Address Management Issues for an Internet Hosting Center

Address Management Issues for an Internet Hosting Center

An Internet hosting center is a data center that directly connects to the Internet's backbone. Space within that data center is rented to customers along with Internet connectivity. Such facilities may be owned and operated by an ISP, or they may be ISP-neutral in that they are owned by an organization that does not have its own IP backbone network. Such an organization must either engage in extensive peering relationships with ISPs (which is difficult without a backbone network) or purchase transit services from one or more ISPs. Regardless of how such a facility connects to the Internet, you would be hard-pressed to find any other environment that features as dense or complex a network as an Internet hosting facility. If nothing else, just knowing that the potential exists for hundreds or thousands of different companies to have their Web sites hosted under the same roof should tell you how extensive networking within that location can become.

A couple other attributes make Internet hosting centers worthy of separate examination with respect to managing an IP address space:

• A potentially large quantity of relatively small customer network blocks

• Extreme diversity with respect to types of network and computing products, ownership of those devices, and services supported

• Highly compartmentalized networks that are functionally specialized

Each of these attributes has a direct impact on how a network address space (or spaces) is managed within the data center. We'll take a quick look at each, as well as the peculiar challenges that each holds for a hostmaster.

Lots of "Little" Customers

A typical hosting center customer's presence might consist of half a cabinet of computers and disk drives . Of course, some customers might have several cabinets, or even several rows of cabinets , filled with equipment, but the tendency is toward smaller networks than are seen in an ISP hostmaster's job.

The relatively small size of a hosting center customer's configuration owes to the nature of services provided in such a facility. Many companies appreciate that connecting to the Internet brings a tremendous array of risks. Thus, rather than maintaining their commercial Web site at their own facility, they simply install that site in an Internet hosting center. Connectivity to and from the Internet from the organization's WAN can be made much more secure, because you can better control the inbound attempts to establish contact with hosts on that network.

An Internet hosting center also offers the subtle but significant advantage of placing Web sites right on the Internet's backbone. The alternative is to place the Web site at the edge of the Internetat the boundary between the customer WAN and the on-ramp to the Net.

The point is that the hostmaster of an Internet hosting facility is likely to be kept busy handing out lots of little address blocks. /28s through /30s are not unusual, even for large computer implementations . Such address blocks are way too small to be supported by an ISP. Consequently, even if a customer had an extra /28 or a similar- sized network, deploying it in an Internet hosting center would be futile.

The CIDR blocks assigned to customer networks would be carved from the hosting facility's larger block. That lets a single CIDR block be advertised to the Internet, as opposed to lots of little network blocks.

Highly Diverse Platforms

Given that a hosting center supports potentially hundreds of customers, you can count on each customer's having a different opinion about which are the best network and computing platforms. This hardware can be owned by the hosting facility or the customer. Customer-owned and operated equipment can be very troublesome . Because the customer is responsible for maintaining the configuration, you can't guarantee that it will subnet correctly, much less follow any of the other stability-promoting guidelines for the IP address space. Thus, you can't count on customer networks to function as expected. Worse, the problems can have an impact on the data center's network, thereby affecting other customers.

Without going into every possible scenario for problems induced by poorly managed customer networks, suffice it to say that the more homogeneous the operating environment, the more stable it can be made. Unfortunately, Internet hosting centers are anything but homogeneous.

Extreme Compartmentalization

Networks within an Internet hosting center are extremely compartmentalized. In simpler terms, there are lots of "little" networks as opposed to one large network that services the entire facility. The extreme complexity of a data center network is caused by the need to separate networks by functionally specialization as well as by ownership. For example, you can safely assume that there is a need for a "house" network that customers use to connect to the Internet. However, there might also be other networks (not connected to the house network) that are used to support backups , administrative duties , clustered computer networks, and possibly even modems or serial connections to customer WANs.

Each customer is also likely to network its own devices to support a variety of functions, including connections back to its own WAN or linking computers in a cluster. Given that each customer could have three or four different networks supporting a single Web site, and multiplying that by the hundreds of customers that could be in a hosting center, you can see how dense and compartmentalized the network environment can be! This creates the potential for confusion, because many of these back-channel networks don't bother using routable IP addresses. Instead, it is standard practice to implement RFC 1918 addresses here. That further ensures the security of such private networks. But statistically it becomes quite possible for two or more of these networks to use the same address space in the same facility. That can make troubleshooting an absolute nightmare. It also makes it absolutely essential to ensure that the back-channel networks do not become interconnected . This is also a very good reason why you should regard RFC 1918 addresses as a finite resource. You can reuse them at will, but treating them as a globally routable address space means that you avoid the confusion of duplicated address blocks on different networks within the same facility.