Cables to Go CDM-570L manual Figure A-6Default Subnet Masks for IP Classes

IP Addressing

Subnetting is required if the network is segmented.

Subnet Mask

The Subnet Mask is used by the host to determine if a destination IP address is on the local or on a remote network segment. The table in Figure A-6shows the default subnet mask used for each class of IP address.

			CLASS A
			CLASS B
			CLASS C
Address Class	Mask Decimal Value	Mask Binary Value
Class A	255.0.0.0	11111111.00000000.00000000.00000000
Class B	255.255.0.0	11111111.11111111.00000000.00000000
Class C	255.255.255.0	11111111.11111111.11111111.00000000

Figure A-6Default Subnet Masks for IP Classes

The IP address and subnet mask work with each other to identify a network element or device. The subnet mask, like an IP address, contains 4 octets sepa- rated by a dot (.) and looks similar to an IP address.

The subnet mask determines what bits in the IP address are being used to deter- mine the network ID by using the Boolean math operator and in a process called anding. Anding compares each bit value in the IP address with the bit value in the subnet mask. The result of the anding process determines which subnet the IP address is on. The Boolean and operator works as follows:

0 and 0 = 0

1 and 0 = 0

1 and 1 = 1

The table shown in Figure A-7shows the anding of two binary values and the corresponding decimal equivalents for each of the values.

Appendix A - Network Addressing A-9