Getting and Using IP Addresses

As discussed previously, there are two categories of IP addresses:

  • Public Public addresses are assigned by Network Solutions (formerly this was Inter-NIC) and can be purchased as well from IANA. Most organizations don't need to purchase their IP addresses directly, however. Instead, they get the IP addresses they need from their Internet service provider (ISP).

  • Private Private addresses are reserved for Class A, B, and C networks and can be used without specific assignment. Most organizations follow the private addressing scheme as determined by their information technology (IT) department, and in which case, they would request IP addresses from the IT department.

Note

Technically, if your organization doesn't plan to connect to the Internet, you can use any IP address. However, I still recommend using private IP addresses in this case and taking the time to plan out the IP address space carefully. If you do this and you later must connect the organization to the Internet, you won't have to change the IP address of every node on the network. Instead, you'll only need to reconfigure the network's Internet-facing nodes, such as a proxy server or NAT router, to connect your organization to the Internet.

If you are planning out your organization's network infrastructure, you must determine how you want to structure the network. In many cases, you'll want to isolate the internal systems from the public Internet and place them on their own private network. An example of this is shown in Figure 24-5.

Overview diagram for connecting a private network to the Internet.

Figure 24-5. Overview diagram for connecting a private network to the Internet.

In this example, hosts on the internal network connect to a switch. The switch in turn connects to a router, which performs the necessary internal to external IP address translation using NAT. The NAT router is in turn connected to a firewall, and the firewall connects to the Internet. If the internal network ID is 192.168.1.0/24, the internal IP addresses would range from 192.168.1.1 to 192.168.1.254 and all hosts would use the network mask 255.255.255.0. After this occurs, the hosts might include the following:

  • A router with IP address 192.168.1.1 on the interface facing the internal network

  • A manageable switch with IP address 192.168.1.2

  • Computers with IP addresses 192.168.1.20 to 192.168.149

  • Servers with IP addresses 192.168.1.150 to 192.168.199

  • A network printer with the IP address 192.168.1.200

Tip

Follow an IP addressing plan

Notice how the IP addresses are assigned. I generally recommend reserving blocks of IP addresses for the various types of hosts you'll have on a network. On an internal network with the ID 192.168.1.0/24 you might designate that IP addresses 192.168.1.1 to 192.168.1.19 are reserved for network hardware, IP addresses 192.168.1.20 to 192.168.1.149 are reserved for workstations, IP addresses 192.168.1.150 to 192.168.1.199 are reserved for servers, and IP addresses above 192.168.1.200 are reserved for other types of network hardware, such as printers.

You can then determine the number of public IP addresses you need by assessing the number of public Internet-facing nodes you need. In this example, the NAT router needs a public IP address as does the external firewall. To be able to send and receive e-mail, you'll need an IP address for the organization's e-mail server. To set up a public Web site, you'll need an IP address for the organization's Web server.

That's a total of four IP addresses (six, including the network ID address and the broadcast address). In this case, your ISP might assign you a /29 subnet, giving you a total of six usable addresses. If you think you might need more than this, you could ask for a /28 subnet. However, keep in mind that you might have to pay a per–IP address leasing fee.

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset