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Chapter 25 — DHCP

A complete networking lesson based on the course chapter menu.

20 topicsPractical examplesTroubleshooting checksReview Q&A
Estimated reading time0% read

Chapter 25: DHCP

This chapter follows the topics shown in the Networking chapter menu. Work through each section in order, then use the review questions to check recall and troubleshooting reasoning.

25.1 DHCP Purpose

DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

Example: a laptop joins a LAN with no manual IP configuration. It broadcasts or multicasts the appropriate discovery traffic, receives an offer, requests the selected lease, and then applies the address, gateway, DNS settings, and lease timers.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain DHCP Purpose without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.2 DHCP DORA

DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

Example: a laptop joins a LAN with no manual IP configuration. It broadcasts or multicasts the appropriate discovery traffic, receives an offer, requests the selected lease, and then applies the address, gateway, DNS settings, and lease timers.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain DHCP DORA without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.3 Discover

Discover is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Discover in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Discover without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.4 Offer

Offer is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Offer in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Offer without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.5 Request

Request is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Request in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Request without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.6 Acknowledge

Acknowledge is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Acknowledge in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Acknowledge without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.7 UDP 67

UDP 67 identifies transport protocol UDP port 67. Port numbers identify application endpoints; a firewall or capture filter must also consider direction, state, and the complete conversation rather than the number alone.

Example: place UDP 67 in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain UDP 67 without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.8 UDP 68

UDP 68 identifies transport protocol UDP port 68. Port numbers identify application endpoints; a firewall or capture filter must also consider direction, state, and the complete conversation rather than the number alone.

Example: place UDP 68 in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain UDP 68 without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.9 DHCP Scope

DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

Example: a laptop joins a LAN with no manual IP configuration. It broadcasts or multicasts the appropriate discovery traffic, receives an offer, requests the selected lease, and then applies the address, gateway, DNS settings, and lease timers.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain DHCP Scope without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.10 DHCP Pool

DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

Example: a laptop joins a LAN with no manual IP configuration. It broadcasts or multicasts the appropriate discovery traffic, receives an offer, requests the selected lease, and then applies the address, gateway, DNS settings, and lease timers.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain DHCP Pool without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.11 Exclusions

Exclusions is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Exclusions in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Exclusions without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.12 Reservations

Reservations is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Reservations in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Reservations without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.13 Lease Duration

Lease Duration is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Lease Duration in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Lease Duration without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.14 DHCP Options

DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

Example: a laptop joins a LAN with no manual IP configuration. It broadcasts or multicasts the appropriate discovery traffic, receives an offer, requests the selected lease, and then applies the address, gateway, DNS settings, and lease timers.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain DHCP Options without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.15 Default Gateway Option

Default Gateway Option is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Default Gateway Option in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Default Gateway Option without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.16 DNS Option

DNS translates names into resource records such as IP addresses, aliases, mail-routing information, and service data. Client caching and TTL values affect how quickly changes become visible.

Example: a user can reach 203.0.113.20 but cannot reach server.example by name. That difference points toward name resolution, DNS reachability, record content, cache state, or search-suffix behavior rather than basic IP routing.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain DNS Option without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.17 DHCP Relay

DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

Example: a laptop joins a LAN with no manual IP configuration. It broadcasts or multicasts the appropriate discovery traffic, receives an offer, requests the selected lease, and then applies the address, gateway, DNS settings, and lease timers.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain DHCP Relay without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.18 Scope Exhaustion

Scope Exhaustion is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

Example: place Scope Exhaustion in a small office network containing clients, switches, a router, wireless access, DNS/DHCP services, and an internet connection. Identify which device or layer owns the function and what evidence you would inspect to verify it.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Scope Exhaustion without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.19 Rogue DHCP

DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

Example: a laptop joins a LAN with no manual IP configuration. It broadcasts or multicasts the appropriate discovery traffic, receives an offer, requests the selected lease, and then applies the address, gateway, DNS settings, and lease timers.

What to check

  • Identify which OSI/TCP-IP layer and device type are primarily responsible.
  • Check configuration, interface or service state, counters, logs, and a simple end-to-end test.
  • Verify both normal operation and one realistic failure case so you understand what changes when the feature breaks.
Practice: Practice: explain Rogue DHCP without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

25.20 DHCP Troubleshooting

DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

Example: a laptop joins a LAN with no manual IP configuration. It broadcasts or multicasts the appropriate discovery traffic, receives an offer, requests the selected lease, and then applies the address, gateway, DNS settings, and lease timers.

What to check

  • Confirm the symptom and determine whether the problem affects one host, one segment, one site, or many sites.
  • Compare actual configuration and measurements with the intended design, baseline, or documentation.
  • Change one variable at a time, verify the result, and document both the cause and the final fix.
Practice: Practice: explain DHCP Troubleshooting without reading the definition. Then draw or describe one network where it is used, name one failure symptom, and list the first two checks you would perform.

Chapter 25 Review Questions

1. What should you remember about DHCP Purpose?

Answer: DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

2. What should you remember about Discover?

Answer: Discover is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

3. What should you remember about Request?

Answer: Request is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

4. What should you remember about UDP 67?

Answer: UDP 67 identifies transport protocol UDP port 67. Port numbers identify application endpoints; a firewall or capture filter must also consider direction, state, and the complete conversation rather than the number alone.

5. What should you remember about DHCP Scope?

Answer: DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

6. What should you remember about Reservations?

Answer: Reservations is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

7. What should you remember about DHCP Options?

Answer: DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.

8. What should you remember about DNS Option?

Answer: DNS translates names into resource records such as IP addresses, aliases, mail-routing information, and service data. Client caching and TTL values affect how quickly changes become visible.

9. What should you remember about Scope Exhaustion?

Answer: Scope Exhaustion is one of the core topics in DHCP. Understand what the term represents, where it operates in the network, what information it uses, and what observable behavior confirms that it is working correctly.

10. What should you remember about DHCP Troubleshooting?

Answer: DHCP automatically supplies IP configuration such as an address, mask or prefix, gateway, DNS servers, and lease information. IPv4 clients commonly use the Discover, Offer, Request, Acknowledge exchange.