Overview

opEvents provides the ability for the user to set event properties as events are received. For example, if a user wanted to set a specific priority for an event it can be done here. This article will provide a methodology for adding SNMP trap parsing to EventParserRules. EventParserRules.nmis is found in the /usr/local/omk/conf directory. Read the notes at the top of this file as they are very informative as to what is possible in regard to the parser rules.

Evaluate The Traps To Be Processed

Create a list of SNMP traps that are required be processed by opEvents.

Correlate Events Into Stateful Pairs

For this discussion we will assume that the concept of 'state' is desirable. If there is a down event, there should be a corresponding up event. 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).

If any of these three event properties are not set state will not function well.

Consider a case where the element property is not set; thus being null. In this case if a 'port down' for gig0/0 was received a 'port up' for gig0/1 would clear the g0/0 'port down' event. Without the element being set opEvents cannot differentiate between interfaces.

Example parser rule for the element property.

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

Example parser rule for the stateful property

                                51 => {
                                        IF => qr/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.nmis. When parsing the traps the following properties should be extracted.

date
host
trap
details
event
element
stateful
state
priority

The install version of EventParserRules.nmis has a traplog section that will extract the date, host, trap and details fields for most situations. This article will focus 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 => qr/(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-&gt;[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.

Notice that if the author is creative and accurate with regular expressions the number of rules my be decreased.

103 => {
    IF => qr/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"

DRAFT - Methodology - opEvents EventParserRules - Adding Rules For SNMP Traps