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<h1>mmsnmptrapd message modification module</h1>
Module Name:&nbsp;&nbsp;&nbsp; imtcp
Author: Rainer Gerhards &lt;rgerhards@adiscon.com&gt; (custom-created)
Multi-Ruleset Support: since 5.8.1
Description:
This module uses a specific configuration of snmptrapd's tag values to
obtain information of the original source system and the severity present inside the
original SNMP trap. It then replaces these fields inside the syslog message.
Let's look at an example. Essentially, SNMPTT will invoke something like this: 
<pre>logger -t snmptrapd/warning/realhost Host 003c.abcd.ffff in vlan 17 is flapping between port Gi4/1 and port Gi3/2 
</pre>

This message modification module will change the tag (removing the additional information),
hostname and severity (not shown in example), so the log entry will look as follows:
<pre>
2011-04-21T16:43:09.101633+02:00 realhost snmptrapd: Host 003c.abcd.ffff in vlan 122 is flapping between port Gi4/1 and port Gi3/2 
</pre>
The following logic is applied to all message being processed:
<ol>
<li>The module checks incoming syslog entries. If their TAG field starts with "snmptrapd/"
(configurable), they are modified, otherwise not. If the are modified, this happens as follows:
<li>It will derive the hostname from the tag field which has format snmptrapd/severity/hostname 
<li>It should derive the severity from the tag field which has format
snmptrapd/severity/hostname. A configurable mapping table will be used to drive a new
severity value from that severity string. If no mapping has been defined, the original
severity is not changed.
<li>It replaces the "FromHost" value with the derived value from step2 
<li>It replaces the "Severity" value with the derived value from step 3 
</ol>
Note that the placement of this module inside the configuration is important. All actions
before this modules is called will work on the unmodified message. All messages after it's call
will work on the modified message. Please also note that there is some extra power in case it
is required: as this module is implemented via the output module interface, a filter
can be used (actually must be used) in order to tell when it is called. Usually, the catch-all
filter (*.*) is used, but more specific filters are fully supported. So it is possible to define
different parameters for this module depending on different filters. It is also possible to
just run messages from one remote system through this module, with the help of filters or
multiple rulesets and ruleset bindings. In short words, all capabilities rsyslog offers
to control output modules are also available to mmsnmptrapd.
Configuration Directives:
<ul>
<li>$mmsnmptrapdTag [tagname] 
tells the module which start string inside the tag to look for. The default is
"snmptrap/"
<li>$mmsnmptrapdSevertiyMapping [severtiymap] 
This specifies the severity mapping table. It needs to be specified as a list. Note that
due to the current config system no whitespace is supported inside the list, so be
sure not to use any whitespace inside it. 
The list is constructed of Severtiy-Name/Severity-Value pairs, delimited by comma. 
Severity-Name is a case-sensitive string, e.g. "warning" and an associated
numerical value (e.g. 4).
Possible values are in the rage 0..7 and are defined in RFC5424, table 2. The 
given sample would be specified as "warning/4". 
If multiple instances of mmsnmptrapd are used, each instance uses the most recently
defined $mmsnmptrapdSeverityMapping before itself.
</ul>
Caveats/Known Bugs:
<ul>
<li>currently none known</li>
</ul>
Example:
This enables to rewrite messages from snmptrapd and configures error and warning 
severities. The default tag is used. 

<textarea rows="10" cols="80">$ModLoad mmsnmptrapd # needs to be done just once
# ... other module loads and listener setup ...
*.* /path/to/file/with/orignalMessage # this file receives *un*modified messages
$mmsnmptrapdSeverityMapping warning/4,error/3
*.* ::mmsnmptrapd:		 # *now* message is modified
*.* /path/to/file/with/modifiedMessage # this file receives modified messages
# ... rest of config ...
</textarea>

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This documentation is part of the <a href="http://www.rsyslog.com/">rsyslog</a>
project. 
Copyright &copy; 2011 by <a href="http://www.gerhards.net/rainer">Rainer Gerhards</a> and
<a href="http://www.adiscon.com/">Adiscon</a>.
Released under the GNU GPL version 3 or higher.
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