Some features like SNMP, when they are working
and you've got a good management station,
it can give you a great insight to what's
going on on the network.
But when it breaks or when it's not working,
it can be frustrating.
So in this video, I'd like to recall
what we've taken a look at in the previous three or four
videos and then focus on a few of the troubleshooting
aspects regarding SNMP and what to look for in the event
that SNMP stops responding or we can't get
it working in the first place.
So let's create a list of things that can go wrong.
We'll imagine this is our SNMP server. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We'll imagine this is our SNMP server.
And we can just pick any device as an agent.
All right.
So what could go wrong?
Let's start with IP connectivity.
And including the correct ports, so UDP port 161,
and if we have traps that might be 162.
We'd want to verify that we have the IP
connectivity between the server and the agent.
We'd also make sure that both sides are configured correctly.
And if we want this agent to be able to send messages
on demand, like things that happen to send traps
or to the server, we'd want to use the command SNMP WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
or to the server, we'd want to use the command SNMP
dash server space host space.
And then the unit string or the user information
based on the version of SNMP that we're using.
That's another challenge is what version are we using?
Because if the server thinks that we're
using version three and the agent
thinks we're using version two, obviously that's
not going to work.
So we want to verify that as well.
Another aspect that can cause failures or lack of information
from moving back and forth would be the correct MIB,
or the managed device.
So the management server needs to have the appropriate MIB WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So the management server needs to have the appropriate MIB
or at least the MIB that's going to give some of the data
from that device if we want to pull and gather
that information from that device.
So having the correct MIB is also important.
Now another option is this.
What if this SNMP agent is rebooted?
Or what if we add new hardware to it?
There is interface indexes that are
associated with the interfaces on that router
or on that device.
So if we're tracking or monitoring interface index
A, for example, and then the next day
that same interface becomes interface index B, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
that same interface becomes interface index B,
the SNMP information is not going to be consistent.
So there's another command that I
would encourage you to use as well with SNMP,
and that's this one.
And that is SNMP server space IF index space persist.
And that's going to have that information we're
going to need, the index associated with the interfaces
persist even if you reboot that device
or if you add new interfaces.
Index numbers for those interfaces
are going to stay the same, which
is going to give you consistent data over time regarding
those interfaces.
So that's an important one as well.
And a lot of the troubles can come WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And a lot of the troubles can come
into place with SNMP version three simply
because there's so many options.
So if we're doing AUTH PRIV, which implies authentication
and data encryption, we want make sure
that all the settings are matched up
between the server and the agent.
That would include the passwords used for authentication
and the password used for encryption,
the method of the authentication, which
would be Shaw or MD5, the method for the encryption,
which could be AES with a key length,
or if you have an older device that's not compatible with AES, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
or if you have an older device that's not compatible with AES,
you might have to use DEZ or something less.
So you want to share all those details are in line
and synced up between the management
server and the client if you want it to work.
And a great option in troubleshooting
is to ask ourselves, when's the last time this worked?
Now if you're standing up a brand new SNMP relationship
and it's never been in place, you
might want to consider doing SNMP version two
and just verifying basic functionality
with the community strings.
And if that works, then you can tear that piece down.
And then instead replace it with the SNMP version WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And then instead replace it with the SNMP version
three with the views and the groups
and the users in those groups or access.
Because sometimes if people are implementing
SNMP version three for the first time and it's not connecting,
there are a lot of moving parts with the user pieces
and the groups and the views.
So basic functionality first with SNMP version two
is not a bad idea.
And then once you have a comfort level, yes.
Connectivity works, the basic functionality works.
And maybe when you up the ante, you
don't start with all the features of SNMP version three.
You can add the individual security pieces
for authentication and privacy for encryption one WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
for authentication and privacy for encryption one
at a time just to verify it's all going to come into place.
And one more element thing that can just bite us
is if we have an access control list that's
associated with either SNMP version
two or three on the agent, if that access control list is not
permitting the network management
server to connect to it, that's also going to prevent
successful SNMP services.
So you might want to do it without the ACL
to begin with as you're warming up to the idea
or setting up for the first time.
Then once you verify the connectivity, add the ACL, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Then once you verify the connectivity, add the ACL,
verify it still works, and then continue to build from there.
So thanks for joining me in this video about several things
that can go bump in the night regarding SNMP and how
to resolve them.
So I'll see you in the next set of videos.
Meanwhile, I hope this has been informative for you.
And I'd like to thank you for viewing.