Problem when reading some non-existent OIDs about python-snmp HOT 2 OPEN

Assuming you are not setting msgMaxSize to something other than the default, this actually seems like a bug in the implementation of the agent. If an agent generates a response that is larger than the limit specified in the request, it's supposed to return a tooBig error. In this case, since it's not doing it, the UDP packet, which may be up to 65535 bytes is getting truncated by the ethernet layer, which supports a maximum payload of 1500 bytes. Clearly netsnmp is more fault-tolerant in this way, and it's able to detect that this is a valid packet that's simply been truncated by the network, and so it downgrades use a getNext request, which you would expect to have a smaller payload.

I'm not sure precisely what it would take to enable this type of fault-tolerance. It would probably involve creating a subclass of ParseError to replace the "Incomplete value" error in the decode() function in ber.py. The SNMPv3Message and PDU classes would need to be updated to continue parsing after detecting this error, in order to read the message/request ID, if possible, so that the proper RequestHandle can be notified of the failure, and propagate the error to the caller of getBulk().

In the meantime, you will probably need to manually limit the number of values you request at once, so that the agent will not generate responses that are too large.

from python-snmp.

In general, ZTE vendor's equipment is quite unstable. It is hard to argue with this.

To check, I reduced max-repetitions to 2 (it was 10) and got a correct response (from wireshark's point of view).

But anyway I see that net-snmp makes an additional snmp-get request to explicitly get noSuchObject. And this idea seems quite good to me.

Maybe that practice should be adopted for python-snmp as well? Including within the getNext and getBulk methods, so that instead of repeating snmp-get-next or snmp-get-bulk requests within a timeout, perform a snmp-get request to determine if the requested OID exists?

from python-snmp.