Updated: 2021/Apr/14

NDP(8)                      System Manager's Manual                     NDP(8)

     ndp - control/diagnose IPv6 neighbor discovery protocol

     ndp [-nt] hostname
     ndp [-nt] -a | -c
     ndp [-nt] -A wait
     ndp [-nt] -d hostname
     ndp [-nt] -f filename
     ndp [-nt] -i interface [expressions ...]
     ndp [-nt] -s nodename etheraddr [temp] [proxy]

     The ndp command manipulates the address mapping table used by the
     Neighbor Discovery Protocol (NDP).

     -A wait
             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

             Expire      The time until expiry of the entry.  The entry could
                         become "permanent", in which case it will never

             S           State of the neighbor cache entry, as a single

                         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.

     -i interface [expressions ...]
             View ND information for the specified interface.  If additional
             arguments expressions are given, ndp sets 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 -foo in this case.

             nud     Turn on or off NUD (Neighbor Unreachability Detection) on
                     the interface.  NUD is usually turned on by default.
                     Specify whether or not to perform automatic link-local
                     address configuration on interface.  This flag is set by
                     net.inet6.ip6.auto_linklocal sysctl variable.
                     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.
                     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 ndp command, it is not generally
                     advisable to modify this flag manually.
                     Specify the BaseReachbleTimer on the interface in
                     Specify the RetransTimer on the interface in millisecond.
                     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 temp is given in the command.  If the word proxy
             is given, this system will act as a proxy NDP server, responding
             to requests for hostname even though the host address is not its

     -t      Print timestamp on each entry, making it possible to merge output
             with tcpdump(8).  Most useful when used with -A.

     The ndp command will exit with 0 on success, and non-zero on errors.


     The ndp command first appeared in the WIDE Hydrangea IPv6 protocol stack

NetBSD 9.99                   September 15, 2020                   NetBSD 9.99