Overview

opEvents provides the ability for the adminstrator to customise an event's properties from a variety of inputs. For example, if a user wanted to set a specific priority for an event it can be done during the input parsing stages.  This article will provide a methodology for adding SNMP trap parsing to EventParserRules.

Define The Traps that Will Be Processed

creating events from SNMP traps, via a generic extensible parser with EventParserRules.

The generic parser rules are defined in EventParserRules.json which  is found in the configuration directory /usr/local/omk/conf.  Please read the notes at the top of this file first as they are very informative as to what is possible in regard to the parser rules.

Evaluate The Traps To Be Processed

Create The customer should provide a list of SNMP traps that they require are required be processed by opEvents. 

Correlate Events Into Stateful Pairs

For this discussion we will assume that the concept of 'state' is important to the customerdesirable.  i.e. If there is a "down" event, there should be a corresponding "up" event.  , and opEvents should keep track of the state and ignore duplicate inputs. (It is possible that several "down" events could share a single "up" or clearing event.)

State

opEvents tracks state based on a tuple of three event properties.

• node
• element
• stateful

This is a critical concept.  The node property will always be the same for any given node.  The element property will be somewhat dynamic, usually a regular expression will parse and 'capture' it.  The most comment element example would be an interface; gig0/0 versus gig0/1.  The stateful property is necessary because the same element may have different events; consider an interface down event versus an OSPF event on the same element (gig0/0).

Example parser rule for the element property.

            "53" : {
               "IF" : "IF-MIB::ifIndex\\.\\d+=(\\d+)",
               "THEN" : [
                  "capture(element)"
               ]
            },

Example parser rule for the stateful property

            "51" : {
               "IF" : "IF-MIB::linkDown",
               "THEN" : [
                  "set.event(Interface Down)",
                  "set.stateful(Interface)",
                  "set.state(down)",
                  "set.priority(3)"
               ]
            },

Create Parser Rules

opEvents will process the trap log file as specified on opCommon.nmisjson.  When parsing the traps, at least the following properties should be extracted.:

• date
• host
• trap
• details
• event
• element
• stateful
• state
• priority

The install shipped version of of EventParserRules.nmis has json has a traplog section that will extract the date, host, trap and details fields for most situations. 

This article will focus focuses on situations where customers want customization for the remaining fields.

Set the Element

Review all the SNMP traps to determine which OID best describes what will become the element property.  Write a regular expression that matches this.

### This is observed the trap opEvents is receiving, and 
### is the best candidate to become the element property:

STARENT-MIB::starSlotNum=6

### Refering to the vendors mib file starSlotNum is found:

starSlotNum OBJECT-TYPE
    SYNTAX  Integer32(1..48)
    MAX-ACCESS  accessible-for-notify
    STATUS  current
    DESCRIPTION
        "The slot number"
    ::= { starSlotEntry 1 }

Based on this we can write the regular expression to set the element.

"2": {  
	"DESCRIPTION": "Set element for card number.",
    "IF": "(STARENT-MIB::starSlotNum=\d+)",
    "THEN": ["capture(element)"]
},

Notice the regular expression will catch an number of digits following the '=' character.  This rule 'captures' the element.  In this way we can dynamically assign event properties based on a regular expression.

Set Other Properties

Generally the other properties that we wish to set can be done with one rule. Consider the following trap received by opEvents.

2017-07-12T12:23:37   10.113.176.4    UDP: [10.113.176.4]:36570->[10.255.26.7]       
SNMPv2-MIB::sysUpTime.0=6:1:04:53.72    
SNMPv2-MIB::snmpTrapOID.0=STARENT-MIB::starCardTempOK   
STARENT-MIB::starSlotNum=1        
STARENT-MIB::starCardTemperature=40 degrees Celcius     
SNMPv2-MIB::snmpTrapEnterprise.0=STARENT-MIB::starentTraps

Evaluating this trap it's determined that a single rule can set the properties below. 

"103": {
    "IF": "STARENT-MIB::starCardTempOK",
    "THEN": [
      "set.event(Card Temperature OK)", 
      "set.stateful(temperature)", 
      "set.state(up)", 
      "set.priority(2)"
    ]
},

Based on a match of "STARENT-MIB::starCardTempOK", the rule will take action.

• event - "Card Temperature OK"
• stateful - "temperature"
• state - "up"
• priority - "2"