Good morning, We have some SNMP devices that do not respond to queries where the number of OIDs is over a certain limit. That is, they do respond to queries with N OIDs in the request, but return no response to queries with N+1 and more OIDs.
We have originally discussed the issue on #net-snmp IRC channel, but since there was no definite conclusion, we are moving the discussion here on the mailing list. Let me summarize what we have already talked about on IRC. First, we walk a device to obtain a list of OIDs it supports: $ snmpwalk -v 2c -c public 192.168.1.1 > walk.txt Then, we query a number of OIDs from that walk in a single GET request: $ head -29 walk.txt | cut -d' ' -f1 | xargs snmpget -d -r 0 -v 2c -c public 192.168.1.1 This responds normally with a 650 byte packet from UDP containing values for 29 variables. However, if we replace "29" in the above command with "30", then there is no response: "Timeout: No Response from 192.168.1.1." The problem might have to do with the fact that devices might have a limit on the size of the message they can produce. However, in that case we would expect the device to send a response with "tooBig" error code. Indeed, one of the devices we have does that: $ head -100 walk.txt | cut -d' ' -f1 | xargs snmpget -r 0 -v 1 -c public 192.168.1.2 Error in packet Reason: (tooBig) Response message would have been too large. Apparently, the device at 192.168.1.1 does not respond with "tooBig" and we wish to understand why. Is it a common behavior for devices and does it conform to some sort of specification? Maybe there is an object in one of the MIBs that controls it? For instance, it was suggested on IRC that SNMPv2-MIB::snmpSilentDrops might give a clue, but there is no such OID on this device, which is a respectable D-Link firewall: $ snmpget -v 2c -c public 192.168.1.1 SNMPv2-MIB::snmpSilentDrops SNMPv2-MIB::snmpSilentDrops = No Such Object available on this agent at this OID Another interesting observation is that using "snmpbulkget" can elicit a response with size much larger than the one "snmpget" fails at: $ head -29 walk.txt | cut -d' ' -f1 | xargs snmpbulkget -d -r 0 -v 2c -c public -Cn29 -Cr0 192.168.1.1 This works and we receive a response with 622 byte packet from UDP. Similar to "snmpget", replacing "29" with "30" gives no response. However, using "max-repetitions" instead of "non-repeaters" allows to get more values: $ head -1 walk.txt | cut -d' ' -f1 | xargs snmpbulkget -d -r 0 -v 2c -c public -Cn0 -Cr47 192.168.1.1 This works, too, and response of size 1020 bytes is received. Similarly, replacing "47" with "48" gives a timeout. If you could share your thoughts on the topic, that would be wonderful. Thank you, Aleksandrs ------------------------------------------------------------------------------ DreamFactory - Open Source REST & JSON Services for HTML5 & Native Apps OAuth, Users, Roles, SQL, NoSQL, BLOB Storage and External API Access Free app hosting. Or install the open source package on any LAMP server. Sign up and see examples for AngularJS, jQuery, Sencha Touch and Native! http://pubads.g.doubleclick.net/gampad/clk?id=63469471&iu=/4140/ostg.clktrk _______________________________________________ Net-snmp-users mailing list Net-snmp-users@lists.sourceforge.net Please see the following page to unsubscribe or change other options: https://lists.sourceforge.net/lists/listinfo/net-snmp-users
