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Domain Name Service (DNS)

DNS, or the Domain Name Service, provides Internet-wide conversion between IP addresses and host names. In the services file, it is called domain. The well-known port number is 53 which is where AWS gets its name for Route 53. The daemon process is called named, in.named or bind.

(TLD) Top-Level domain

A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System[1] of the Internet. The top-level domain names are installed in the root zone of the name space. For all domains in lower levels, it is the last part of the domain name, that is, the last label of a fully qualified domain name. For example, in the domain name, the top-level domain is com, or COM, as domain names are not case-sensitive. Management of most top-level domains is delegated to responsible organizations by the Internet Corporation for Assigned Names and Numbers (ICANN), which operates the Internet Assigned Numbers Authority (IANA) and is in charge of maintaining the DNS root zone.

Domain Name System (DNS)

The basic function of DNS is to resolve user-friendly domain names into IP addresses. When a client enters a fully qualified domain name (FQDN), the DNS server is queried for the IP address of the corresponding server. DNS is the tool most commonly used to find resources on large IP networks such as the Internet. While DNS has been working as the main name-resolution service on the Internet for quite some time, it does have a few weaknesses. For our discussion, we will look first at how DNS is structured, then at a few of its weak points.

Before the Internet was created, there existed a network known as the ARPAnet. This network tied together a few university and Department of Defense sites so that they could share research material. Since the network was small, each computer on the net had a small text file, known as a hosts file, that listed a user-friendly name for each host (computer) and its IP address. When another host was added to a site, the hosts file on each computer that might need to communicate with the new computer was updated with its address.
As an example, suppose that two networks were tied to this network: 1. RhinoTek and 2. Dragon Consulting
Each of these networks has five hosts that must be accessed across the network. The hosts file for each client device must include a "friendly name" and the IP address of all 10 hosts. A sample hosts file is shown in Table 3.11.

Sample Host File
Table 3.11 Sample Host File


Without DNS we would be lost in navigating websites. For many enterprises, choosing a robust DNS solution can be a challenging task. This module focuses on how to design an enterprise-friendly DNS solution using BIND. BIND is an open source DNS implementation that has become the de facto reference implementation (
(BIND) stands for Berkeley Internet Name Domain, because the software was developed at the University of California at Berkeley during the early 1980s. Currently, the Internet Systems Consortium (ISC) maintains BIND. There are two branches of BIND:
  1. one is 9.x and,
  2. 9.10.0-P2
is the current stable release in this branch.


The other branch is BIND10, release 1.2. BIND10 has, however, been renamed to Bundy ( because the ISC has concluded its work on BIND10 and is no longer updating the source pool. Because BIND 9 is much more widely used, the ISC has decided to focus on BIND 9 and not on BIND10 anymore. In this chapter we look at BIND 9.x, which is the more popular version of BIND. For an enterprise, the choice of which solution to use (BIND 9.x or BIND10) depends on whether the enterprise wants ISC support with the software. Because the ISC is focusing on BIND 9.x, and not on BIND10, 9.x might be a more suitable option if you want support from the ISC.
(DHCP) Dynamic Host Configuration Protocol is tied closely to DNS because DHCP provides network devices with an IP address, which often needs to be updated in a DNS namespace. Many enterprises use DHCP and often struggle to update DHCP-assigned IP addresses in DNS. In both cases, of DNS and DHCP, I assume you have a good understanding of how the protocol works.

[1]Domain Name System (DNS) is the backbone of the Internet.