CHAPTER 5 Networking Appliances
All the appliances described here are the building blocks of modern data centers. They enable both the establishment of network boundaries and the deployment of applications. In both physical and virtual form, they also enable Cloud Computing inasmuch as networking is its essential component.
The first critical network appliance, described in Section 5.1, is the Domain Name System (DNS) server. To access any resource on the Internet (a web page, a mailbox, a telephone to receive a call), one ultimately needs to specify an IP address of the resource. An application, however, is not supposed to know it (and rarely does). Instead, it uses a resource locator—a character string specified according to the application-layer naming scheme. The locator is then translated by the DNS into an associated IP address in real time. A few benefits of such an arrangement, beyond supporting names that are easy for humans to remember, is that it supports resource mobility and can also be utilized, in support of elasticity, for load balancing—that is, the distribution of effort among several servers that perform identical operations. But, the translation service is not the only benefit of DNS—it is also used for service discovery, which makes the DNS infrastructure particularly critical for networking and Cloud Computing.
The second appliance described in this chapter is called a firewall. Firewalls are major implements of security—particularly when it comes to network ...
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