# man > ndisc6(8)

[_NDISC6_(8)](https://www.chedong.com/phpMan.php/man/NDISC6/8/markdown)                              System Manager's Manual                             [_NDISC6_(8)](https://www.chedong.com/phpMan.php/man/NDISC6/8/markdown)

## NAME
       ndisc6 - ICMPv6 Neighbor Discovery tool

## SYNOPSIS
       **ndisc6 **[**-1mnqv**] [**-r attempts**] [**-s source_ip**] [**-w wait_ms**] <**IPv6 address**> <**iface**>


## DESCRIPTON
       **NDisc6  **is  an Unix program which implements the ICMPv6 Neighbor Discovery in userland (it is
       normally done by the kernel). It is used to lookup the link-layer address (layer  2  address,
       MAC in the case of Ethernet) of any on-link IPv6 node.

       The  IPv6 address of the node must be specified, as well as the networking interface on which
       to perform the lookup.


## OPTIONS
### -1  --single
              Exit as soon as the first advertisement is received (default).


### -h  --help
              Display some help and exit.


### -m  --multiple
              Wait for possible duplicate advertisements and print all of them.


### -n  --numeric
              If the first parameter is not a valid IPv6 address, do not try to resolve it as a  DNS
              hostname.


### -q  --quiet
              Only  display  link-layer address. Display nothing in case of failure.  That is mostly
              useful when calling the program from a shell script.


### -r attempts  --retry attempts
              Send ICMPv6 Neighbor Discovery that many times until a reply is received, or abort. By
              default, ndisc6 will try 3 times before aborting (MAX_MULTICAST_SOLICIT  and  MAX_UNI‐
              CAST_SOLICIT from RFC2461).


### -s source_ip  --source source_ip
              Specify  the IPv6 address to be used as the source for the neighbor solicitation pack‐
              ets.


### -V  --version
              Display program version and license and exit.


### -v  --verbose
              Display verbose information. That is the default.


### -w wait_ms  --wait wait_ms
              Wait _wait_ms_ milliseconds for a response before retrying.  By default, ndisc6 waits  1
              second between each attempts (RETRANS_TIMER from RFC2461).


       If  **ndisc6  **does  not receive any response after the specified number of attempts waiting for
       _wait_ms_ milliseconds each time, it will exit with code 2. On error, it  exits  with  code  1.
       Otherwise  it exits with code 0. This makes it possible to use the exit code to see if a host
       is on-link or not.


## DIAGNOSTICS
       If you get no response while you know the remote host is up, it is most likely that it is not
       on-link, that is to say, you must cross one or more routers to  reach  it.  By  design,  IPv6
       nodes ignore ICMPv6 Neighbor Discovery packets received from nodes not on the same link (i.e.
       Ethernet  segment),  for the sake of security. Technically, that is done by ensuring that the
       Hop limit (TTL) is 255.

       Note that you cannot use **ndisc6 **to lookup the local host's link-layer address.


## SECURITY
       **ndisc6 **should be _setuid_ _root_ to allow use by non-privileged users.  It  will  drop  its  root
       privileges  before any attempt is made to send or receive data from the network to reduce the
       possible impact of a security vulnerability.


## SEE ALSO
       [ping6(8)](https://www.chedong.com/phpMan.php/man/ping6/8/markdown), [rdisc6(8)](https://www.chedong.com/phpMan.php/man/rdisc6/8/markdown), [ipv6(7)](https://www.chedong.com/phpMan.php/man/ipv6/7/markdown)


## AUTHOR
       Rémi Denis-Courmont <remi at remlab dot net>

       <http://www.remlab.net/ndisc6/>

ndisc6                                         $Date$                                      [_NDISC6_(8)](https://www.chedong.com/phpMan.php/man/NDISC6/8/markdown)