Core Network Services

DHCP, DNS, and NAT

An overview of the essential background services that make networks easy to use, including automatic IP configuration (DHCP), name resolution (DNS), and private-to-public address translation (NAT).
Author

Chuck Nelson

Published

November 13, 2025

1 Purpose

While physical devices and logical addresses form the foundation of a network, a set of core services runs on top of this foundation to make the network functional and user-friendly. This document introduces three of the most critical network services that operate silently in the background: DHCP, DNS, and NAT. Understanding their roles is key to diagnosing many common network problems.

2 What You’ll Learn

By the end of this reading, you will be able to:

  • Explain the purpose of the Dynamic Host Configuration Protocol (DHCP) and the DORA process.
  • Describe the function of the Domain Name System (DNS) in translating domain names to IP addresses.
  • Define Network Address Translation (NAT) and explain its role in conserving IPv4 addresses and securing a private network.

This reading maps to the following program and course learning outcomes:

  • Program Learning Outcomes (PLOs):
    • 3. Apply terminology and numeric or system concepts: This document defines the functions and acronyms for the fundamental services that underpin all modern IP networks.
  • Course Learning Outcomes (CLOs):
    • 1. Identify hardware and basic network components: While these are services (software), they are integral to the function of network hardware like routers and servers.

This exercise develops the following skills, which align with the O*NET SOC Code 15-1232.00 for Computer User Support Specialists.

Learning Objective O*NET KSAs Technologies Used
Explain the function of DHCP, DNS, and NAT. Knowledge: Telecommunications, Computers & Electronics
Abilities: Information Ordering		 DHCP, DNS, NAT
Describe the DORA process for DHCP. Knowledge: Telecommunications
Skills: Reading Comprehension		 DHCP Server

3 DHCP: The Automatic Address Assigner

Imagine if you had to manually set the IP address, subnet mask, and router address for every single device that joined your network. This would be incredibly tedious and prone to error. The Dynamic Host Configuration Protocol (DHCP) solves this problem.

A DHCP server (a function often performed by the router in a small network) is responsible for automatically assigning IP addresses and other network configuration information to devices when they join the network.

3.1 The DORA Process

When a new device (a DHCP client) connects to the network, it engages in a four-step process to get an IP address, remembered by the acronym DORA:

  1. Discover: The client device sends a broadcast message across the network, essentially shouting, “Is there a DHCP server out there?”
  2. Offer: One or more DHCP servers on the network hear the broadcast and reply with an “offer” message, which includes a potential IP address, subnet mask, router (gateway) address, and DNS server addresses.
  3. Request: The client receives the offer(s) and sends a message back to the chosen server, “I would like to formally request the IP address you offered me.”
  4. Acknowledge: The DHCP server sends a final acknowledgment, “You are now officially assigned that IP address for a specific period of time (the lease time).”

This entire process happens in milliseconds, allowing for the seamless “plug-and-play” experience we are all used to.

4 DNS: The Internet’s Phone Book

It’s easy for humans to remember names like www.google.com, but computers on the internet communicate using numerical IP addresses. The Domain Name System (DNS) is the global, hierarchical system that translates human-readable domain names into machine-readable IP addresses.

4.1 How DNS Works

  1. When you type www.google.com into your browser, your computer first checks its own local cache to see if it already knows the IP address.
  2. If not, it sends a query to the DNS server that was assigned to it by DHCP.
  3. The DNS server (often run by your ISP) checks its cache. If it doesn’t have the answer, it begins a process of querying other DNS servers up the hierarchy.
  4. It starts by asking one of the global root servers, “Who knows about the .com domain?” The root server directs it to the .com top-level domain (TLD) servers.
  5. Your DNS server then asks a .com TLD server, “Who knows about the google.com domain?” The TLD server directs it to Google’s authoritative name servers.
  6. Finally, your DNS server asks Google’s name server, “What is the IP address for www.google.com?” Google’s server provides the answer (e.g., 142.250.191.78).
  7. Your DNS server sends this IP address back to your computer, which can now establish a connection with Google’s web server.

This complex process is what allows the internet to function with easy-to-remember names.

5 NAT: The Private Network Gatekeeper

As we discussed previously, there is a limited supply of public IPv4 addresses. Network Address Translation (NAT) is the technology that allows an entire private network of computers to share a single public IP address provided by the ISP. This is its primary function.

NAT is typically performed by the router.

5.1 How NAT Works

  1. Your computer, with its private IP (e.g., 192.168.1.100), wants to connect to www.google.com. It sends a packet to the router.
  2. The router receives the packet. It strips off your private IP address and replaces it with its own public IP address.
  3. Crucially, the router makes a note in its NAT table, recording that this specific conversation was initiated by 192.168.1.100.
  4. The packet travels across the internet to Google’s server. Google’s server sees the request as coming from your router’s public IP and sends its response back to that address.
  5. When the router receives the response packet from Google, it looks up the conversation in its NAT table, sees that it belongs to 192.168.1.100, and forwards the packet to your computer.

NAT also provides a basic form of security. Since the outside world only ever sees the router’s public IP address, it’s not possible for an external device to directly initiate a connection to a specific computer on your private network unless you have explicitly configured the router to allow it (a process called port forwarding).

6 Reflect and Review

ImportantReflection: 3-2-1

Now that you have reviewed this document, take a moment to reflect on your learning in your Microsoft Teams Student Notebook:

  • 3 key pieces of information a DHCP server provides to a client.
  • 2 main functions of Network Address Translation (NAT).
  • 1 question you still have about the DNS hierarchy.
TipCheck on Learning

Answer these questions in your notebook to solidify your understanding:

  1. What is the four-step process a device uses to get an IP address from a DHCP server?
  2. If you can’t browse any websites using their domain names but you can by typing in their IP addresses, which network service is likely failing?
  3. What technology allows all the devices in your home to share a single public IP address from your ISP?
  4. True or False: NAT, by its nature, prevents unsolicited incoming connections from the internet to devices on your private network.
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