.128/26
192.168.1.192/26
--> In this subnets, 192.168.1.0/26 subnet is called Zero Subnet and 192.168.1.192/26 subnet is called and all one subnet.
--> Zero Subnet is also called as All Zero Subnet. Traditionally it was recommended not to use Zero Subnet and all one subnet for addressing.
--> To increase the no of network addresses we need to include ALL ZERO subnet and ALL One Subnet in the subnetted networks for addressing.
--> IP subnet Zero command allows using first subnet and last subnet for addressing, If IP subnet zero is enabled we can use 192.168.1.0 and 192.168.1.192 networks.
If IP subnet Zero is disabled
Router(config)# no ip subnet-zero
Router(config)# interface loopback 0
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Bad mask /24 for address 192.168.1.1
If IP subnet Zero is enabled
Router(config)# ip subnet-zero
Router(config)# interface loopback 0
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)#no shutdown
Note: By default, IP subnet-zero command is enabled on IOS release 12.0 and above.
Md.Kareemoddin
CCIE# 54759