Monitoring a network connection from a remote host

Sometimes you need to monitor a connection from your machine to a specific, single host or network in order to identify which network hop between your machine and the target causes trouble. You can use the following shell script to easily achieve this kind of monitoring.
If the target host is unable to respond to the specified number of ICMP packets, you will get an eMail together with a mtr to see on which hop the problem occurs.

#!/bin/bash

TARGET=8.8.8.8 # Target host or IP address to be monitored.
MAIL_RECIPIENT=you@example.com # eMail address where to send failures to.
NUMBER_OF_TEST_PACKETS=5 # Number of ICMP packets to be sent to the target. If any fails, you'll get notified.

function do_monitoring {
  ping -q -c $NUMBER_OF_TEST_PACKETS $TARGET
  status=$?
  if [ $status -ne 0 ]; then
      mail_traceroute $TARGET
  fi
  return $status
}

function mail_traceroute {
  MTR_OUTPUT=$(mtr -n -r $@)
  HOSTNAME=$(hostname -f)
  mail -s "Monitoring failure: Connection to $TARGET failed" $MAIL_RECIPIENT <<EOF
Hey,

this is $HOSTNAME calling.
I just sent $NUMBER_OF_TEST_PACKETS ICMP packets to $TARGET and that failed apparently.
Here is a traceroute to $TARGET:

$MTR_OUTPUT
EOF
}

do_monitoring

The resulting eMail looks like this:

Hey,

this is foo.example.com calling.
I just sent two ICMP packets to 1.2.3.4 and that failed apparently.
Here is a traceroute to 1.2.3.4:

HOST: foo.example.com       Loss%   Snt   Last   Avg  Best  Wrst StDev
1.|-- 10.10.13.1                 0.0%    10    0.4   0.3   0.2   0.5   0.1
2.|-- 10.179.144.1              0.0%    10    0.7   0.7   0.7   0.8   0.0
3.|-- 212.18.7.63                0.0%    10    2.2   7.0   2.1  51.0  15.4
4.|-- 194.59.190.61              0.0%    10    2.3  11.4   2.2  83.0  25.3
5.|-- 66.249.94.86               0.0%    10   26.3  13.3   9.6  29.1   7.6
6.|-- 216.239.48.117             0.0%    10   10.0  10.0  10.0  10.1   0.0
7.|-- 209.85.254.118             0.0%    10   10.0  12.7   9.8  38.1   8.9
  |  `|-- 209.85.254.112
8.|-- ???                       100.0    10    0.0   0.0   0.0   0.0   0.0
9.|-- 8.8.8.8                    0.0%    10    9.9   9.9   9.9  10.0   0.0

Keep in mind that a hop having 100% loss rate does not necessarily mean that there is trouble. You should read about how traceroute works to get an idea how to interpret it.