Section: System Manager's Manual (8)
ndisc6 - ICMPv6 Neighbor Discovery tool
] [-r attempts
] [-s source_ip
] <IPv6 address
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.
- -1 or --single
Exit as soon as the first advertisement is received (default).
- -h or --help
Display some help and exit.
- -m or --multiple
Wait for possible duplicate advertisements and print all of them.
- -n or --numeric
If the first parameter is not a valid IPv6 address, do not try to
resolve it as a DNS hostname.
- -q or --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 or --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_UNICAST_SOLICIT from RFC2461).
- -s source_ip or --source source_ip
Specify the IPv6 address to be used as the source for the neighbor
- -V or --version
Display program version and license and exit.
- -v or --verbose
Display verbose information. That is the default.
- -w wait_ms or --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.
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
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.
R33mi Denis-Courmont <remi at remlab dot net>