This is a tutorial with examples on how to use 'Net-snmp' on Linux to query network devices.
Figuring out all this was a time consuming and frustrating experience.
As with a lot of things, it all seems obvious once you know how it works.
I hope this will simplify getting to know the important commands for you.
Another good tutorial is here.
I used the MIB for the 'BreezeCOM DS.11 point-to-point Wireless Link' in these examples.
First, I had to correct problems with time-stamps in the MIB file, after getting these errors:
Bad month in timestamp (0000030000Z): At line 24 in /usr/share/snmp/mibs/DS11INTEG-MIB.txt
Bad month in timestamp (0000030000Z): At line 118 in /usr/share/snmp/mibs/DS11INTEG-MIB.txt
Bad month in timestamp (9900030000Z): At line 1217 in /usr/share/snmp/mibs/DS11INTEG-MIB.txt
To fix the error in line 24, I changed:
LAST-UPDATED "0000030000Z"
To:
LAST-UPDATED "0001030000Z"
presumably the format is 'yymmddhhmm'.
Also, I had this problem:
# snmpget -v1 -c public 192.168.49.253 dot11FCSErrorCount.1
IEEE802dot11-MIB::dot11FCSErrorCount.1 = Wrong Type (should be Counter32): INTEGER: 831199
# snmptranslate -Td IEEE802dot11-MIB::dot11FCSErrorCount
IEEE802dot11-MIB::dot11FCSErrorCount
dot11FCSErrorCount OBJECT-TYPE
-- FROM IEEE802dot11-MIB
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "This counter shall increment when an FCS error is
detected in a received MPDU."
So I edited the mib and changed 'Counter32' to 'Integer32', which seemed to fix it:
# snmpget -v1 -c public 192.168.49.253 dot11FCSErrorCount.1
IEEE802dot11-MIB::dot11FCSErrorCount.1 = INTEGER: 831202
When I have more time, I will read this.
### Using textual object identifiers ###
Adding a new mib file is NOT as simple as just copying it into '/usr/share/snmp/mibs/'
'snmpget' does not automatically load all the mibs in from that directory.
If the correct mib is not loaded, you get errors like "Unknown Object Identifier".
The name of the file containing the mib is NOT important or relavent.
You need to look in the file for the DEFINITIONS lines, and get the word
immediately before it. This is then the name of the mib 'Module'.
For example:
# cat /usr/share/snmp/mibs/DS11INTEG-MIB.txt | grep DEFINITIONS | awk '{print $1}'
BREEZECOM-GLOBAL-REG
BREEZECOM-DOT11EXT-MIB
BREEZECOM-SNMPGEN-MIB
IEEE802dot11-MIB
You then need to force the reading of all mibs like this:
# export MIBS=ALL
Or, alternatively, create '/usr/share/snmp/snmp.conf' and add this line:
mibfile /usr/share/snmp/mibs/DS11INTEG-MIB.txt
Then use the module name as follows:
# snmpget -v1 -c public 192.168.49.253 BREEZECOM-DOT11EXT-MIB::roamQuality.1
BREEZECOM-DOT11EXT-MIB::roamQuality.1 = INTEGER: 3
This should also then work:
# snmpget -v1 -c public 192.168.49.253 roamQuality.1
BREEZECOM-DOT11EXT-MIB::roamQuality.1 = INTEGER: 3
Use 'snmptranslate' to get the OID:
# snmptranslate -On BREEZECOM-DOT11EXT-MIB::roamQuality
.1.3.6.1.4.1.710.7.1.5.1.23.1.7
You can find the module for a given object, using a random access lookup:
# snmptranslate -IR roamQuality
BREEZECOM-DOT11EXT-MIB::roamQuality
Combining the previous two examples:
# snmptranslate -IR -On roamQuality
.1.3.6.1.4.1.710.7.1.5.1.23.1.7
To convert from numeric to textual, use this:
# snmptranslate .1.2.840.10036.2.2.1.12
IEEE802dot11-MIB::dot11FCSErrorCount
# snmptranslate -Of .1.2.840.10036.2.2.1.12
.iso.member-body.us.ieee802dot11.dot11mac.dot11CountersTable.dot11CountersEntry.dot11FCSErrorCount
To get full details from the mib, on an object:
# snmptranslate -Td BREEZECOM-DOT11EXT-MIB:roamQuality
BREEZECOM-DOT11EXT-MIB::roamQuality
roamQuality OBJECT-TYPE
-- FROM BREEZECOM-DOT11EXT-MIB
SYNTAX Integer32
MAX-ACCESS read-only
STATUS current
DESCRIPTION "An indicator for the quality of the BSS. The quality is
calculated over the received Beacons of the BSS and depends
on the selected quality indicator. The semantics of the
indicator is 'low is good quality' and 'high is bad quality'."
::= { iso(1) org(3) dod(6) internet(1) private(4) enterprises(1) breezeCOM(710) ds11Products(7) dot11ExtMIB(1) dot11ExtWBUObjs(5) roam(1) roamTable(23) roamEntry(1) 7 }
Another usefuls command is 'snmpwalk':
# snmpwalk -v1 -c public 192.168.49.253 dot11CountersTable
IEEE802dot11-MIB::dot11TransmittedFragmentCount.1 = INTEGER: 122172497
IEEE802dot11-MIB::dot11MulticastTransmittedFrameCount.1 = INTEGER: 45242
IEEE802dot11-MIB::dot11FailedCount.1 = INTEGER: 4009
IEEE802dot11-MIB::dot11RetryCount.1 = INTEGER: 1601483
IEEE802dot11-MIB::dot11MultipleRetryCount.1 = INTEGER: 885859
IEEE802dot11-MIB::dot11FrameDuplicateCount.1 = INTEGER: 543281
IEEE802dot11-MIB::dot11RTSSuccessCount.1 = INTEGER: 0
IEEE802dot11-MIB::dot11RTSFailureCount.1 = INTEGER: 0
IEEE802dot11-MIB::dot11ACKFailureCount.1 = INTEGER: 3971754
IEEE802dot11-MIB::dot11ReceivedFragmentCount.1 = INTEGER: 108826417
IEEE802dot11-MIB::dot11MulticastReceivedFrameCount.1 = INTEGER: 31359
IEEE802dot11-MIB::dot11FCSErrorCount.1 = INTEGER: 831325
IEEE802dot11-MIB::dot11TransmittedFrameCount.1 = INTEGER: 122156588
IEEE802dot11-MIB::dot11WEPUndecryptableCount.1 = INTEGER: 0
Note when using 'snmpget', you may need to append a .0 or a .1 to the OID, or you may get this problem:
# snmpget -v1 -c public 192.168.49.253 dot11ACKfailureCount
Error in packet
Reason: (noSuchName) There is no such variable name in this MIB.
Failed object: IEEE802dot11-MIB::dot11ACKFailureCount
# snmpget -v1 -c public 192.168.49.253 dot11ACKFailureCount.1
IEEE802dot11-MIB::dot11ACKFailureCount.1 = INTEGER: 3971912
Also note that the textual form is 'Case-Sensitive', as expected on a unix type system.
So if you use 'failure' instead of 'Failure', it fails!
# snmpget -v1 -c public 192.168.49.253 dot11ACKfailureCount.1
dot11ACKfailureCount.1: Unknown Object Identifier (Sub-id not found: (top) -> dot11ACKfailureCount)
Note, these examples were done with the following system configuration:
# rpm -qa | grep nmp
net-snmp-5.0.6-8.80.2
net-snmp-utils-5.0.6-8.80.2
# cat /etc/redhat-release
Red Hat Linux release 8.0 (Psyche)
Nigel Smith
2004-10-01
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