The Problem:
Every time I had to make a special management pack that would require data from SNMP I bumped against the SNMP table format. In my opinion the SNMP table structure isn’t very easy to read and to process in a management pack. And let me even not talk about the SNMP table indexing with a ‘foreign key’ to a other SNMP table based on the OID value and not the OID number!! This can become a nightmare for a SCOM MP developer.
So one possible solution:
First of all, this solution I am describing below was one of my first versions that where part of the prototype. Meanwhile I have updated this to more advanced/paid/production versions. Due to this I can only share the prototype code with you. This means that I changed some names and the code could be incomplete. But I am sure most of you can use this as first start.
I wanted to get the SNMP table data in a generic way so I could process it in a generic way. For example normally when you want to discover a application component based on SNMP you do a SNMP probe. But you can only generate the new component class and have to fire up a second SNMP probe to fill-in the other wanted properties. A better way would be to get all the property information in one SNMP probe. Yes off course you will use a SNMP walk probe for this. But be aware of its data returning. I can be tricky to map the SNMP data result to rows. See picture below:
So my solution was to make this simpler by reading the SNMP table walk and map it to a real table in PowerShell. Then I could manipulate this PowerShell table very simple and build up the object discovery properties or use it in monitors / rules.
The module will look like this:
Do the SNMP walk –> convert OID values it to arrays –> map the arrays to row records –> output the row records as property bag data
Very simple approach isn’t it??
So the Datamodule would look like this:
<DataSourceModuleType ID="DataSource.SNMP2Table" Accessibility="Internal" Batching="false">
<Configuration>
<xsd:element minOccurs="1" name="IP" type="xsd:string" />
<xsd:element minOccurs="1" name="CommunityString" type="xsd:string" />
<xsd:element minOccurs="1" name="Version" type="xsd:integer" />
<xsd:element minOccurs="1" name="OID" type="xsd:string" />
<xsd:element minOccurs="1" name="Walk" type="xsd:boolean" />
<xsd:element minOccurs="1" name="Root_Table_OID" type="xsd:string" />
<xsd:element minOccurs="1" name="Fields_To_Show" type="xsd:string" />
<xsd:element minOccurs="1" name="Debug" type="xsd:string" />
<xsd:element minOccurs="0" name="IntervalSeconds" type="xsd:integer" />
</Configuration>
<OverrideableParameters>
<OverrideableParameter ID="Debug" Selector="$Config/Debug$" ParameterType="string" />
<OverrideableParameter ID="IntervalSeconds" Selector="$Config/IntervalSeconds$" ParameterType="string" />
</OverrideableParameters>
<ModuleImplementation Isolation="Any">
<Composite>
<MemberModules>
<DataSource ID="get" TypeID="DataSource.SnmpGet">
<IntervalSeconds>$Config/IntervalSeconds$</IntervalSeconds>
<IP>$Config/IP$</IP>
<CommunityString>$Config/CommunityString$</CommunityString>
<Version>$Config/Version$</Version>
<SnmpVarBinds>
<SnmpVarBind>
<OID>$Config/OID$</OID>
<Syntax>1</Syntax>
<Value VariantType="8" />
</SnmpVarBind>
</SnmpVarBinds>
<Walk>$Config/Walk$</Walk>
</DataSource>
<ProbeAction ID="maptotable" TypeID="Windows!Microsoft.Windows.PowerShellPropertyBagProbe">
<ScriptName>snmp2bag.ps1</ScriptName>
<ScriptBody>
##--------------------------------------
## convert snmp table to propertie bags
##--------------------------------------
## Michel Kamp
## v1.0.2
##--------------------------------------
param ([string] $SNMP_RESULTS , [string] $Root_Table_OID , [string] $Fields_To_Show , [string] $Debug)
$guid = [guid]::NewGuid()
$Debug_File = $env:systemroot + "\temp\" + $guid + "_" + $Root_Table_OID
#$Debug_File = "c:\temp\" + $guid + "_" + $Root_Table_OID
try
{
If ($Debug -eq $true) { $SNMP_RESULTS | Out-File -FilePath ($Debug_File + "_RESULTSxml.xml") }
[xml] $data = $SNMP_RESULTS
$Root_OID = $Root_Table_OID
$OID_Fields = $Fields_To_Show.Split(",")
If ($Debug -eq $true) { $data.InnerXml | Out-File -FilePath ($Debug_File + "_Dataxml.xml") }
$api = New-Object -comObject 'Mom.ScriptAPI'
## fill the array with the SNMP vaules
$ValueArray = @{"" = ""}
$ValueArray.Clear()
foreach ( $key in $OID_Fields)
{
$ID=$key
$ValueArray.Add($ID,($data.DataItem.SnmpVarBinds.SnmpVarBind | Where-Object { $_.OID -like $Root_OID+'.'+$ID+'.*' } ))
}
# clear the debug output file
If ($Debug -eq $true) { Write-Output "PropertyBag" | Out-File -FilePath ($Debug_File + "_outputPropertyBag.xml") }
## create the propertie bags
## Loop the snmp records. First field in $OID_Fields gives the record count
for ( $x=0; $x -le ($ValueArray[$OID_Fields[0]].Count -1 ) ; $x++ )
{
$bag = $api.CreatePropertyBag()
foreach ($y in $OID_Fields)
{
$bag.AddValue("OID"+$y,$ValueArray[$y][$x].OID)
$bag.AddValue($y,$ValueArray[$y][$x].Value.InnerXml)
If ($Debug -eq $true)
{
"OID"+$y + ":" + $ValueArray[$y][$x].OID
$ValueArray[$y][$x].Value.InnerXml
$ValueArray[$y][$x].Value.InnerXml | Out-File -Append -FilePath ($Debug_File + "_outputPropertyBag.xml")
}
}
#Return bag values
$bag
}
}
# Catch all other exceptions thrown by one of those commands
catch {
If ($Debug -eq $true) { $Error | Out-File -FilePath ($Debug_File + "catch.xml") }
$Error[0]
}
## end
</ScriptBody>
<Parameters>
<Parameter>
<Name>SNMP_RESULTS</Name>
<Value>$Data$</Value>
</Parameter>
<Parameter>
<Name>Root_Table_OID</Name>
<Value>$Config/Root_Table_OID$</Value>
</Parameter>
<Parameter>
<Name>Fields_To_Show</Name>
<Value>$Config/Fields_To_Show$</Value>
</Parameter>
<Parameter>
<Name>Debug</Name>
<Value>$Config/Debug$</Value>
</Parameter>
</Parameters>
<TimeoutSeconds>900</TimeoutSeconds>
</ProbeAction>
</MemberModules>
<Composition>
<Node ID="maptotable">
<Node ID="get" />
</Node>
</Composition>
</Composite>
</ModuleImplementation>
<OutputType>System!System.PropertyBagData</OutputType>
</DataSourceModuleType>
The output data will be an Property Bag collection with one SNMP row record / property bag.
So the next part will be mapping it to discovery data. So we get this workflow:
SNMP row records prt bags –> Map to target properties –> Output target discovery Data
And again a very straight on approach.
This datamodule will look like this:
<DataSourceModuleType ID="DataSource.SNMP2Table.DiscoveryData" Accessibility="Internal" Batching="false">
<Configuration>
<IncludeSchemaTypes>
<SchemaType>System!System.Discovery.MapperSchema</SchemaType>
<SchemaType>System!System.ExpressionEvaluatorSchema</SchemaType>
</IncludeSchemaTypes>
<xsd:element minOccurs="1" name="IP" type="xsd:string" />
<xsd:element minOccurs="1" name="CommunityString" type="xsd:string" />
<xsd:element minOccurs="1" name="Version" type="xsd:integer" />
<xsd:element minOccurs="1" name="OID" type="xsd:string" />
<xsd:element minOccurs="1" name="Root_Table_OID" type="xsd:string" />
<xsd:element minOccurs="1" name="Fields_To_Show" type="xsd:string" />
<xsd:element minOccurs="1" name="InstanceSettings" type="SettingsType" />
<xsd:element minOccurs="1" name="FilterExpression" type="ExpressionType" />
<xsd:element minOccurs="1" name="FilterString" type="xsd:string" />
<xsd:element minOccurs="1" name="ClassId" type="xsd:string" />
<xsd:element minOccurs="1" name="Debug" type="xsd:string" />
<xsd:element minOccurs="0" name="IntervalSeconds" type="xsd:integer" />
</Configuration>
<OverrideableParameters>
<OverrideableParameter ID="Debug" Selector="$Config/Debug$" ParameterType="string" />
<OverrideableParameter ID="IntervalSeconds" Selector="$Config/IntervalSeconds$" ParameterType="int" />
</OverrideableParameters>
<ModuleImplementation Isolation="Any">
<Composite>
<MemberModules>
<DataSource ID="table" TypeID="DataSource.SNMP2Table">
<IP>$Config/IP$</IP>
<CommunityString>$Config/CommunityString$</CommunityString>
<Version>$Config/Version$</Version>
<OID>$Config/OID$</OID>
<Walk>true</Walk>
<Root_Table_OID>$Config/Root_Table_OID$</Root_Table_OID>
<Fields_To_Show>$Config/Fields_To_Show$</Fields_To_Show>
<Debug>$Config/Debug$</Debug>
<IntervalSeconds>$Config/IntervalSeconds$</IntervalSeconds>
</DataSource>
<ConditionDetection ID="mapfiltered" TypeID="System!System.Discovery.FilteredClassSnapshotDataMapper">
<Expression>$Config/FilterExpression$</Expression>
<ClassId>$Config/ClassId$</ClassId>
<InstanceSettings>$Config/InstanceSettings$</InstanceSettings>
</ConditionDetection>
</MemberModules>
<Composition>
<Node ID="mapfiltered">
<Node ID="table" />
</Node>
</Composition>
</Composite>
</ModuleImplementation>
<OutputType>System!System.Discovery.Data</OutputType>
</DataSourceModuleType>
At this point we have all we want to have:
1. module to get the SNMP row record table
2. Module to convert this records to discovery data
What are we missing….. yhea the top discovery rule 
This will look like :
Schedule every x minutes –> get the SNMP table as discovery data -> create the targets with filled in property values
And again the discovery rule will look like below: (remember its prototype code)
<Discovery ID="Discovery.Gateway" Enabled="true" Target="Server" ConfirmDelivery="true" Remotable="true" Priority="Normal">
<Category>Discovery</Category>
<DiscoveryTypes>
<DiscoveryClass TypeID="Gateway" />
<DiscoveryRelationship TypeID="Server2Gateway" />
</DiscoveryTypes>
<DataSource ID="getdata" TypeID="DataSource.SNMP2Table.DiscoveryData">
<IP>$Target/Property[Type="MicrosoftSystemCenterNetworkDeviceLibrary!Microsoft.SystemCenter.NetworkDevice"]/IPAddress$</IP>
<CommunityString>$Target/Property[Type="MicrosoftSystemCenterNetworkDeviceLibrary!Microsoft.SystemCenter.NetworkDevice"]/CommunityString$</CommunityString>
<Version>2</Version>
<OID>1.3.6.1.4.1.6889.2.8.1.104.6.1</OID>
<Root_Table_OID>1.3.6.1.4.1.6889.2.8.1.104.6.1</Root_Table_OID>
<Fields_To_Show>1,2,3,4,5,6,7,16,17,21,30</Fields_To_Show>
<InstanceSettings>
<Settings>
<Setting>
<Name>$MPElement[Name="MicrosoftSystemCenterNetworkDeviceLibrary!Microsoft.SystemCenter.NetworkDevice"]/IPAddress$</Name>
<Value>$Target/Property[Type="MicrosoftSystemCenterNetworkDeviceLibrary!Microsoft.SystemCenter.NetworkDevice"]/IPAddress$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="Gateway"]/Index$</Name>
<Value>$Data/Property[@Name='1']$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="Gateway"]/OID$</Name>
<Value>$Data/Property[@Name='OID1']$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="System!System.Entity"]/DisplayName$</Name>
<Value>$Data/Property[@Name='2']$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="Gateway"]/IP$</Name>
<Value>$Data/Property[@Name='4']$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="Gateway"]/MAC$</Name>
<Value>$Data/Property[@Name='5']$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="Gateway"]/Region$</Name>
<Value>$Data/Property[@Name='6']$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="Gateway"]/Location$</Name>
<Value>$Data/Property[@Name='7']$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="Gateway"]/Registered$</Name>
<Value>$Data/Property[@Name='16']$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="Gateway"]/Type$</Name>
<Value>$Data/Property[@Name='17']$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="Gateway"]/Encrypt$</Name>
<Value>$Data/Property[@Name='21']$</Value>
</Setting>
<Setting>
<Name>$MPElement[Name="Gateway"]/RecoveryRule$</Name>
<Value>$Data/Property[@Name='30']$</Value>
</Setting>
</Settings>
</InstanceSettings>
<FilterExpression>
<RegExExpression>
<ValueExpression>
<XPathQuery>/DataItem/Property[@Name='OID1']</XPathQuery>
</ValueExpression>
<Operator>MatchesRegularExpression</Operator>
<Pattern>[0-9]</Pattern>
</RegExExpression>
</FilterExpression>
<FilterString />
<ClassId>$MPElement[Name="Gateway"]$</ClassId>
<Debug>false</Debug>
<IntervalSeconds>86400</IntervalSeconds>
</DataSource>
</Discovery>
Hmm but… Yes the only values you have to specify are:
<OID>1.3.6.1.4.1.6889.2.8.1.41.6.1</OID> : This is the TOP OID of the SNMP walk. Will most of the time be the TOP OID of the SNMP table.
<Root_Table_OID>1.3.6.1.4.1.6889.2.8.1.41.6.1</Root_Table_OID> : This the table you want to convert. Will most of the time be the <OID> value.
<Fields_To_Show>1,2,3,4,5</Fields_To_Show> : This are the SNMP columns you want to get the values of.
You see very simple again. The power is in the <Fields_To_Show> parameter. You specify here the column index numbers of the values you want to use.
The value of the field number(s) specified will be returned and can be readout with $Data/Property[@Name='OIDX']$ where X is the field number. So OID1 is the g3gatewayNumber field. Use this value for the <InstanceSettings> elements.
At this point you will have a generic way to read out SNMP tables.
So…
This was the end of part 1. Reading out 1 SNMP table is not so hard to do as you have noticed. But what about reading 2 or more SNMP tables and use a ‘foreign key’ to join this SNMP tables based on the OID value (So NOT the OID key)??? Now it is becoming more interesting.. isn’t it ?? Part 2 will be all about this……
Happy Scom’ing..
Michel Kamp