Essential Networking Concepts: DNS, Protocols, and Addressing

Domain Name System (DNS)

The DNS defines domain addresses (made up of character strings) and converts them to binary transport addresses (IP addresses). It identifies users and computers in the network using DNS server names.

DNS is composed of a distributed database (DB) on the network. Its tables contain correspondence between domain names and IP addresses.

Types of DNS Servers

• Cache Server

  Saves name information on domains, not zones.

• Primary Server

  Obtains information for its zones from its zone files. If data needs modification in a zone, it is done on the primary server. It is undesirable to have only a single primary server, as its failure may prevent resolving requests.

• Secondary Server

  Gets information from the primary server. Secondary servers have authority over a zone. They are a "reading copy" of the zone files and must keep the information updated.

Addressing Applications at DNS

I like DNS

Transport Layer Functions

The transport layer addressing shares several connections using a single network connection (multiplexing), which reduces costs. It identifies the transport level entity, identifies communication applications, and manages the TCP and UDP protocols.

Domain Address Structure

Domain addresses form a hierarchical classification using names separated by periods (.).

• Level 1: Generic types or country codes.
• Level 2: Different organization names.
• Level 3: Subdomains within the organization specified at the second level.

Communication Port

When an application is running, control communications are sent and received through this port.

Application Services (Protocols)

• FTP (File Transfer Protocol): Used for file transfer.
• SMTP (Simple Mail Transfer Protocol): Used for email.
• HTTP (Hypertext Transfer Protocol): Used by web browsers.
• NFS (Network File System): Used for file transfer in Unix and Linux environments.

Socket Definition

A socket designates an abstraction by which two programs (possibly located on separate PCs) can exchange any data stream. This exchange is generally reliable and orderly, and the socket is defined by an IP address.

Netmask (Subnet Mask)

The netmask allows a computer or network device to determine whether data should be sent inside or outside the local network. It enables the network to be logically divided despite its physical design.

Network Protocols (ARP and RARP)

• ARP (Address Resolution Protocol): A network layer protocol responsible for finding the hardware address (MAC) corresponding to a specific IP address.
• RARP (Reverse Address Resolution Protocol): Performs the reverse function of ARP. It is used to resolve the IP address corresponding to a given hardware address (MAC).

Addresses dynamically update protocols if they are static and entered by the user.

DNS Zone Definition

The DNS model distributes domain information to DNS servers on the network. This stored information is a zone, which is defined by a set of domains and/or subdomains. The zone has authority over the domain because it maintains the information regarding the domain's organization.