What Are Three Services Provided by IPv6 Neighbor Discovery Protocol? (Choose Three.) StudyDumps Complete Breakdown
IPv6 (Internet Protocol version 6) brings a wide range of improvements over IPv4, including more efficient routing, better security, and the elimination of address exhaustion. One of the most crucial components of the IPv6 protocol suite is the Neighbor Discovery Protocol (NDP). This protocol replaces several IPv4 functions such as ARP (Address Resolution Protocol), ICMP Router Discovery, and ICMP Redirect.
When preparing for networking certification exams like CompTIA Network+, Cisco CCNA, or any IPv6-specific test, a common question you’ll encounter is:
“What are three services provided by IPv6 Neighbor Discovery Protocol? (Choose three.)”
This blog will explore the Neighbor Discovery Protocol (NDP) in depth, explain the three major services it provides, and clarify how these services contribute to the overall function and automation of IPv6 networking.
Table of Contents
What Is Neighbor Discovery Protocol (NDP) in IPv6?
Neighbor Discovery Protocol is a core mechanism in IPv6 that facilitates the communication between devices on the same local link. It uses ICMPv6 (Internet Control Message Protocol version 6) messages to manage and automate various networking tasks.
NDP allows devices to:
- Identify neighboring devices on the local link
- Determine the link-layer addresses of neighbors
- Locate routers
- Discover address prefixes
- Perform duplicate address detection (DAD)
This suite of functions makes IPv6 much more self-configuring and efficient than IPv4.
What Are Three Services Provided by IPv6 Neighbor Discovery Protocol?
Let’s now answer the core query:
What are three services provided by IPv6 Neighbor Discovery Protocol? (Choose three.)
1. Router Discovery
Router Discovery is one of the primary services provided by NDP. In IPv6, hosts don’t rely on DHCP to locate the default gateway. Instead, they use NDP to discover routers on the network.
- Routers send Router Advertisement (RA) messages periodically or in response to Router Solicitation (RS) messages from hosts.
- The RA contains important configuration details such as the default gateway, DNS info, and prefix information.
- This enables IPv6 devices to configure their IP addresses automatically using Stateless Address Autoconfiguration (SLAAC).
Why it matters: This eliminates the need for manual configuration or reliance on a DHCP server for default gateway settings.
2. Address Resolution
Address Resolution in IPv6 replaces the traditional ARP (Address Resolution Protocol) used in IPv4.
- IPv6 uses Neighbor Solicitation (NS) and Neighbor Advertisement (NA) messages to resolve IP addresses to MAC addresses.
- When a device wants to know the link-layer (MAC) address of another device on the same link, it sends an NS message to that device’s solicited-node multicast address.
- The target responds with an NA containing its MAC address.
Why it matters: This process is more secure and efficient compared to ARP and helps maintain proper local communication.
3. Neighbor Unreachability Detection (NUD)
Neighbor Unreachability Detection is a feature that ensures a node can still communicate with a neighbor.
- If a node stops receiving responses from a previously reachable neighbor, it starts sending NS messages.
- If there’s no reply within a certain number of attempts, the neighbor is marked as unreachable.
- This helps keep routing tables and caches up to date with the latest reachability status.
Why it matters: It helps maintain accurate and reliable communication paths by removing stale neighbor entries.
Additional NDP Services
While the above three services are commonly listed in exam questions, NDP offers even more:
4. Prefix Discovery
Routers advertise IPv6 address prefixes to be used for stateless address configuration. This tells hosts what range of addresses are valid on the network.
5. Parameter Discovery
This service allows routers to provide hosts with important link-specific parameters, such as MTU (Maximum Transmission Unit).
6. Redirect Function
Routers can use NDP to inform a host of a better first-hop node on the path to a destination, improving routing efficiency.
How NDP Replaces IPv4 Mechanisms
Here’s a quick comparison of how NDP replaces legacy protocols and mechanisms from IPv4:
| IPv4 Function | Replaced By in IPv6 |
| ARP | Address Resolution (via NS/NA) |
| ICMP Router Discovery | Router Discovery (via RA/RS) |
| ICMP Redirect | Redirect (via NDP) |
| DHCP (for IP/gateway) | SLAAC using RA |
| Duplicate Address Detection (via manual or DHCP) | Built into NDP |
Real-World Example of IPv6 NDP in Action
Imagine you have a laptop joining a new IPv6-enabled Wi-Fi network:
- Your laptop sends a Router Solicitation message.
- The router replies with a Router Advertisement, providing prefix and gateway information.
- Your device uses SLAAC to configure its IPv6 address.
- It performs Duplicate Address Detection to ensure the address isn’t already in use.
- It sends a Neighbor Solicitation to get the router’s MAC address.
- The router replies with a Neighbor Advertisement.
This sequence of events all occurs automatically, showing the powerful automation capabilities of NDP.
IPv6 NDP Message Types and Their Roles
| Message Type | Description |
| Router Solicitation (RS) | Sent by hosts to prompt Router Advertisements |
| Router Advertisement (RA) | Sent by routers to advertise presence and configuration |
| Neighbor Solicitation (NS) | Used for address resolution and reachability checks |
| Neighbor Advertisement (NA) | Sent in response to NS messages |
| Redirect | Informs host of a better next-hop router |
Why Understanding NDP Matters for Certification Exams
If you’re studying for certification exams like CCNA, CompTIA Network+, or Cisco DevNet, understanding how IPv6 operates is non-negotiable. Questions based on NDP—like “What are three services provided by IPv6 Neighbor Discovery Protocol? (Choose three.)”—test your ability to understand real-world networking behavior.
NDP is central to IPv6 communication. It replaces several IPv4 protocols, improves automation, and supports scalable, self-configuring networks—key features every network engineer must master.
Final Thoughts
The IPv6 Neighbor Discovery Protocol (NDP) is essential for seamless communication in IPv6-enabled networks. It automates several critical networking functions that once required manual setup or additional protocols in IPv4.
To summarize, the three core services provided by IPv6 NDP are:
- Router Discovery
- Address Resolution
- Neighbor Unreachability Detection
Understanding how these services work and interact is essential for configuring and troubleshooting IPv6 networks and pasing network certification exams.
Sample Multiple Choice Questions (MCQs)
Question 1
What are three services provided by IPv6 Neighbor Discovery Protocol? (Choose three.)
A. Router Discovery
B. IPsec Configuration
C. Address Resolution
D. Neighbor Unreachability Detection
E. DNS Resolution
Correct Answers: A, C, D
Question 2
Which NDP message is used by a host to learn the MAC address of a neighboring device?
A. Router Advertisement
B. Neighbor Solicitation
C. Redirect
D. ICMP Echo Request
Correct Answer: B
Question 3
What does the Neighbor Unreachability Detection mechanism ensure?
A. That routing loops are avoided
B. That a neighbor is still reachable
C. That DNS services are operational
D. That SLAAC is successful
Correct Answer: B
Question 4
Which NDP message helps a router inform a host of a better first-hop router for a destination?
A. Neighbor Advertisement
B. Router Solicitation
C. Redirect
D. Address Resolution
Correct Answer: C
