Windows Server 2012 R2 Inside Out: Networking with TCP/IP

  • 5/7/2014
Contents

Getting and using IPv4 addresses

As discussed previously, there are two categories of IPv4 addresses:

  • Public. Public addresses are assigned by Network Solutions (formerly this was InterNIC) and can also be purchased from the IANA/ICANN. Most organizations don’t need to purchase their IPv4 addresses directly, however. Instead, they get the IPv4 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 determined by their Information Technology (IT) department; in this case they request IPv4 addresses from the IT department.

IMPORTANT

Technically, if your organization doesn’t plan to connect to the Internet, you can use any IPv4 address. However, I still recommend using private IPv4 addresses in this case and taking the time to plan out the IPv4 address space carefully. If you do this and you later must connect the organization to the Internet, you won’t have to change the IPv4 address of every node on the network. Instead, you’ll need to reconfigure only the network’s Internet-facing nodes, such as a proxy server or NAT router, to connect your organization to the Internet.

Inside OUT

Public IPv4 address space

The public IPv4 address space is running out of new addresses that can be assigned to public devices (and might have run out completely by the time you read this). Whether public IPv4 addresses are exhausted for you depends on where your company is located, what regional Internet registry (RIR) is responsible for allocating IP addresses in your area of the world, and whether your Internet service provider (ISP) has any IPv4 addresses left from those it obtained from an RIR. In February 2011 the IANA/ICANN, the global authority coordinating IP addresses, ran out of new IPv4 address blocks to allocate to RIRs. Now, the RIRs themselves are running out (or have already run out) of new IPv4 addresses to assign. Because of this, if your company needs public IPv4 addresses, you might not be able to get them. In this case you need to use IPv6 for your company’s public Internet communications.

If you are planning 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 2-7.

Figure 2-7

Figure 2-7 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 IPv4 address translation using NAT. The NAT router, in turn, is connected to a firewall, and the firewall connects to the Internet. If the internal network ID is 192.168.1.0/24, the internal IPv4 addresses range from 192.168.1.1 to 192.168.1.254 and all hosts use the network mask 255.255.255.0. After this occurs, the hosts might include the following:

  • A router with IPv4 address 192.168.1.1 on the interface facing the internal network
  • A manageable switch with IPv4 address 192.168.1.2
  • Computers with IPv4 addresses 192.168.1.20 to 192.168.149
  • Servers with IPv4 addresses 192.168.1.150 to 192.168.199
  • A network printer with the IPv4 address 192.168.1.200

Follow an IPv4 addressing plan

Notice how the IPv4 addresses are assigned. I generally recommend reserving blocks of IPv4 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 IPv4 addresses 192.168.1.1 to 192.168.1.19 are reserved for network hardware, IPv4 addresses 192.168.1.20 to 192.168.1.149 are reserved for workstations, IPv4 addresses 192.168.1.150 to 192.168.1.199 are reserved for servers, and IPv4 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 IPv4 addresses you need by assessing the number of public Internet-facing nodes you need. In this example the NAT router needs a public IPv4 address, as does the external firewall. To be able to send and receive email, you’ll need an IPv4 address for the organization’s email server. To set up a public website, you’ll need an IPv4 address for the organization’s web server.

That’s a total of four IPv4 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–IPv4 address leasing fee.

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This chapter is from the book