-.\" $OpenBSD: traceroute.8,v 1.58 2014/04/27 15:30:16 jmc Exp $
+.\" $OpenBSD: traceroute.8,v 1.59 2014/04/29 17:35:29 jmc Exp $
.\" $NetBSD: traceroute.8,v 1.6 1995/10/12 03:05:50 mycroft Exp $
.\"
.\" Copyright (c) 1990, 1991, 1993
.\"
.\" @(#)traceroute.8 8.1 (Berkeley) 6/6/93
.\"
-.Dd $Mdocdate: April 27 2014 $
+.Dd $Mdocdate: April 29 2014 $
.Dt TRACEROUTE 8
.Os
.Sh NAME
.Sh DESCRIPTION
The Internet is a large and complex aggregation of
network hardware, connected together by gateways.
-Tracking the route one's packets follow (or finding the miscreant
-gateway that's discarding your packets) can be difficult.
+Tracking the route packets follow (or finding the miscreant
+gateway that's discarding packets) can be difficult.
.Nm
-utilizes the IP protocol `time to live' field and attempts to elicit an ICMP
+utilizes the IPv4 protocol time to live (TTL) field
+and attempts to elicit an ICMP
.Dv TIME_EXCEEDED
response from each gateway along the path to some
host.
+.Nm traceroute6
+does the same for the IPv6 protocol,
+instead using hop limits and ICMPv6
+.Dv TIME_EXCEEDED
+responses.
.Pp
The only mandatory parameter is the destination host name or IP number.
The default probe datagram length is 38 bytes, but this may be increased
.It Fl d
Turn on socket-level debugging.
.It Fl f Ar first_ttl
-Set the first time-to-live or hoplimit used in outgoing probe packets.
+Set the first TTL or hop limit used in outgoing probe packets.
The effect is that the first first_ttl \- 1 hosts will be skipped
in the output of
.Nm traceroute .
.It Fl I
Use ICMP or ICMP6 ECHO instead of UDP datagrams.
.It Fl l
-Display the TTL or hoplimit value of the returned packet.
+Display the TTL or hop limit value of the returned packet.
This is useful for checking for asymmetric routing.
.It Fl m Ar max_ttl
-Set the max time-to-live (max number of hops) used in outgoing probe
-packets.
+Set the maximum TTL or hop limit.
The default is the value of the system's
.Cm net.inet.ip.ttl
or
.El
.Pp
This program attempts to trace the route an IP packet would follow to some
-internet host by launching UDP probe packets with a small TTL (time to live)
+internet host by launching UDP probe packets with a small TTL
then listening for an ICMP "time exceeded" reply from a gateway.
We start out probes with a TTL of one and increase by one until we get an
ICMP "port unreachable"