In at least v5.3.0.1 of Net-SNMP:
It appears that the net-snmp code is not RFC compliant with respect to
handling of msgMaxSize in SNMPv3 when the response is greater than the
msgMaxSize specified in the request ... As may occur with get bulk requests.
Specifically, if a request with a msgMaxSize specified as 2048 and the
response will be greater than 2048, the error message "Too long" is emitted
and no response is sent. This is not compliant to RFC 3416, which states in
section 4.2.3:
---- begin of rfc 3416 extraction ----
While the maximum number of variable bindings in the Response-PDU is
bounded by N + (M * R), the response may be generated with a lesser
number of variable bindings (possibly zero) for either of three
reasons.
(1) If the size of the message encapsulating the Response-PDU
containing the requested number of variable bindings would be
greater than either a local constraint or the maximum message
size of the originator, then the response is generated with a
lesser number of variable bindings. This lesser number is the
ordered set of variable bindings with some of the variable
bindings at the end of the set removed, such that the size of
the message encapsulating the Response-PDU is approximately
equal to but no greater than either a local constraint or the
maximum message size of the originator. Note that the number
of variable bindings removed has no relationship to the values
of N, M, or R.
---- end of rfc 3416 extraction ----
This implies that in the case of the response size being greater than the
msgMaxSize specified in the request that the response shall be "truncated"
to allow sending a response that does not expect the msgMaxSize.
Further, in error is the incorrect increment of SNMPv2-MIB counters. When a
msgMaxSize is specified in a request that would generate a response greater
than the msgMaxSize, as noted above, the response is incorrectly not sent,
but also in this case; snmpOutPkts is incremented and snmpSilentDrops is not
incremented.
--
Darren Besler
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