[SNMP4J] SNMP4J agent - different behaviour with different clients

[Young, Alistair]

Hi,
 
I've just started working with SNMP4J (and SNMP in general), and have
been very impressed with how quickly the library has helped me to get
something up and running.  However, I could use a little help.
 
I've built a very simple agent based upon TestAgent, and I've tried it
with two separate clients: net-snmp's snmpget and the graphical browser
Mibble.  When I use net-snmp, I successfully retrieve the value I'm
looking for.  Mibble, however, times out.
 
With the help of a packet sniffer, and plenty of debug information, I've
uncovered the following...
 
net-snmp snmpget:

*	net-snmp issues a non-specific 'get', specifying no engine ID,
boot count or time
*	agent responds with 1.3.6.1.6.3.15.1.1.4.0 ('unknown engine ID')
- the report includes the correct engine ID, plus boot count and time
both set to zero
*	net-snmp issues a 'get' for the desired OID, with the correct
engine ID, plus boot count and time both set to zero
*	agent responds with 1.3.6.1.6.3.15.1.1.2.0 ('not in time
window') - the report includes the correct engine ID, plus correct boot
count and time
*	net-snmp issues a 'get' for the desired OID, with the correct
engine ID, plus correct boot count and time
*	agent responds with the requested information

Mibble:

*	Mibble issues a 'get' for the desired OID, with the incorrect
engine ID and some non-zero values for boot count and time
*	agent throws some exceptions (Mibble retries a number of times,
each time causing an exception)
*	the Mibble request times out

The exception (manually transcribed, so forgive any typos!) is:
 
java.lang.NullPointerException
    at org.snmp4j.mp.MPv3.prepareDataElements(MPv3.java:1103)
    at
org.snmp4j.MessageDispatcherImpl.dispatchMessage(MessageDispatcherImpl.j
ava:263)
    ...
 
I'm using SNMP v3 with an 'authNoPriv' user.  I'm building against
snmp4j-1.9.3d and snmp4j-agent-1.2.2.
 
I've also tried querying a net-snmp agent using both client tools.  With
net-snmp as the agent, both client tools get the value they're looking
for.
 
Can anybody help to explain what is going on?  Might I have
misconfigured by agent in some way?
 
Any help would be appreciated!
 
Thanks,
 
 
Alistair.


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