Operation Manual – IP Address-IP Performance-IPXH3C S7500 Series Ethernet Switches Chapter 1 IP Address Configuration1-31.1.2 Subnet and MaskThe traditional IP address classification method wastes IP addresses greatly. In orderto make full use of the available IP addresses, the concepts of mask and subnet wereintroduced.A mask is a 32-bit number corresponding to an IP address. The number consists of 1sand 0s. A mask is defined as follows: the bits of the network number and subnetnumber are set to 1, and the bits of the host number are set to 0. The mask divides anIP address into two parts: subnet address and host address. In an IP address, the partcorresponding to the "1" bits in the mask is the subnet address, and the partcorresponding to the remaining "0" bits in the mask is the host address. If there is nosubnet division, the subnet mask uses the default value and the length of 1s in themask is equal to the net-id length. Therefore, for IP addresses of classes A, B and C,the default values of the corresponding subnet masks are 255.0.0.0, 255.255.0.0 and255.255.255.0 respectively.The mask can be used to divide a Class A network containing more than 16,000,000hosts or a Class B network containing more than 60,000 hosts into multiple smallnetworks. Each small network is called a subnet. For example, for the Class B networkaddress 138.38.0.0, the mask 255.255.224.0 can be used to divide the network intoeight subnets: 138.38.0.0, 138.38.32.0, 138.38.64.0, 138.38.96.0, 138.38.128.0,138.38.160.0, 138.38.192.0 and 138.38.224.0 (see Figure 1-2). Each subnet cancontain more than 8,000 hosts.10001010, 00100110, 000 00000, 000000ClassB138.38.0.0Subnet mask255.255.224.00011111111, 11111111, 111 00000, 0000000011111111, 11111111, 000 00000, 000000Standardmask255.255.0.0Subnet address:00000 Subnet address: 138 .3 8. 0. 0001 Subnet address: 138 .3 8. 32. 0010 Subnet address: 138 .3 8. 64. 0011 Subnet address: 138 .3 8. 96. 0100 Subnet address: 138 .3 8.1 28. 0101 Subnet address: 138 .3 8.1 60. 0110 Subnet address: 138 .3 8.1 92. 0111 Subnet address: 138 .3 8.2 24. 0Sub netnumbe r HostnumberSubnet address:10001010, 00100110, 000 00000, 000000ClassB138.38.0.0Subnet mask255.255.224.00011111111, 11111111, 111 00000, 0000000011111111, 11111111, 000 00000, 000000Standardmask255.255.0.0Subnet address:00000 Subnet address: 138 .3 8. 0. 0001 Subnet address: 138 .3 8. 32. 0010 Subnet address: 138 .3 8. 64. 0011 Subnet address: 138 .3 8. 96. 0100 Subnet address: 138 .3 8.1 28. 0101 Subnet address: 138 .3 8.1 60. 0110 Subnet address: 138 .3 8.1 92. 0111 Subnet address: 138 .3 8.2 24. 0Sub netnumbe r HostnumberSubnet address:10001010, 00100110, 000 00000, 000000ClassB138.38.0.0Subnet mask255.255.224.00011111111, 11111111, 111 00000, 0000000011111111, 11111111, 000 00000, 000000Standardmask255.255.0.0Subnet address:00000 Subnet address: 138 .3 8. 0. 0001 Subnet address: 138 .3 8. 32. 0010 Subnet address: 138 .3 8. 64. 0011 Subnet address: 138 .3 8. 96. 0100 Subnet address: 138 .3 8.1 28. 0101 Subnet address: 138 .3 8.1 60. 0110 Subnet address: 138 .3 8.1 92. 0111 Subnet address: 138 .3 8.2 24. 0Sub netnumbe r HostnumberSubnet address:10001010, 00100110, 000 00000, 000000ClassB138.38.0.0Subnet mask255.255.224.00011111111, 11111111, 111 00000, 0000000011111111, 11111111, 000 00000, 000000Standardmask255.255.0.0Subnet address:00000 Subnet address: 138 .3 8. 0. 0001 Subnet address: 138 .3 8. 32. 0010 Subnet address: 138 .3 8. 64. 0011 Subnet address: 138 .3 8. 96. 0100 Subnet address: 138 .3 8.1 28. 0101 Subnet address: 138 .3 8.1 60. 0110 Subnet address: 138 .3 8.1 92. 0111 Subnet address: 138 .3 8.2 24. 0Sub netnumbe r Hostnumber11111111, 11111111, 111 00000, 0000000011111111, 11111111, 000 00000, 000000Standardmask255.255.0.0Subnet address:00000 Subnet address: 138 .3 8. 0. 0001 Subnet address: 138 .3 8. 32. 0010 Subnet address: 138 .3 8. 64. 0011 Subnet address: 138 .3 8. 96. 0100 Subnet address: 138 .3 8.1 28. 0101 Subnet address: 138 .3 8.1 60. 0110 Subnet address: 138 .3 8.1 92. 0111 Subnet address: 138 .3 8.2 24. 0Sub netnumbe r HostnumberSubnet address:Figure 1-2 Subnet division of the IP address1.2 Configuring IP Address(es) for a VLAN InterfaceYou can only configure an IP address for the VLAN interface using a correspondingcommand. Generally, it is enough to configure one IP address for a VLAN interface.
