[SNMP4J] ASN.1 data length error

[Frank Fock]

Hello Alistair,

For SNMP BER (which is not ASN.1 BER!), length > 4 bytes
are not allowed and do not make sense as the maximum length
of a SNMP packet is 65536 bytes.

Thus, the request is invalid. SNMP4J would be able to handle
it but ensures that the protocol is not violated (fail fast
strategy).

Best regards,
Frank

Young, Alistair wrote:
> Hello,
>  
> I have an agent built upon SNMP4J.  A third-party application is
> performing a number of gets and sets on the agent.  It all mostly works
> - however, I sometimes see the following error being logged:
>  
> ASN.1 parse error: Data length > 4 bytes are not supported!
>  
> I /think/ that this is in response to a 'set' request.
>  
> I found an old message on this subject, from this list's archives:
> http://lists.agentpp.org/pipermail/snmp4j/2007-May/002123.html
>  
> The response from Frank was "I would guess that the [...] tool does not
> correctly BER encode the request."
>  
> My knowledge of ASN.1 and BER is minimal (basically what I've gleaned
> from Wikipedia over the last 30 minutes!).  As I understand it, as well
> as specifying the length of a data value, it is also possible to specify
> the "length of the length".  This error suggests that whatever data is
> being received has a "length of the length" greater than 4 bytes.  As
> far as I can tell, this is valid ASN.1/BER.
>  
> So my question is - is this an invalid SNMP request (i.e. the 'client'
> application is wrong), or is this a limitation of SNMP4J (i.e. the agent
> application is wrong)?  Or possibly something else (is general
> corruption a possibility, or does the fact that the processing has got
> this far imply that the basic structure is sound?).
>  
> Many thanks for any help,
>  
>  
> Alistair.
> 
> 
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