User manual

B-10 Addressing Scheme

Supernet Example

The four networks in the example below are all connected to the

same Internet service provider (ISP). The ISP has decided to use

supernetting to reduce the size of his routing tables and

improve throughput. See Figure 6 below.

Figure 6. Sample Supernets

• Supernets 1 and 2 each require four Class C networks, so

they require a netmask with 2 zero bits (4 = 2

) in the third

octet. This yields a netmask of 255.255.252.0.

• Supernet 3 requires 7 Class C address spaces. Since 7 isn’t a

power of 2, we have to round it up to eight. This gives it a

netmask of 255.255.248.0.

• Supernet 4 is a single Class C network, making it s netmask

255.255.255.0

Now, we must assign ranges of addresses. Let’s assume that

our ISP is responsible for the network 234.170.0.0 and that his

first free addresses are at 234.170.158.0.

The third octet of Supernet 1 has to be an even multiple of 4, so

our ISP grants an address range starting at 234.170.160.0 and

hopes that the block between 158 and 160 can be filled in later.

Supernet 2 must also begin on an even multiple of 4. The first

available address after Supernet 1 conveniently fits the bill. So,

supernet 2 extends from 234.170.164.1 to 234.170.167.254.