Add a -D option to traceroute that prints the differences between

the probe packet we sent and the packet quoted by the ICMP response.
Can be useful for spotting hops that change the packet in-flight
or have problems generating correct ICMP responses.

MFC after:	3 weeks

1 files changed, 18 insertions, 2 deletions

diff --git a/contrib/traceroute/traceroute.8 b/contrib/traceroute/traceroute.8
index 710ecde..3592c51 100644
--- a/contrib/traceroute/traceroute.8
+++ b/contrib/traceroute/traceroute.8
@@ -24,7 +24,7 @@ traceroute \- print the route packets take to network host
 .na
 .B traceroute
 [
-.B \-deFISdnrvx
+.B \-dDeFISdnrvx
 ] [
 .B \-f
 .I first_ttl
@@ -112,6 +112,18 @@ Set the "don't fragment" bit.
 .B \-d
 Enable socket level debugging.
 .TP
+.B \-D
+When an ICMP response to our probe datagram is received,
+print the differences between the transmitted packet and
+the packet quoted by the ICMP response.
+A key showing the location of fields within the transmitted packet is printed,
+followed by the original packet in hex,
+followed by the quoted packet in hex.
+Bytes that are unchanged in the quoted packet are shown as underscores.
+Note,
+the IP checksum and the TTL of the quoted packet are not expected to match.
+By default, only one probe per hop is sent with this option.
+.TP
 .B \-g
 Specify a loose source route gateway (8 maximum).
 .TP
@@ -163,7 +175,11 @@ listening on a port in the default range, this option can be used
 to pick an unused port range.
 .TP
 .B \-q
-Set the number of probes per hop (default is 3).
+Set the number of probes per hop (default is 3,
+unless
+.B -D
+is specified,
+when it is 1).
 .TP
 .B \-r
 Bypass the normal routing tables and send directly to a host on an attached