common.sh: Created getNetworkInterface() to obtain the default route NIC

The function checks all network interface controllers (NICs) set as the
default route, using ping(1) to test them with two root servers (in case one
is off). The first NIC connected to the Internet is chosen.

Signed-off-by: Erik Alexandre Pucci <eap08@c3sl.ufpr.br>
Signed-off-by: Danilo K. S. Yorinori <danilok@c3sl.ufpr.br>

common.sh

@@ -70,3 +70,21 @@ function tryWget(){
                                      --proxy-password="${ppasswd}" \
                                      $* || return 1
 }
+
+#------------------------------------------------------------------------------
+# function: getNetworkInterface
+# Get the network interface which the client must bind to (in case there is
+# more than one default route) and the collect will use to obtain the MAC
+# address.
+function getNetworkInterface()
+{
+    interface=""
+
+    for interface in $(route | grep default | awk '{print $NF}'); do
+        # Send ICMP ECHO_REQUEST to root server I or J
+        if ping -c 1 -I ${interface} 192.36.148.17 > /dev/null 2>&1 ||
+           ping -c 1 -I ${interface} 192.58.128.30 > /dev/null 2>&1 ; then
+            break
+        fi
+    done
+}