SNMP exercises, part I ====================== Note: many of the commands in this exercise do not have to be run as root, but it is safe to run them all as root. So it's simpler if you start a root shell and enter them all there. You can start a root shell like this: $ sudo bash 0. Installing client tools -------------------------- # apt-get install snmp # 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. This has already been done for you here. Now, edit the file /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) 1. 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 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: rtrN> enable 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 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 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. 2. Testing SNMP --------------- To check that your SNMP installation works, run the snmpstatus command on each of the following devices $ snmpstatus -c 'NetManage' -v2c Where is each of the following: * The NOC server: 10.10.0.250 * Your group's router: 10.10.N.254 * The backbone switch: 10.10.0.253 * The access points: 10.10.0.251, 10.10.0.252 What happens if you try using the wrong community string (i.e. change 'NetManage' to something else?) 3. 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 -c 'NetManage' -v2c and $ snmpwalk -On -c 'NetManage' -v2c ... 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: a) Do all the devices answer ? b) Do you notice anything important about the OID on the output ? 4. 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) # apt-get install snmpd * Configuration. We will make a backup of the distributed config, and then we will create our own: # cd /etc/snmp # mv snmpd.conf snmpd.conf.dist # editor snmpd.conf Then, copy/paste the following (do not include the `-- cut here --` lines) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- cut here ------------------------- # 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% -- cut here ------------------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Now save and exit from the editor. * Restart snmpd # service snmpd restart 5. Check that snmpd is working: ------------------------------- $ snmpstatus -c 'NetManage' -v2c localhost What do you observe ? 6. Test your neighbors ---------------------- Check now that you can run snmpstatus against your other group members servers: $ snmpstatus -c 'NetManage' -v2c 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 7. Adding MIBs -------------- Remember when you ran: $ snmpwalk -c 'NetManage' -v2c 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 . Download them now as follows: # apt-get install wget # cd /usr/share/mibs # mkdir cisco # cd cisco # wget http://noc.ws.nsrc.org/mibs/CISCO-ENVMON-MIB.my # wget http://noc.ws.nsrc.org/mibs/CISCO-SMI.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 -c 'NetManage' -v2c 10.10.X.254 .1.3.6.1.4.1.9.9.13.1 What do you notice ? 8. 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 -c 'NetManage' -v2c 10.10.0.X ifDescr $ snmpwalk -c 'NetManage' -v2c 10.10.0.X ifAlias $ snmpwalk -c 'NetManage' -v2c 10.10.0.X ifTable | less $ snmpwalk -c 'NetManage' -v2c 10.10.0.X ifXTable | less $ snmpwalk -c 'NetManage' -v2c 10.10.0.X ifOperStatus $ snmpwalk -c 'NetManage' -v2c 10.10.0.X ifAdminStatus $ snmpwalk -c 'NetManage' -v2c 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 ? 9. More MIB-OID fun -------------------- * Use SNMP to examine: a) the running processes on your neighbor's server (hrSWRun) b) the amount of free diskspace on your neighbor's server (hrStorage) c) 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