Edit

Share via

NL_NEIGHBOR_STATE enumeration (nldef.h)

  • Article

The NL_NEIGHBOR_STATE enumeration type defines the state of a network layer neighbor IP address, as described in RFC 2461, section 7.3.2.

Syntax

typedef enum _NL_NEIGHBOR_STATE {
  NlnsUnreachable,
  NlnsIncomplete,
  NlnsProbe,
  NlnsDelay,
  NlnsStale,
  NlnsReachable,
  NlnsPermanent,
  NlnsMaximum
} NL_NEIGHBOR_STATE, *PNL_NEIGHBOR_STATE;

Constants

 
NlnsUnreachable
The IP address is unreachable.
NlnsIncomplete
Address resolution is in progress and the link-layer address of the neighbor has not yet been
determined. Specifically for IPv6, a Neighbor Solicitation message has been sent to the solicited-node multicast
IP address of the target, but the corresponding neighbor advertisement has not yet been received.
NlnsProbe
The neighbor is no longer known to be reachable, and probes are being sent to verify reachability.
For IPv6, a reachability confirmation is actively being sought by regularly retransmitting unicast
Neighbor Solicitation probes until a reachability confirmation is received.
NlnsDelay
The neighbor is no longer known to be reachable, and traffic has recently been sent to the
neighbor. However, instead of probing the neighbor immediately, sending probes is delayed for a short
time to give upper layer protocols an opportunity to provide reachability confirmation. For IPv6, more
time has elapsed than is specified in the
ReachabilityTime.ReachableTime member of the
MIB_IPNET_ROW2 structure since the last
positive confirmation was received that the forward path was functioning properly and a packet was sent.
If no reachability confirmation is received within a period of time (used to delay the first probe) of
entering the NlnsDelay state, a IPv6 Neighbor Solicitation (NS) message is sent, and the
State member of MIB_IPNET_ROW2 is changed to NlnsProbe.
NlnsStale
The neighbor is no longer known to be reachable, but until traffic is sent to the neighbor, no
attempt should be made to verify its reachability. For IPv6, more time has elapsed than is specified in
the
ReachabilityTime.ReachableTime member of the
MIB_IPNET_ROW2 structure since the last
positive confirmation was received that the forward path was functioning properly. While the
State member of MIB_IPNET_ROW2 is NlnsStale, no action occurs until a packet is sent. The
NlnsStale state is entered upon receiving an unsolicited neighbor discovery message that updates the
cached IP address. Receipt of such a message does not confirm reachability, and entering the NlnsStale
state insures reachability is verified quickly if the entry is actually being used. However,
reachability is not actually verified until the entry is actually used.
NlnsReachable
The neighbor is known to have been reachable recently (within tens of seconds ago). For IPv6, a
positive confirmation was received within the time that is specified in the
ReachabilityTime.ReachableTime member of the
MIB_IPNET_ROW2 structure that the forward
path to the neighbor was functioning properly. While the
State member of MIB_IPNET_ROW2 is NlnsReachable, no special action occurs as packets are
sent.
NlnsPermanent
The IP address is a permanent address.
NlnsMaximum
A maximum value for testing purposes.

Remarks

For more information about RFC 2461, section 7.3.2, see the Neighbor Discovery for IP Version 6 (IPv6) memo from Network Working Group.

Requirements

Requirement Value
Minimum supported client Available in Windows Vista and later versions of the Windows operating systems.
Header nldef.h (include Netioapi.h)

See also

MIB_IPNET_ROW2