Domain Name System

1. CHAPTER 9
DOMAIN NAME SYSTEM (DNS)

2. Domain Name System (DNS)
• The Domain Name System (DNS) is the phonebook of the Internet.
• Humans access information online through domain names, like nytimes.com or
espn.com.
• Web browsers interact through Internet Protocol (IP) addresses.
• DNS translates domain names to IP addresses so browsers can load Internet
resources.
• Each device connected to the Internet has a unique IP address which other
machines use to find the device.
• DNS servers eliminate the need for humans to memorize IP addresses such as
192.168.1.1 (in IPv4), or more complex newer alphanumeric IP addresses such as
2400:cb00:2048:1::c629:d7a2 (in IPv6).

3. 9.1 INTERNET BASICS, HOST & LM HOST FILES

4. Internet Basics
• What is the Internet?
• global network of billions of computers and other electronic devices
• Global Communication
• Go online
• How does the Internet work?
• Physical cables
• Wireless
• Server
• clients

5. Host:
• A host (also known as "network host") is a computer or other device that
communicates with other hosts on a network.
• Hosts on a network include clients and servers -- that send or receive data,
services or applications.
• Hosts typically do not include intermediary network devices like switches and
routers, which are instead often categorized as nodes.
• A node is also a broader term that includes anything connected to a network,
while a host requires an IP address.
• In other words, all hosts are nodes, but network nodes are not hosts unless they
require an IP address to function.

6. LM Host file:
• (LAN Manager Hosts file) A text file in a Windows network that provides name
resolution of NetBIOS hostnames to IP addresses.
• The LMHOSTS files were the Windows counterpart to the HOSTS files in Unix, but
have long since given way to the WINS(Windows Internet Name Service) naming
system.
• LM stands for "LAN Manager," the name of Microsoft's earlier network operating
system (NOS).

7. 9.2 DNS NAMING HIERARCHY

8. • The DNS hierarchy, also called the domain name space
• Tree structure
• DNS hierarchy is comprised of the following five levels:
• Root Level Domain
• Top Level Domains (TLD)
• Second Level Domains (SLD)
• Subdomains
• Hosts

9. • Within the hierarchy, the resolution process starts at the Root Level DNS, the Top
Level DNS, working its way down to the Second Level DNS, then through any
number of sub-domains until we get to the actual hostname we want to resolve
into an IP address.

10. Root Level Domains:
• The DNS root level is the highest in the DNS hierarchy tree because it is the first
step in resolving a domain name.
• The root DNS server is the DNS for the root zone.
• It handles requests for records in the root zone and answers other requests by
providing lists of authoritative name servers for the appropriate TLD (top-level
domain).
• These are the authoritative nameservers that serve the DNS root zone. These
servers contain the global list of the top-level domains. The root zone contains
the following:
• Organizational hierarchy – such as .com, .net, .org, .edu.
• Geographic hierarchy – such as .ca, .uk, .fr, .pe.

12. Top-Level Domains:
• The next level in the DNS hierarchy is Top-Level Domains or TLDs, for short. There are over 1000
TLDs covering everything from “.abb” to “.zw” and still growing. As we have seen, the TLDs are
classified into two subcategories: organizational hierarchy and geographic hierarchy.
• The organizational hierarchy is divided into domains for the likes of commercial enterprises
(“.com”), government entities (“.gov”), educational institutions (“.edu”), and nonprofit
organizations (“.org”).
• The geographic hierarchy, meanwhile, represents the country where the domain is hosted.
Examples include “.ca” for Canada, “.uk” for the United Kingdom, “.au” for Australia, and even
“.aq” for Antarctica.
• Organizations that want to cater to their local customers can opt for TLDs that use both
organizational and geographical hierarchies. Examples would be: “.com.et” for an Ethiopian
business, “.org.al” for an organization in Albania, and “.gov.it” for the Italian government.

13. Second-Level Domains:
• A domain is a second-level domain if it is contained within a top-level domain. A
second-level domain is a label – usually, a name related to the website or the
business that owns it – immediately to the left of the top-level domain, and
separated by a dot.
• In the Domain Name System (DNS) hierarchy, a second-level domain (SLD or 2LD)
is a domain that is directly below a top-level domain (TLD). For example, in
“myexample.com”, “myexample” is the second-level domain of the “.com” TLD.

14. Subdomains:
• A subdomain – sometimes referred to as “third-level domains.” – is related to the
root domain and is denoted on the left as a second-level domain. In the URL
“blog.myexample.com” the subdomain address would be “blog.”
• Trivia: the “WWW” in www.example.com is also a sub-domain, although it isn’t
always necessary to type it in a domain name.
• Hosts:
• The host part of an FQDN is used to identify an individual device – usually a
server. In the FQDN “myserver.example.com” the hostname would be “myserver.”

15. Integration with ADS:
• If your organization already has an existing Domain Name System (DNS) Server
service, the DNS for Active Directory Domain Services (AD DS) owner must work
with the DNS owner for your organization to integrate AD DS into the existing
infrastructure.
• This involves creating a DNS server and DNS client configuration.

16. Creating a DNS server configuration:
When integrating AD DS with an existing DNS namespace, we recommend that you do the
following:
• Install the DNS Server service on every domain controller in the forest. This provides fault
tolerance if one of the DNS servers is unavailable. In this way, domain controllers do not need to
rely on other DNS servers for name resolution. This also simplifies the management environment
because all domain controllers have a uniform configuration.
• Configure the Active Directory forest root domain controller to host the DNS zone for the Active
Directory forest.
• Configure the domain controllers for each regional domain to host the DNS zones that correspond
to their Active Directory domains.
• Configure the zone containing the Active Directory forest-wide locator records to replicate to
every DNS server in the forest by using the forest-wide DNS application directory partition.

17. SRV Records:
• SRV (Service) records are custom DNS records. They are used to establish connections between a
service and a hostname.
• When an application needs to find the location of a specific service, it will search for a related SRV
record. If it finds one, it will sift through the list of services and their connecting hostnames to
find the following:
• Hostname
• Ports
• Priority and Weight
• IP Addresses, if relevant
Creating an SRV record can potentially save you time later on.

18. 9.6 FORWARDERS
• DNS Forwarding improves performance and load balances. It provides a way to
pass on namespaces or resource records that are not contained in a local Domain
Name System (DNS) server’s zone to a remote DNS server for resolution of name
queries both inside and outside a network.
• Two types- Forwarding and conditional forwarding

19. • Forwarding:
• In a simple example, a DNS forwarder sends name queries of external domains to
a remote DNS servers outside of its local network for resolution. Internal name
queries are handled by the Internal DNS server.

20. • If the DNS server has no forwarder listed for the name designated in the query, it
can attempt to resolve the query using standard recursion using root hints file.