Cannot access Cisco MIBs via SNMPGET

Question

Hello, I'm sure this is a simple fix and I'm too stupid to figure it out, but I'm having trouble accessing Cisco ACE specific OIDs via Net-SNMPs tools. If I run snmpwalk on the device, I get a nice list of standard SNMP OIDs such as SNMPv2-MIB, IF-MIB, IP-MIB, etc with values such as the device name, interface IP counters and all that stuff. But I don't see any Cisco specific OIDs in the list. I really want to be able to monitor the load across real servers and server farms and such on this ACE module.
So, for example, I try running the following command and it says no such object:
snmpget -m +CISCO-SLB-MIB -On -v 2c -c communityname ipaddress CISCO-SLB-MIB::slbServerFarms
.1.3.6.1.4.1.9.9.161.1.2 = No Such Object available on this agent at this OID
I read you should try adding an index to the OID as there may be multiple sub objects (and of course there are multiple server farms) but I get the same thing:
snmpget -m +CISCO-SLB-MIB -On -v 2c -c communityname ipaddress CISCO-SLB-MIB::slbServerFarms.0
.1.3.6.1.4.1.9.9.161.1.2.0 = No Such Object available on this agent at this OID
Just to confirm a valid OID, I get this:
snmpget -m +CISCO-SLB-MIB -On -v 2c -c communityname ipaddress SNMPv2-MIB::sysDescr.0
.1.3.6.1.2.1.1.1.0 = STRING: Application Control Engine Service Module
I also tried snmptable with CISCO-ENHANCED-SLB-MIB::cesServerFarmRserverTable and it just says "Was that a table?"
So I think it must be a permission problem or some config that I have to tweak. Right now the only SNMP config is:
snmp-server community communityname group Network-Monitor
My device version info is:
Software
  loader:    Version 12.2[120]
  system:    Version A2(1.4) [build 3.0(0)A2(1.4) adbuild_11:54:12-2009/03/05_/auto/adbu-rel2/rel_a2_1_4_throttle/REL_3_0_0_A2_1_4]
  system image file: [LCP] disk0:c6ace-t1k9-mz.A2_1_4.bin
  installed license: ACE-SEC-LIC-K9 ACE-SSL-05K-K9
Thank you for your help!

Answer 1

This is an interesting thread, and probably something which is unclear to a lot of people.  Tables and their entries (think header rows) are inaccessible because they do not contain data directly.  Data is only contained in the cells within the table.  The cells in this case are the SNMP objects defined within each table entry (or row).  So, a table is inaccessible as a whole, but each of its data cells can be accessed.
If you think of it like a spreadsheet, it may be a little more useful.  But let's try a visual.
cesServerFarmRserverTable
cesServerFarmRserverPort
cesServerFarmRserverAdminWeight
cesServerFarmRserverOperWeight
80
100
100
8080
50
10
The header row in this table is called cesServerFarmRserverEntry.  It contains the column names for our data.  Each row has a unique number associated with it.  That is the cseServerFarmRserverPort.  In a typical spreadsheet program, this would be the column at the far left which you cannot edit.  It just enumerates the rows.  In this example, that column is named cesServerFarmRserverPort.  If I wanted to tell someone how to get the value of cesServerFarmRserverAdminWeight at a particular row, I would say, "go to row 80, and read the value from the cesServerFarmRserverAdminWeight column.  In this case, they would read 100.
SNMP operates in the same fashion.  For one to get a specific value (i.e. perform an SNMP GET), one must know the specific column name and row number.  In the actual case of the cesServerFarmRserverTable, the row number is actually a combination of the slbEntity, slbServerFarmName, cesRserverName, and cesServerFarmRserverPort, but the concept is the same.  You can only do an SNMP GET on a precise address in a given table (i.e. on a cell).  To do a GET on cesServerFarmRserverTable directly would make no sense since an atomic value could not be returned.
An SNMP Walk, on the other hand, allows you to start with the table itself, then walk through each cell in the table, printing out the value at that cell.
A tool like snmptable essentially performs recursive GET-NEXT queries to walk through all of the rows, then print the value of each cell in a tabular format.