Our Values
We have already said that our system will not be connected to a public network (at least, not for the next few chapters!), so we'll use an address reserved for private networks. Figure 11.1 shows an overview of what we are trying to achieve.
Figure 11.1. The network design.
We are using a small number of machines, less than 20, so we only require a minimal number of addresses and subnets. As we stated earlier, we have decided to split the system into two subnets; the internal systems on one, and the external facing systems on the other. To make it easy for us to identify them, we will allocate the internal systems a host address between 1 and 49, and the external systems one between 50 and 99.
If we apply a supernet mask of 255.255.255.128, which is a 25-bit mask in CIDR notation, we get a subnet of 126 usable addresses, which is ample for our needs. These are shown in Table 11.9.
| Network Description | Network Address | Number of Usable Addresses | Address Range | Supernet Mask | Broadcast Address |
|---|---|---|---|---|---|
| Internal Systems | 192.168.22.0/25 | 126 | 192.168.22.1– 192.168.22.126 | 255.255.255.128 | 192.168.22.127 |
| External Systems | 192.168.44.0/25 | 126 | 192.168.44.1– 192.168.44.126 | 255.255.255.128 | 192.168.44.127 |
From this table we can see we have defined two subnets. By applying the specified supernet mask to the correct network address, we have generated a list of systems with a range of 126 addresses. Our systems will use a sequential host address, the internal ones starting from 1 and the external ones starting from 50. By combining these with the correct network address we will generate the following set of usable addresses:
192.168.22.1 to 192.168.22.49 inclusive for the internal systems
192.168.44.50 to 192.168.44.99 inclusive for the external systems
Now we have a good indication of a system's role by knowing either its network address or its host address.