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Neighbor Discovery (ND)

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Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Neighbor Discovery (ND)

IPv6 Neighbor Discovery (ND) is a set of messages and processes that determine relationships between neighboring nodes. ND replaces Address Resolution Protocol (ARP), Internet Control Message Protocol (ICMP) Router Discovery, and ICMP Redirect, which are used in IPv4, and provides additional functionality. ND is described in RFC 2461, "Neighbor Discovery for IP Version 6 (IPv6)."

ND is used by hosts to:

  • Discover neighboring routers.

  • Discover addresses, address prefixes, and other configuration parameters.

ND is used by routers to:

  • Advertise their presence, host configuration parameters, and on-link prefixes.

  • Inform hosts of a better next-hop address to forward packets for a specific destination.

ND is used by nodes to:

  • Both resolve the link-layer address of a neighboring node to which an IPv6 packet is being forwarded and determine when the link-layer address of a neighboring node has changed.

  • Determine whether IPv6 packets can be sent to and received from a neighbor.

The following table lists and describes ND processes.

Process Description

Router discovery

The process by which a host discovers the local routers on an attached link (equivalent to ICMPv4 Router Discovery) and automatically configures a default router (equivalent to a default gateway in IPv4).

Prefix discovery

The process by which a host discovers the network prefixes for local destinations.

Parameter discovery

The process by which a host discovers additional operating parameters, including the link maximum transmission unit (MTU) and the default hop limit for outbound packets.

Address autoconfiguration

The process for configuring IP addresses for interfaces in either the presence or absence of a stateful address configuration server such as Dynamic Host Configuration Protocol version 6 (DHCPv6). For more information, see IPv6 address autoconfiguration.

Address resolution

The process by which a node resolves a neighboring node's IPv6 address to its link-layer address (equivalent to ARP in IPv4). The resolved link-layer address becomes an entry in a node's neighbor cache (equivalent to the ARP cache in IPv4). You can use the netsh interface ipv6 show neighbors command to view the contents of the neighbor cache on a computer running the Windows Server 2003 family and Windows XP. The neighbor cache displays the interface identifier for the neighbor cache entry, the neighboring node's IPv6 address, the corresponding link-layer address, and the state of the neighbor cache entry. For more information, see View the neighbor cache and Netsh commands for Interface IPv6.

Next-hop determination

The process by which a node determines the IPv6 address of the neighbor to which a packet is being forwarded based on the destination address. The forwarding or next-hop address is either the destination address of the packet being sent or the address of a neighboring router. The resolved next hop address for a destination becomes an entry in a node's destination cache (also known as a route cache). You can use the netsh interface ipv6 show destinationcache command to view the contents of the destination cache on a computer running the Windows Server 2003 family and Windows XP. The destination cache displays the destination address, the interface identifier and next-hop address, the interface identifier and address used as a source address when sending to the destination, and the path MTU for the destination. For more information, see View the destination cache and Netsh commands for Interface IPv6.

Neighbor unreachability detection

The process by which a node determines that IPv6 packets cannot be sent to and received from a neighboring node. After the link-layer address for a neighbor has been determined, the state of the entry in the neighbor cache is tracked. If the neighbor is no longer receiving and sending back packets, the neighbor cache entry is eventually removed. Neighbor unreachability detection provides a mechanism for IPv6 to determine that neighboring hosts or routers are no longer available on the local network segment.

Duplicate address detection

The process by which a node determines that an address considered for use is not already in use by a neighboring node (equivalent to the use of gratuitous ARP frames in IPv4).

Redirect function

The process by which a router informs a host of a better first-hop IPv6 address to reach a destination (equivalent to the function of the IPv4 ICMP Redirect message).

Note

  • IPv6 is a rapidly evolving standard. The RFCs referenced might have been made obsolete by newer RFCs.