Start by installing the net-snmp tools on your individual host. Connect via ssh to hostX.campusY:
$ sudo apt install snmp
$ sudo apt install snmp-mibs-downloaderThe second of the two commands downloads the standard IETF and IANA SNMP MIBs which are not included by default.
Note: to find snmp-mibs-downloader, you must enable the “multiverse” source in your APT configuration. This has already been done for you in this workshop.
Now, edit the file /etc/snmp/snmp.conf:
$ sudo editor /etc/snmp/snmp.confChange 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).
Save this file and exit.
Now, in your home directory make a .snmp directory with file snmp.conf inside it, make it readable only by you, and add the credentials to it:
$ cd
$ mkdir .snmp
$ chmod 700 .snmp/
$ editor .snmp/snmp.confPut the following contents in the file:
defVersion 3
defSecurityLevel authNoPriv
defSecurityName admin
defAuthPassphrase NetManage
defAuthType SHA
defPrivType AES
# Default community when using SNMP v2c
defCommunity NetManageCreating this configuration file means you won’t have to enter your credentials everytime you use one of the SNMP utilities. Otherwise you would have to add all these values on the command line like this:
(this command will not yet work)
snmpstatus -v3 -l authNoPriv -a SHA -u admin -A NetManage hostX.campusYFor this exercise you need to work together as a group. You will be enabling and configuring snmp to run on each of your 4 campus network devices. This includes:
* bdr1.campusY
* core1.campusY
* dist1-b1.campusY
* dist1-b2.campusYThe commands to enable ssh are the same on each box, so divide the work between your group member:
Now connect to your campus network devices and on each do:
$ ssh nmmlab@DEVICE.campusY.ws.nsrc.org
username: nmmlab
password: <CLASS PASSWORD>
DEVICE.campusY> enable
Password: <CLASS PASSWORD>
DEVICE.campusY# 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:
(Note that “Y” is equal to your campus number)
DEVICE.campusY(config)# snmp-server community NetManage ro 99
DEVICE.campusY(config)# snmp-server group ReadGroup v3 auth access 99
DEVICE.campusY(config)# access-list 99 permit 100.68.Y.128 0.0.0.15
DEVICE.campusY(config)# access-list 99 permit 100.64.0.0 0.0.3.255
DEVICE.campusY(config)# snmp-server user admin ReadGroup v3 auth sha NetManage
DEVICE.campusY(config)# snmp-server ifindex persistNow let’s exit and save this new configuration to the routers permanent config.
DEVICE.campusY(config)# exit
DEVICE.campusY# write memory (wr mem)
DEVICE.campusY# exit (until you return to your pc)If you have questions about what the access-list statement is restricting ask your instructors.
To check that your SNMP installation works, run the snmpstatus command on each of the following devices from your host:
$ snmpstatus <IP_ADDRESS>Where
* Campus border router: 100.68.Y.1
* Campus core switch: 100.68.Y.2
* Building 1 distribution switch: 172.2Y.10.2
* Building 2 distribution switch: 172.2Y.20.2Note 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”. That is try:
$ snmpstatus -v2c <IP_ADDRESS>and
$ snmpstatus -v1 <IP_ADDRESS>What happens if you try using the wrong community string (i.e. change NetManage to something else) using the options “-v2c -c NetWrong”?
$ snmpstatus -v2c -c NetWrong <IP_ADDRESS>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
.1.3.6.1.4.1.9.9.92.1
.1.3.6.1.2.1.25.2.3.1
.1.3.6.1.2.1.25.4.2.1You will try this with two forms of the snmpwalk command:
$ snmpwalk -v2c <IP_ADDRESS> <OID>and
$ snmpwalk -v2c -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:
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.
$ sudo apt install snmpd
$ sudo apt install libsnmp-devWe will make a backup of the distributed config, and then we will create our own (be sure you mv “snmpd.conf” and not “snmp.conf”):
$ cd /etc/snmp
$ sudo mv snmpd.conf snmpd.conf.dist
$ sudo editor snmpd.confThen, copy/paste the following (change hostX.campusY to your own host and campus number) and replace “Y” with your campus number:
# Listen for connections on all interfaces (both IPv4 *and* IPv6)
agentAddress udp:161,udp6:161
# For SNMPv2: Configure Read-Only community and restrict who can connect
rocommunity NetManage 100.64.0.0/22
rocommunity NetManage 100.68.Y.128/28
rocommunity NetManage 127.0.0.1
rocommunity6 NetManage 2001:db8:Y:1::/64
rocommunity6 NetManage ::1
# Information about this host
sysLocation NSRC Network Management Workshop
sysContact sysadm@hostX.campusY.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 systemctl stop snmpd
$ sudo net-snmp-create-v3-user -X AES -a SHA -A NetManage admin
$ sudo systemctl start snmpd$ snmpstatus localhostWhat do you observe ?
Check now that you can run snmpstatus against your other group members host.
$ snmpstatus host[1..6].campusY.ws.nsrc.orgFor instance, in group 5, you should verify against:
* host1.campus5.ws.nsrc.org
* host2.campus5.ws.nsrc.org
* host3.campus5.ws.nsrc.org
* host4.campus5.ws.nsrc.org
* host5.campus5.ws.nsrc.org
* host6.campus5.ws.nsrc.organd, so on.
Be sure that you install the snmp daemon (agent) on your campus server at this time. Select someone from your group to do this. Otherwise, it will be configured later as well.
At a minimum you need to complete sections 3 and 7 to 7.1.
Remember when you ran:
$ snmpwalk 100.68.Y.1 .1.3.6.1.4.1.9.9.92.1If you noticed, the SNMP client (snmpwalk) couldn’t interpret all the OIDs coming back from the Agent:
SNMPv2-SMI::enterprises.9.9.92.1.1.1.1.1 = STRING: "Cisco"
SNMPv2-SMI::enterprises.9.9.92.1.1.1.2.1 = STRING: "92D8PBYYIWNV8D4765QH3"
SNMPv2-SMI::enterprises.9.9.92.1.1.1.3.1 = STRING: "IOSv"
SNMPv2-SMI::enterprises.9.9.92.1.1.1.4.1 = STRING: "1.0"What is 9.9.92.1.1.1.4.1 ?
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-ENTITY-ASSET-MIB.myTo make it easier, we have a local mirror on http://www.ws.nsrc.org/downloads/mibs/
Download them now as follows:
$ cd /usr/share/mibs
$ sudo mkdir cisco
$ cd cisco
$ sudo wget http://www.ws.nsrc.org/downloads/mibs/CISCO-SMI.my
$ sudo wget http://www.ws.nsrc.org/downloads/mibs/CISCO-ENTITY-ASSET-MIB.myNow 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 to the end of the file:
mibdirs +/usr/share/mibs/cisco
mibs +CISCO-SMI:CISCO-ENTITY-ASSET-MIBSave the file, quit.
Now, try again (the example uses bdr1.campusY.ws.nsrc.org below. You can do this whichever network device you are configuring):
$ snmpwalk 100.68.Y.1 .1.3.6.1.4.1.9.9.92.1What do you notice ?
Try and run snmpwalk on any hosts (routers, switches, machines) you have not tried yet, in the 100.68 address range.
Note the kind of information you can obtain.
(For your building distribution switches use 172.2Y.10.2 and 172.2Y.20.2)
$ snmpwalk 100.68.Y.1 ifDescr
$ snmpwalk 100.68.Y.1 ifAlias
$ snmpwalk 100.68.Y.1 ifTable | less
$ snmpwalk 100.68.Y.1 ifXTable | less
$ snmpwalk 100.68.Y.1 ifOperStatus
$ snmpwalk 100.68.Y.1 ifAdminStatus
$ snmpwalk 100.68.Y.1 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 ?
Can you use short names to walk these OID tables ?
$ snmptranslate .1.3.6.1.4.1.9.9.92.1You may notice in /var/log/syslog that snmpd logs a message for every single packet:
Jun 12 17:20:04 noc snmpd[3362]: Connection from UDP: [100.64.0.250]:49147->[100.64.0.250]:161
Jun 12 17:20:04 noc snmpd[3362]: Connection from UDP: [100.64.0.250]:49147->[100.64.0.250]:161
Jun 12 17:20:04 noc snmpd[3362]: Connection from UDP: [127.0.0.1]:56997->[127.0.0.1]:161
Jun 12 17:20:04 noc snmpd[3362]: Connection from UDP: [127.0.0.1]:56997->[127.0.0.1]:161This wastes disk space. You can make snmpd less chatty by starting it with different options, changing -Lsd to -LSwd
Note carefully the capitalization! See
LOGGING OPTIONSinman snmpcmdfor the meaning of these flags.
Find the existing options like this:
grep ExecStart= /lib/systemd/system/snmpd.serviceThen run systemctl edit snmpd.service, enter the following and save:
[Service]
ExecStart=
ExecStart=/usr/sbin/snmpd -LSwd -Lf /dev/null -u Debian-snmp -g Debian-snmp -I -smux,mteTrigger,mteTriggerConf -fThis creates /etc/systemd/system/snmpd.service.d/override.conf. Note that the extra blank ExecStart= line is required; this tells systemd that you are replacing the existing ExecStart line, not adding another one.
When you restart snmpd, it should now be running with the new flags.