Neighbor Discovery Protocol

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

NDP is the IPv6 Neighbor Discovery Protocol, which provides mechanisms for discovering neighboring nodes and maintaining local-link reachability information.

Neighbor Discovery Protocol (NDP) is IPv6’s replacement for ARP. It maps IPv6 Layer 3 addresses to MAC addresses and also discovers routers, link prefixes, and duplicate addresses. section 21.1 section 21.4

NDP uses ICMPv6 messages and local-link multicast for several jobs:

• Address resolution uses Neighbor Solicitation (NS, type 135) to request a MAC address and Neighbor Advertisement (NA, type 136) to return it. NS messages target the neighbor’s solicited-node multicast address rather than a broadcast. section 21.1.2
• Router discovery uses Router Solicitation (RS, type 133) sent to ff02::2 and Router Advertisement (RA, type 134), typically sent to ff02::1. section 21.1.3
• Router Advertisements provide information such as the network prefix and support Stateless Address Autoconfiguration (SLAAC), allowing a host to generate its own IPv6 address and learn a default gateway. section 21.1.3
• Duplicate Address Detection (DAD) checks whether an IPv6 address is already in use before the host uses it. section 21.4

Resolving a neighbor and verifying the result

After R1 pings R2’s IPv6 address, `show ipv6 neighbors` displays Layer 3-to-Layer 2 mappings. The output can include R2’s global and link-local addresses, the same MAC address, a REACH state, and interface Gi0/0. section 21.4

Figure 21.3 R2 uses SLAAC to generate an IPv6 address. (1) Issue the ipv6 address autoconfig command. (2) R2 sends an RS message. (3) R1 responds with an RA message. (4) R2 combines the learned prefix with a Modified EUI-64 interface ID to make its IPv6 address.

Follow the RS-to-RA exchange and see how SLAAC combines a learned prefix with a Modified EUI-64 interface identifier. section 21.1.3

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes

Explains NS, NA, RS, RA, multicast targets, SLAAC, DAD, and neighbor-table verification without detailing protocol internals.

Examples

Uses an NS/NA router exchange, Cisco IOS ping output, neighbor-table entries, and an RS/RA-based SLAAC sequence.

What it assumes

Assumes basic IPv6 addressing and IPv4 ARP concepts while contrasting their Layer 2 resolution mechanisms.

What you can do after

Operate NDP by interpreting neighbor entries, relating ICMPv6 messages to their functions, and configuring Cisco SLAAC with ipv6 address autoconfig.

How it connects

Connects IPv6, ARP, ICMPv6, multicast, SLAAC, DHCP, EUI-64, and neighbor tables.

liveBookmanning.com

Read Acing the CCNA Exam: Volume 1 Fundamentals and Protocols on liveBook Get the book at manning.com

Related concepts

• icmpv6uses · ICMPv6 is the IPv6-specific version of the Internet Control Message Protocol for communicating control, error, and diagnostic information.
• arpalternative to · The Address Resolution Protocol is a local-network protocol that maps an IPv4 address to the corresponding link-layer address, typically a MAC address.
• IPv6used by · IPv6 is the sixth version of the Internet Protocol, using 128-bit network addresses for packet-based communication.
• router discoveryimplements · Router discovery is the process by which an IPv6 host learns about available routers and related network configuration information.
• duplicate address detectionhas part · Duplicate address detection is the process of determining whether an IPv6 address is already in use on a link before assigning it to an interface.
• neighbor advertisementuses · A Neighbor Advertisement is an ICMPv6 message that communicates a neighbor's link-layer address or indicates that an IPv6 address is already in use.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 1 Fundamentals and Protocols. The section links point to the parts of the book it draws on.