When defining a custom mask, we always start with the default mask for the class of address that were working with. For a Class A address, the default mask is. 0. Recall that when the default subnet mask is used, it means that no subnetting is currently taking place. custom subnet mask class a IP Default Subnet Masks For Address Classes A, B and C. Table 51: Default Subnet Masks for Class A, Class B and Class C Networks. This is the default subnet mask for Class C, but can be a custom Class A with 16 bits for the subnet ID or a Class B with 8 bits for the subnet ID.
Class B Custom Subnet Mask Calculation Example. Now, let's do the same example with our Class B network (. 0) with 5 bits for the subnet ID (with a bit less narration this time; see Figure 77): Determining The Custom Subnet Mask Using Subnetting Tables. custom subnet mask class a
The last subnet is. 192 Tip: Use the custom subnet mask minus the LSB (224 32 192) Network Bits Host Bits Bit# 8 7 6 5 4 3 2 1 Value 128 64 32 16 8 4 2 1 0 0 1 1 1 1 1 0 Network Bits Host Bits Bit# 8 7 6 5 4 3 2 1 Value 128 64 32 16 8 4 2 1 1 1 0 0 0 0 0 0 But certainly custom subnets are used and even necessary when needing the use of a subnet in an increment between Class designation. The advantage is because of the need for, say, more IP addresses than a Class C at 256 (254 hosts). but you dont want a full Class Default Subnet Masks Class A. 0 Class B. 0 Class C. 0 Network. IP Addressing and Subnetting Workbooks ACLs Access Lists Workbooks VLSM VariableLength Subnet Mask Workbooks A custom subnet mask borrows bits from the host portion of the custom subnet mask class a Mar 01, 2017 Idea of building the world's most creative Staggering with construction skills of talented workers Duration: 11: 15. Home Building Art 6, 977, 110 views The subnet calculator allows a subnet ID to have its final octet equal to the final octet of its subnet mask for example, a class C network address of. 192 with a subnet mask Subnetting uses custom subnet masks instead of the default subnet masks (e. g. , using. 0 with a Class B address instead of the default. 0). When you subnet a network by using a custom mask, you can divide the IP addresses between several subnets. Figure 76: Determining The Custom Subnet Mask for A Class C Network Determine Default Subnet Mask: Each of Classes A, B and C has a default subnet mask, which is the subnet mask for the network prior to subnetting. It has a 1 for each network ID bit and a 0 for each host ID bit. For Class C, the subnet mask is. 0.