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

NAME
     ndp – control/diagnose IPv6 neighbor discovery protocol

SYNOPSIS
     ndp -a [-lntx]
     ndp -A wait [-nt]
     ndp -c [-nt]
     ndp -d [-nt] hostname
     ndp -f [-nt] filename
     ndp -H
     ndp -I [delete | interface]
     ndp -i interface [flags...]
     ndp -p
     ndp -P
     ndp -r
     ndp -R
     ndp -s [-nt] -s nodename etheraddr [temp] [proxy]

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

     -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:

                       N       Nostate
                       W       Waitdelete
                       I       Incomplete
                       R       Reachable
                       S       Stale
                       D       Delay
                       P       Probe

             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.

     -A wait
             Repeat -a (dump NDP entries) every wait seconds.

     -c      Erase all the NDP entries.

     -d      Delete specified NDP entry.

     -f filename
             Cause the file filename to be read and multiple entries to be set
             in the NDP table.  Entries in the file should be of the form

                   hostname ether_addr [temp] [proxy]

             with argument meanings as given above.  Leading whitespace and
             empty lines are ignored.  A ‘#’ character will mark the rest of
             the line as a comment.

     -H      Harmonize consistency between the routing table and the default
             router list; install the top entry of the list into the kernel
             routing table.

     -I      Shows the default interface used as the default route when there
             is no default router.

     -I interface
             Specifies the default interface used as the default route when
             there is no default router.  The interface will be used as the
             default.

     -I delete
             The current default interface will be deleted from the kernel.

     -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.

             disabled
                     Disable IPv6 operation on the interface.  When disabled,
                     the interface discards any IPv6 packets received on or
                     being sent to the interface.  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.  If the auto_linklocal per-interface flag is
                     set, automatic link-local address configuration is
                     performed again when this flag is cleared.

             proxy_prefixes
                     the interface is enabled to proxy neighbor discovery for
                     global scope prefixes matching those on link at other
                     interfaces.

             insecure do not use cryptographically generated addresses (CGA)
                     on this interface.

             replicated Address autoconfiguration proceeds under the
                     assumption that interface configuration is replicated by
                     a sleep proxy at another node on the link.  Disables
                     optimistic DAD and sends unsolicited NA with O=1 when DAD
                     completes.  Ignores DAD failures from other hardware
                     addresses.

     -l      Show link-layer reachability information.

     -n      Do not try to resolve numeric addresses to hostnames.

     -p      Show prefix list.  The following information will be printed:

             if      The network interface associated with this prefix.

             flags   The status of the prefix, expressed by a combination of
                     the following letters:

                     A       This prefix can be used for stateless address
                             autoconfiguration.
                     L, O    This prefix can be used for on-link
                             determination; that is, it can be used to
                             determine whether a given destination address is
                             on-link.
                     D       There are no reachable routers advertising this
                             prefix.

             vltime  Valid lifetime; the length of time for which the prefix
                     and a stateless autoconfigured address generated from
                     this prefix can be used for the source or destination
                     address of a packet.

             pltime  Preferred lifetime; the length of time for which the
                     prefix and a stateless autoconfigured address generated
                     from this prefix can be used by upper-layer protocols
                     unrestrictedly.

             expire  This is the remaining time that the prefix is in the
                     valid state.

             ref     The number of kernel references held for this prefix.

     -P      Flush all the entries in the prefix list.

     -r      Show default router list.

     -R      Flush all the entries in the default router list.

     -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
             own.

     -t      Print timestamp for each entry, to make it possible to merge the
             output with tcpdump(1).  Most useful when used with -A.

     -x      Show extended link-layer reachability information in addition to
             that shown by the -l flag.

     -w      Show the cryptographically generated address (CGA) parameters for
             the node.

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

SEE ALSO
     arp(8)

HISTORY
     The ndp command first appeared in WIDE Hydrangea IPv6 protocol stack kit.

macOS 15.2                       May 17, 1998                       macOS 15.2