Neighbor Discovery CCNA 200 301
Neighbor Discovery CCNA 200 301

IPv6 Neighbor Discovery

IPv6 Neighbor Discovery


This topic describe the operation of IPv6 neighbor discovery. Start learning CCNA 200-301 for free right now!!

Note: Welcome: This topic is part of Chapter 9 of the Cisco CCNA 1 course, for a better follow up of the course you can go to the CCNA 1 section to guide you through an order.

Video – IPv6 Neighbor Discovery

If your network is using the IPv6 communications protocol, the Neighbor Discovery protocol, or ND, is what you need to match IPv6 addresses to MAC addresses. This topic explains how ND works.

Click Play in the figure to view a demonstration of IPv6 Neighbor Discovery.

IPv6 Neighbor Discovery Messages

IPv6 Neighbor Discovery protocol is sometimes referred to as ND or NDP. In this course, we will refer to it as ND. ND provides address resolution, router discovery, and redirection services for IPv6 using ICMPv6. ICMPv6 ND uses five ICMPv6 messages to perform these services:

  • Neighbor Solicitation messages
  • Neighbor Advertisement messages
  • Router Solicitation messages
  • Router Advertisement messages
  • Redirect Message

Neighbor Solicitation and Neighbor Advertisement messages are used for device-to-device messaging such as address resolution (similar to ARP for IPv4). Devices include both host computers and routers.

Neighbor Solicitation & Neighbor Advertisemen
Neighbor Solicitation & Neighbor Advertisemen

Router Solicitation and Router Advertisement messages are for messaging between devices and routers. Typically router discovery is used for dynamic address allocation and stateless address autoconfiguration (SLAAC).

Router Solicitation & Router Advertisement
Router Solicitation & Router Advertisement

Note: The fifth ICMPv6 ND message is a redirect message which is used for better next-hop selection. This is beyond the scope of this course.

IPv6 ND is defined in the IETF RFC 4861.

IPv6 Neighbor Discovery – Address Resolution

Much like ARP for IPv4, IPv6 devices use IPv6 ND to determine the MAC address of a device that has a a known IPv6 address.

ICMPv6 Neighbor Solicitation and Neighbor Advertisement messages are used for MAC address resolution. This is similar to ARP Requests and ARP Replies used by ARP for IPv4. For example, assume PC1 wants to ping PC2 at IPv6 address 2001:db8:acad::11. To determine the MAC address for the known IPv6 address, PC1 sends an ICMPv6 Neighbor Solicitation message as illustrated in the figure.

IPv6 Neighbor Discovery Address Resolution
IPv6 Neighbor Discovery Address Resolution

ICMPv6 Neighbor Solicitation messages are sent using special Ethernet and IPv6 multicast addresses. This allows the Ethernet NIC of the receiving device to determine whether the Neighbor Solicitation message is for itself without having to send it to the operating system for processing.

PC2 replies to the request with an ICMPv6 Neighbor Advertisement message which includes its MAC address.

Packet Tracer – IPv6 Neighbor Discovery

In order for a device to communicate with another device, the MAC address of the destination device must be known. With IPv6, a process called Neighbor Discovery is responsible for determining the destination MAC address. You will gather PDU information in simulation mode to better understand the process. There is no Packet Tracer scoring for this activity.

Glossary: If you have doubts about any special term, you can consult this computer network dictionary.

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ARP CCNA 200 301