Peder> The scotty, in the role of command generator, specifies a
Peder> maxSizeResponseScopedPDU (the value is 2048) in a request. My
Peder> implementation, as command responder, produces a response where
Peder> the ScopedPDU is less than 2048, but the entire message is
Peder> slightly larger (2070 bytes). Scotty complains:
Peder> msgLen 2048, msgSeqLen 2066, plus 4
Peder> Says the snmpv3 architecture document:
Peder> 3.4.1. maxSizeResponseScopedPDU
Peder> The maxSizeResponseScopedPDU is the maximum size of a scopedPDU
Peder> that a PDU's sender would be willing to accept. Note that the
Peder> size of a scopedPDU does not include the size of the SNMP
Peder> message header.
Peder> I think scotty 3 needs a minor fix here.
Do not confuse the maxSizeResponseScopedPDU parameter of the ASIs with
the msgMaxSize field in the message. RFC 2272 section 6.3 says:
: 6.3. msgMaxSize
:
: The msgMaxSize field of the message conveys the maximum message size
: supported by the sender of the message, i.e., the maximum message
: size that the sender can accept when another SNMP engine sends an
: SNMP message (be it a response or any other message) to the sender of
: this message.
:
: When an SNMP message is being generated, the msgMaxSize is provided
: by the SNMP engine which generates the message. At the receiving
: SNMP engine, the msgMaxSize is used to determine how big the Response
: to a Request message can be.
I think scotty is therefore right to put the msgMaxSize in the message
header. Its the responsibility of the receiving SNMP engine to
calculate the maxSizeResponseScopedPDU out of the msgMaxSize. You
basically need to calculate the max. size of the message header for a
given message processing model plus security model. You may also want
to look at the actual security level.
[I think it would be nice if the RFCs would contain precise hints on
how to derive maxSizeResponseScopedPDU from msgMaxSize. It might be
useful to bring this up on the SNMPv3 mailing list so that this can be
clarified in the next revision cycle.]
Juergen
-- Juergen Schoenwaelder schoenw@ibr.cs.tu-bs.de http://www.cs.tu-bs.de/~schoenw Technical University Braunschweig, Dept. Operating Systems & Computer Networks Bueltenweg 74/75, 38106 Braunschweig, Germany. (Tel. +49 531 / 391 3289)-- !! This message is brought to you via the `tkined & scotty' mailing list. !! Please do not reply to this message to unsubscribe. To subscribe or !! unsubscribe, send a mail message to <tkined-request@ibr.cs.tu-bs.de>. !! See http://wwwsnmp.cs.utwente.nl/~schoenw/scotty/ for more information.