[snmp] Problem with the snmpv3 context

[Birgit Arkesteijn]

On Mon, Mar 26, 2007 at 09:36:47AM +0100, Tim Panton wrote:
> 
> On 23 Mar 2007, at 21:16, Josh Bers wrote:
> 
> >I am seeing a problem while using version 5.1 of the stack (running 
> >on
> >linux, java 1.4.2_12) talking to an SNMP agent with version 3 with  
> >privacy
> >and authentication turned on.
> >
> >The scenario is the following:
> >
> >The program repeatedly attempts to contact an agent that is  
> >unreachable
> >(network cable unplugged). After a long period of time (>3 minutes)  
> >the
> >network cable is plugged back in.
> >
> >The stack behavior is:
> >
> >While disconnected, we see messages about USMDiscovery Bean timing 
> >out
> >trying to connect to the agent. The stack dump show 2 receivers  
> >associated
> >with the disconnected target IP address (?) These timeouts are  
> >repeated for
> >each attempt (timeouts take ~20 seconds). When the cable is  
> >reconnected, the
> >2 receiver threads suddenly die. No more USMDiscoveryBean timeouts  
> >are seen,
> >however, no every PDU that is sent times out waiting for a response  
> >(makes
> >sense given that the receiver has died).
> >
> >Anyone else seen this? Know why? Any workaround? Swapping to Version 
> >1
> >context solves the problem (but this is not desirable).
> >
> >Theory:
> >USMDiscovery Creates its own v3 context (not sure why it can't  
> >reuse the one
> >created for the original PDU??) Somehow when it kills this context  
> >it kills
> >the context (or at least the receiver thread) of the PDU's context...
> >(notify issue?)...
> 
> Ah, Interesting.
> 
> Do you have an ethereal trace of the packets - including ICMP ?
> Combined with a debug log we should be able to find the problem  
> pretty fast.
> (other pressures permitting :-) )
> 
> I dimly remember hearing that different UDP implementations throw  
> different
> exceptions when an intermediate router sends an 'unreachable' or the  
> local
> system reports 'no-route-to-host'. I'll ask the folks who reported  
> the problem what
> they did.
> 
> Tim.


Hi Josh,

To add to Tim's reply ..

See if you get anything useful when setting the debug level quite high 
( AsnObject.setDebug(13); )

As to why the v3 context cannot use the original PDU:
EngineId (and then Timeline) discovery requires different context
parameters.

Cheers, Birgit

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