We just learned about configuring
SNMP tags using our plug-in. Let's
now take a quick look at what really is inside the tag configuration.
In this chapter
we will not necessarily go into all the details of
manually configuring SNMP tags.
What we really want you to know is where to find the
important pieces of information and their configuration.
This could be particularly useful
when you want to edit tags after you have
imported them in Excel. A good
example would be that the IP Address of a
switch just changed. You could import the
hundreds of tags you configured for this switch into Excel.
You could then edit the tags and
re-export them after they are modified.
First of all the Pointtype.
You could use any numerical PointType. We
normally use Field32. For textural values
you could use a String Type. And
something quite interesting in SNMP is to use
Digital tags. As SNMP
agent reports statuses as
numbers. For example, a port on a switch would not
be up or down, it would simple be one
or two. This is what you get out of an
SNMP agent. So you normally create Digital
tags to associate text strings to these
numbers. You store them as
numbers, but, in our client tools, such
as ProcessBook, you see them as text.
Then you have the PointSource. As
usual, this should be the same character as you
configured in ICU to identify your interface.
Dollar Sign is the default PointSource
for the SNMP Interface. Then the two
important attributes are InstrumentTag
and the Extended Descriptor. They
contain keywords, and in some cases,
when there are multiple keywords in the same attribute,
they are separated by semicolons.
InstrumentTag contains HOST equals
and then the IP Address or the name
if the device you want to scan. The
Extended Descriptor contains the password.
CS, which stands for community string, equal,
and then the password.
Remember, in ICU there was
a parameter to tell the interface not to
read the passwords in the tags' configuration.
Rather than that, it would read the password
in a file. So you could, in
some case, omit this keyword.
The most important keyword here is
OID. This is the counter
to monitor on the device. Normally looks like
.1, .3, .6,
. and so on. Something else you can
use in the Extended Descriptor is the KEY keyword
which is used to identify the
network interface you are monitoring.
For example, on a switch you could have a port called
fastethernet4slashed4.
So using
the keyword you could tell the interface this tag
is meant to monitor this particular
port. At some point in time,
is if the OID you specified here
is not associated to the same port
on the switch anymore, the tag would not keep
collecting data. It would simple tell you
Configure. You would see this error
code in ProcessBook, for example: Configure. So you know
you have to configure it again because it's not
valid anymore.
Again, like I said a few minutes ago, we will not go
into all the details of manually configuring
SNMP tags here as there are a
multitude of different parameters you can use.
If you do want to configure them manually, we strongly
recommend your reading the associated chapter
in the SNMP Interface documentation.
What we normally do is we simply use
the plug-in. Manual configuration
is pretty useful when you want to edit a large
number of tags in Excel.
So let's keep going with other attributes.
The first Location Code, Location1,
is, as usual, the Interface ID number
as you configure it in ICU.
Location2 and Location3 here are a little bit special
in SNMP. Location2 is the
type of OID, the type of variable
you want to monitor on your device.
Is it a standard counter where
the value you get from the SNMP
agent is right away sent to PI? Or,
is this a Rate, by its In,
undefined
at the time normalized a value. A good example of
this is given at the bottom of this page.
The most popular case in which you
use a Rate is the
number of bytes going in and out of a network
interface -- a switch port for example.
You have to know that SNMP agent
will report the number of bytes in and out
as an endlessly increasing number.
So, if you record raw data out of that, you
will get a linear trend. What you have
to do when you scan a value,
you have to calculate the Rate. You
get a value, you subtract
the previous value, you divide it by the
frequency at which you scan, and it gives you the rate.
Instead of having a linear trend, you
will get a real nice looking trend like this.
This is Location2 equals one.
For any other kind of counter, you just
leave it to zero. Now,
Location3 simply determines whether the interface can
group the tag or not. Location3 set to zero
means, well, just leave this tag alone.
When you set Location3 to one,
that tells the interface, try to group this tag
with other similar tags.
Location2 and Location3
correspond to two options you have
in our plug-in to configure tags.
Let's get back to the plug-in.
And here we are, the first tab
in our SNMP Tag Configurator. You probably
remember this. You have to choose your interface
when configured in ICU,
or manually set the PointSource, the Interface
ID number, and the Scan Class. Take a look
at here, two more options here
where you have Location2.
When applicable, this plug-in will
set Location2 to one to create Rate Tags.
And here, we tell the plug-in to
create tags with Location3 equals one.
That means you tell the interface,
when you can, group tags together and make
one single call for the group of tags.
And here we have an option to
omit the Community String in the Extended Descriptor.
That means you do not put the
CS Equal. You do not write the,
the Community String, you do not write the password into the tag
configuration. That assumes
you used the option in ICU
to tell the interface to read the passwords from
a file.
Then the two last Location Codes: Location4
is, as usual, the number of the Scan Class
you want to use as configured in ICU;
and Location5, the Debugging Level.
Normally set to zero, the interface will
not write anything to the PIPC.log file.
If you are not getting the expected result out of a tag,
you could set Location5 to one, two or
three, to get more or less messages returned
to the Log File. And the last attribute
I would like to talk about is Convers,
which is a simple number to multiply
the value you got from the agent before
archiving into PI.
A good example of that would be to convert bytes into
kilobytes or megabytes.