[hobbit@sodn035u tmp]$ diff -u bbmrtg.pl.old bbmrtg.pl
--- bbmrtg.pl.old       2008-11-18 13:13:28.000000000 +0100
+++ bbmrtg.pl   2008-11-18 13:19:44.000000000 +0100
@@ -17,12 +17,21 @@
 #
 # Modified by W.J.M. Nelis, user-f4ccfde53c0d@xymon.invalid, 20080602
 # - Added scoped variable $prev
-# - Changed invokation of RRDs::fetch to use "-s $prev"
-# - MRTG recognises options "noi" and "noinfo". When checking for option "noi"
+# - Changed invocation of RRDs::fetch to use "-s $prev"
+# - MRTG recognizes options "noi" and "noinfo". When checking for option "noi"
 #   include word boundaries in the check.
 #
 # Modified by W.J.M. Nelis, user-f4ccfde53c0d@xymon.invalid, 200809
 # - Added function MyLocalTime to make a ISO8601-ish date notation
+# - Added support for checking the operational state of a link. If variable
+#   bb*chklink is defined, the value being either the ifIndex of the
+#   interface or a negative number, the status of the link becomes red
+#   if the operational state of the link is DOWN. If the value is negative,
+#   the link is considered down if no input is received, and only a little
+#   bit of output is sent.
+#   Added installation constant $GetLinkStatus.
+#   Added installation constant $ChklinkOutputThreshold.
+# - Removed trailing spaces
 #
 
 use strict;
@@ -86,6 +95,12 @@
 # Define the BACKEND MRTG is using using (RRDtool or just MRTG).
 my $BACKEND = 'RRD';  # RRD or MRTG
 
+# For the status check of a link, define the output threshold, which is not
+# exceeded by background processes, like STP and CDP, and define the command
+# to retrieve the operational status of an interface.
+my $ChklinkOutputThreshold= 125 ;      # Threshold in [B/s]
+my $GetLinkStatus= "/usr/bin/snmpget -c public -v 2c %s ifOperStatus.%d" ;
+
 # --- Start of RRDtool BACKEND settings (only used if $BACKEND = 'RRD')
 
     # Define your RRD cgi script: mrtg-rrd.cgi or 14all.cgi or routers2.cgi
@@ -206,6 +221,7 @@
                     $targetcfg{'legendo'}{$target}   || 'Out';
     my $colors    = $targetcfg{'colours'}{$target}   || 'GREEN#00eb0c,BLUE#1000ff';
     my $factor    = $targetcfg{'factor'}{$target}    || 1;
+    my $chklink   = $targetcfg{'bb*chklink'}{$target} || '' ;  # ifIndex or -1 if linkstatus check
 
     # Load MRTG parameters from "options" config line
     my $noo =
@@ -353,7 +369,7 @@
     }
 
     my ($last, $prev, $i_now, $o_now);
-        if ($BACKEND eq 'MRTG') {
+    if ($BACKEND eq 'MRTG') {
         warn "open(MRTG, '$targetLog')\n" if $tron;
         open(MRTG, $targetLog) or next;
         <MRTG>;
@@ -432,7 +448,24 @@
                     ? 'yellow' : 'green';
 __COLOR__
         }
-    } else {
+  #
+  # If symbol bb*chklink is defined, the test state becomes (also) red if the
+  # link is down. If bb*chklink is negative, the lack of both input and output
+  # is sufficient to give an alert. However, if bb*chklink is positive the
+  # operational state of the interface is checked. The value of bb*chklink
+  # is the ifIndex of the interface.
+  #
+      if ( $i_now == 0  &&  $o_now <= $ChklinkOutputThreshold  &&  $chklink ) {
+       if ( $chklink < 0 ) {
+         $color= 'red' ;               # No i/o ==> link down
+       } else {
+         my $cmd= sprintf( $GetLinkStatus, $host, $chklink ) ;
+         my $val= `$cmd` ;
+         $color= 'red'         if $val=~ m/down\(2\)/ ;
+       }  # of else
+      }  # of if
+
+   } else {
         warn "Time stamp in log is in the future by $timediff secs!\n";
         warn "Target: $target, bbfile: $bbfile\n";
         warn "current time: $current_time, last $last, stale $mrtgStaleSecs\n";
@@ -959,6 +992,18 @@
 Specifies the column in the BB display that this interface will display
 under on the alternate host.  The default value is 'mrtg'.
 
+=item B<bb*chklink[ezwf]:> <ifIndex>
+
+Specify this parameter if the operational state of the interface needs
+to be checked too. The value of the parameter is either the SNMP ifIndex
+of the interface or a negative number. If specified and the value is the
+(positive) ifIndex, the operational state of the interface is checked
+if the input rate is 0 bytes per second, and there is only a limited
+amount of output. If the interface state is DOWN, the color of the
+test will be red. If a negative value is specified, the lack of both
+input and output is sufficient to set the color of the test to red.
+The default value is not to test the operational state.
+
 =item B<bb*yellow[ezwf]:> <value>
 
 =item B<bb*red[ezwf]:> <value>