traceroute6(8): Stop probing on networks rejected.

Stop probing after receiving ICMP6_DST_UNREACH and print
ICMP6 error code.

The behavior can be observed by tracing the route to,
for example, 2a02:ee80:4028:1126::

Discussed with:		Job Snijders, Nick Hilliard
Obtained from:		OpenBSD
Reviewed by:		markj, jlduran
Differential Revision:	https://reviews.freebsd.org/D47520

usr.sbin/traceroute6/traceroute6.8

@@ -27,7 +27,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd February 2, 2024
+.Dd November 12, 2024
 .Dt TRACEROUTE6 8
 .Os
 .\"
@@ -75,7 +75,7 @@
 .Sh DESCRIPTION
 The
 .Nm
-utility uses the IPv6 protocol hop limit field to elicit an ICMPv6
+utility uses the IPv6 protocol hop limit field to elicit an ICMP6
 TIME_EXCEEDED response from each gateway along the path to some host.
 .Pp
 The only mandatory parameter is the destination host name or IPv6 address.
@@ -191,6 +191,8 @@ Destination Unreachable - Not a Neighbour.
 Destination Unreachable - Address Unreachable.
 .It !H
 Parameter Problem - Unrecognized Next Header Type.
+.It !<num>
+ICMP6 unreachable code <num>.
 .It !\&
 This is printed if the hop limit is <= 1 on a port unreachable message.
 This means that the packet got to the destination, but that the reply had a hop

usr.sbin/traceroute6/traceroute6.c

@@ -1009,6 +1009,10 @@ main(int argc, char *argv[])
 								printf(" !");
 							++got_there;
 							break;
+						default:
+							++unreachable;
+							printf(" !<%d>", code & 0xff);
+							break;
 						}
 					} else if (type == ICMP6_PARAM_PROB &&
 					    code == ICMP6_PARAMPROB_NEXTHEADER) {