ndp —
control/diagnose IPv6 neighbor discovery protocol
  
    | ndp | [ -nt]-iinterface [expressions
      ...] | 
  
    | ndp | [ -nt]-snodename etheraddr [temp]
      [proxy] | 
The ndp command manipulates the address mapping table
  used by the Neighbor Discovery Protocol (NDP).
  - -Await
- Repeat -a(dump NDP entries) every
      wait seconds.
- -a
- Dump the currently existing NDP entries. The following information will be
      printed:
    
      - Neighbor
- IPv6 address of the neighbor.
- Linklayer Address
- Linklayer address of the neighbor. It could be
          “(incomplete)” when the address
          is not available.
- Netif
- Network interface associated with the neighbor cache entry.
- Expire
- The time until expiry of the entry. The entry could become
          “permanent”, in which case it
          will never expire.
- S
- State of the neighbor cache entry, as a single letter:
        
        
          - D
- Delay
- I
- Incomplete
- N
- Nostate
- P
- Probe
- R
- Reachable
- S
- Stale
- U
- Unreachable
- W
- Waitdelete
- ?
- Unknown state (should never happen).
 
- Flags
- Flags on the neighbor cache entry, in a single letter. They are:
          Router, proxy neighbor advertisement (“p”). The field
          could be followed by a decimal number, which means the number of NS
          probes the node has sent during the current state.
 
- -c
- Erase all the NDP entries.
- -d
- Delete specified NDP entry.
- -f
- Parse the file specified by filename.
- -iinterface [expressions ...]
- View ND information for the specified interface. If additional arguments
      expressions are given, ndpsets or clears the flags or variables for the interface as specified in
      the expression. Each expression should be separated by white spaces or tab
      characters. Possible expressions are as follows. Some of the expressions
      can begin with the special character
      ‘-’, which means the flag specified
      in the expression should be cleared. Note that you need--before-fooin this
      case.
      - nud
- Turn on or off NUD (Neighbor Unreachability Detection) on the
          interface. NUD is usually turned on by default.
- auto_linklocal
- Specify whether or not to perform automatic link-local address
          configuration on interface. This flag is set by
          net.inet6.ip6.auto_linklocalsysctl
        variable.
- prefer_source
- Prefer addresses on the interface as candidates
          of the source address for outgoing packets. The default value of this
          flag is off. For more details about the entire algorithm of source
          address selection, see the IMPLEMENTATION file
          supplied with the KAME kit.
- disabled
- Disable IPv6 operation on the interface. When disabled, the interface
          discards any IPv6 packets received on or being sent to the interface
          and any IPv6 addresses on the interface are marked as
          “tentative”. When the disabled flag is cleared, DAD will
          be performed. In the sending case, an error of ENETDOWN will be
          returned to the application. This flag is typically set automatically
          in the kernel as a result of a certain failure of Duplicate Address
          Detection. While the flag can be set or cleared by hand with the
          ndpcommand, it is not generally advisable to
          modify this flag manually.
- basereachable=(number)
- Specify the BaseReachableTimer on the interface in millisecond.
- retrans=(number)
- Specify the RetransTimer on the interface in millisecond.
- curhlim=(number)
- Specify the Cur Hop Limit on the interface.
 
- -n
- Do not try to resolve numeric addresses to hostnames.
- -s
- Register an NDP entry for a node. The entry will be permanent unless the
      word tempis given in the command. If the wordproxyis given, this system will act as a proxy
      NDP server, responding to requests for hostname even
      though the host address is not its own.
- -t
- Print timestamp on each entry, making it possible to merge output with
      tcpdump(8). Most useful
      when used with -A.
Thendp command will exit with 0 on success, and
  non-zero on errors.
The ndp command first appeared in the WIDE Hydrangea
  IPv6 protocol stack kit.