Extension of bbmrtg.pl: check on link down

["W.J.M. Nelis" <nelis (at) nlr.nl>]

Hello,

we are using MRTG to measure throughput connections between LAN 
equipment, and bbmrtg.pl to report the status to Hobbit / Xymon. 
bbmrtg.pl is extended to optionally check the status of a connection 
too, and report a 'red' status if the connection is down. We have found 
this a useful feature, as it detects link problems even in case 
redundancy in the network hides the problem.

bbmrtg.pl is extended to take some special action if (A) variable 
bb*chklink is defined and (B) at the same time no input is received, 
thus 0 bytes per second, and almost no output is sent. There are two 
cases: if bb*chklink is negative, this condition is sufficient to set 
the status of the connection to 'red'. If bb*chklink is positive, it is 
assumed to be the ifIndex of the interface. Using SNMP, the current 
status of the interface is retrieved. If the status is "down", the 
connection status is set to 'red'. The small amount of output allowed 
takes care of some L2 protocols which are almost always active, such as 
STP or CDP.

Note that this condition cannot be checked with the original version of 
bbmrtg.pl. That version cannot check for the condition that both input 
*and* output is (almost) zero.

Attached is the list of modifications in bbmrtg.pl.

Kind regards,
 Wim Nelis.



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[hobbit (at) 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, nelis (at) nlr.nl, 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, nelis (at) nlr.nl, 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>