SNMP exercises

Introduction

Goals

Install and learn to use the SNMP commands
Explore and identify standard vs enterprise parts of the MIB tree
Install vendor specific MIBs and use those with the SNMP commands

Notes

Commands preceded with "$" imply that you should execute the command as a general user - not as root.
Commands preceded with "#" imply that you should be working as root.
Commands with more specific command lines (e.g. "rtrX>" or "mysql>") imply that you are executing commands on remote equipment, or within another program.

Installing client (manager) tools

Start by installing the net-snmp tools:

$ sudo apt-get install snmp
$ sudo apt-get install snmp-mibs-downloader

The second of the two commands downloads the standard IETF and IANA SNMP MIBs which are not included by default.

Note: for this to work, you must enable the "multiverse" source in your APT configuration, If you are using Ubuntu 12.04 or 14.04. This has already been done for you in this workshop.

Now, edit the file /etc/snmp/snmp.conf:

$ sudo editor /etc/snmp/snmp.conf

Change this line:

mibs :

... so that it looks like:

# mibs :

(You are "commenting out" the empty mibs statement, which was telling the snmp* tools not to automatically load the mibs in the /usr/share/mibs/ directory)

Now, make your own copy of the file /etc/snmp/snmp.conf, make it readable only by you, and add your credentials to it:

$ cd
$ mkdir .snmp
$ cp /etc/snmp/snmp.conf .snmp/
$ chmod 700 .snmp/
$ sudo editor .snmp/snmp.conf

Add the following lines to the bottom:

defVersion 3
defCommunity NetManage
defSecurityName admin
defSecurityLevel authNoPriv
defAuthPassphrase NetManage
defAuthType SHA

Adding this information means you won't have to enter your credentials everytime you use one of the SNMP utilities.

Configure SNMP on Your Router

For this exercise you need to work in groups. Assign one person to type on the keyboard.

If you are unsure of what group you are in refer to the Network Diagram on the classroom wiki by going to http://noc.ws.nsrc.org/ and clicking on the Network Diagram link.

Now connect to your router:

$ ssh cisco@rtrN.ws.nsrc.org    (or "ssh cisco@10.10.N.254")

username: cisco
password: <CLASS PASSWORD>

rtrN> enable
Password: <CLASS PASSWORD>
rtrN# configure terminal            (conf t)

Now we need to add an Access Control List rule for SNMP access, turn on SNMP, assign a read-only SNMP community string as well as a SNMPv3 group and user and tell the router to maintain SNMP information across reboots. To do this we do:

rtrN(config)# access-list 99 permit 10.10.0.0 0.0.255.255
rtrN(config)# snmp-server community NetManage ro 99
rtrN(config)# snmp-server group ReadGroup v3 auth access 99
rtrN(config)# snmp-server user admin ReadGroup v3 auth sha NetManage
rtrN(config)# snmp-server ifindex persist

Now let's exit and save this new configuration to the routers permanent config.

rtrN(config)# exit
rtrN# write memory                  (wr mem)
rtrN# exit                      (until you return to your pc)

Now to see if your changes are working.

Testing SNMP

To check that your SNMP installation works, run the snmpstatus command on each of the following devices

$ snmpstatus <IP_ADDRESS>

Where <IP_ADDRESS> is each of the following:

* The NOC server:       10.10.0.250
* Your group's router:  10.10.N.254
* The backbone router:  10.10.0.254

Note that you just used SNMPv3. Not all devices that implement SNMP support v3. Try again, adding "-v2c" as a parameter. Notice that the command automatically uses the community string in the snmp.conf file instead of the v3 user credentials. Try "-v1".

What happens if you try using the wrong community string (i.e. change NetManage to something else) using the options "-v2c -c NetWrong"?

SNMP Walk and OIDs

Now, you are going to use the snmpwalk command, part of the SNMP toolkit, to list the tables associated with the OIDs listed below, on each piece of equipment you tried above:

.1.3.6.1.2.1.2.2.1.2
.1.3.6.1.2.1.31.1.1.1.18
.1.3.6.1.4.1.9.9.13.1
.1.3.6.1.2.1.25.2.3.1
.1.3.6.1.2.1.25.4.2.1

You will try this with two forms of the snmpwalk command:

$ snmpwalk <IP_ADDRESS> <OID>

and

$ snmpwalk -On <IP_ADDRESS> <OID>

... where OID is one of the OIDs listed above: .1.3.6...

...where IP_ADDRESS can be your group's router...

Note: the -On option turns on numerical output, i.e.: no translation of the OID <-> MIB object takes place.

For these OIDs:

Do all the devices answer ?
Do you notice anything important about the OID on the output ?

Configuration of snmpd on your PC

For this exercise your group needs to verify that the snmpd service is running and responding to queries for all machines in your group. First enable snmpd on your machine, then test if your machine is responding, then check each machine of your other group members.

Install the SNMP agent (daemon)

$ sudo apt-get install snmpd
$ sudo apt-get install libsnmp-dev

Because of an Ubuntu bug (https://bugs.launchpad.net/ubuntu/+source/net-snmp/+bug/1322431), the command to create SNMPv3 users is missing, so, until this is fixed, do the following:

$ cd /tmp/
$ wget http://noc.ws.nsrc.org/downloads/snmp/net-snmp-create-v3-user
$ chmod +x net-snmp-create-v3-user
$ sudo mv net-snmp-create-v3-user /usr/local/bin

If the net-snmp-create-v3-user script is not available on noc.ws.nsrc.org you can obtain it by doing:

$ wget https://gist.githubusercontent.com/rarylson/72d1414d6907a4548427/raw/d97aed8debf0a291a0457ec634a3be370bd16546/net-snmp-create-v3-user

Configuration.

We will make a backup of the distributed config, and then we will create our own:

$ cd /etc/snmp
$ sudo mv snmpd.conf snmpd.conf.dist
$ sudo editor snmpd.conf

Then, copy/paste the following:

#  Listen for connections on all interfaces (both IPv4 *and* IPv6)
agentAddress udp:161,udp6:[::1]:161

# Configure Read-Only community and restrict who can connect
rocommunity NetManage  10.10.0.0/16
rocommunity NetManage  127.0.0.1

# Information about this host
sysLocation    NSRC Network Management Workshop
sysContact     sysadm@pcX.ws.nsrc.org

# Which OSI layers are active in this host
# (Application + End-to-End layers)
sysServices    72

# Include proprietary dskTable MIB (in addition to hrStorageTable)
includeAllDisks  10%

Now save and exit from the editor.

Now we will add the same SNMPv3 user to your PC. We need to stop snmpd before adding the user, and restart it to read the above changes as well as the new user:

$ sudo service snmpd stop
$ sudo net-snmp-create-v3-user -a SHA -A NetManage admin
$ sudo service snmpd start

Check that snmpd is working:

$ snmpstatus localhost

What do you observe ?

Test your neighbors

Check now that you can run snmpstatus against your other group members servers:

$ snmpstatus pcN.ws.nsrc.org

For instance, in group 5, you should verify against:

* pc17.ws.nsrc.org
* pc18.ws.nsrc.org
* pc19.ws.nsrc.org
* pc20.ws.nsrc.org

Adding MIBs

Remember when you ran:

$ snmpwalk 10.10.X.254 .1.3.6.1.4.1.9.9.13.1

If you noticed, the SNMP client (snmpwalk) couldn't interpret all the OIDs coming back from the Agent:

SNMPv2-SMI::enterprises.9.9.13.1.3.1.2.1 = STRING: "chassis"
SNMPv2-SMI::enterprises.9.9.13.1.3.1.6.1 = INTEGER: 1

What is 9.9.13.1.3.1 ?

To be able to interpret this information, we need to download extra MIBs:

We will use the following MIBs (Don't download them yet!):

CISCO MIBS

ftp://ftp.cisco.com/pub/mibs/v2/CISCO-SMI.my
ftp://ftp.cisco.com/pub/mibs/v2/CISCO-ENVMON-MIB.my

To make it easier, we have a local mirror on http://noc.ws.nsrc.org/mibs/

Download them now as follows:

$ cd /usr/share/mibs
$ sudo mkdir cisco
$ cd cisco

$ sudo wget http://noc.ws.nsrc.org/downloads/mibs/CISCO-SMI.my
$ sudo wget http://noc.ws.nsrc.org/downloads/mibs/CISCO-ENVMON-MIB.my

Now we need to tell the snmp tools that we have the cisco MIBS it should load. So edit the file /etc/snmp/snmp.conf, and add the following two lines:

mibdirs +/usr/share/mibs/cisco
mibs +CISCO-ENVMON-MIB:CISCO-SMI

Save the file, quit.

Now, try again:

$ snmpwalk 10.10.X.254  .1.3.6.1.4.1.9.9.13.1

What do you notice ?

SNMPwalk - the rest of MIB-II

Try and run snmpwalk on any hosts (routers, switches, machines) you have not tried yet, in the 10.10.0.X network

Note the kind of information you can obtain.

$ snmpwalk 10.10.0.X ifDescr
$ snmpwalk 10.10.0.X ifAlias
$ snmpwalk 10.10.0.X ifTable | less
$ snmpwalk 10.10.0.X ifXTable | less
$ snmpwalk 10.10.0.X ifOperStatus
$ snmpwalk 10.10.0.X ifAdminStatus
$ snmpwalk 10.10.0.X if

(Remember that with less you press space for next page, b to go back to previous page, and q to quit)

Can you see what's different between ifTable and ifXTable?

What do you think might be the difference between ifOperStatus and ifAdminStatus? Can you imagine a scenario where this could be useful ?

More MIB-OID fun

Use SNMP to examine:

the running processes on your neighbor's server (hrSWRun)
the amount of free diskspace on your neighbor's server (hrStorage)
the interfaces on your neighbor's server (ifIndex, ifDescr)

Can you use short names to walk these OID tables ?

Experiment with the "snmptranslate" command, example:

$ snmptranslate .1.3.6.1.4.1.9.9.13.1

Try with various OIDs