Is UCD_MSG_FLAG_EXPECT_RESPONSE must for traps ?

[niyas mydeen]

Hi Coders,

We use standard linux-3.10 kernel and net-snmp version 5.7.2 on powerpc
target.

As per RFC-2741, that now RESPONSE-PDU is generated for trap notify &
close in AgentX.
Is there any specific reason for that to get included? Because I see that
the flag UCD_MSG_FLAG_EXPECT_RESPONSE being set (in function
_agentx_realloc_build) for notify and these packets are getting saved in
queue for later retransmission. So it leads duplication trap at sometime.

Below is the tcpdump of the same issue:

21009 2017-04-14 09:22:18.334216 127.0.0.1 127.0.0.1 AgentX
366 Notify-PDU: sid=6, tid=0,* packid=679843704*, plen=292 >>>>OK
Trap

21011 2017-04-14 09:22:18.346861 127.0.0.1 127.0.0.1 AgentX
374 Response-PDU: sid=6, tid=0, packid=679843704, plen=300

21013 2017-04-14 09:22:18.518079 127.0.0.1 127.0.0.1 AgentX
74 Ping-PDU: sid=40, tid=0, packid=2102434099, plen=0

21014 2017-04-14 09:22:18.519092 127.0.0.1 127.0.0.1 AgentX
82 Response-PDU: sid=40, tid=0, packid=2102434099, plen=8

21019 2017-04-14 09:22:18.930801 127.0.0.1 127.0.0.1 AgentX
254 Notify-PDU: sid=12, tid=0, packid=1192, plen=180

21020 2017-04-14 09:22:18.967669 127.0.0.1 127.0.0.1 AgentX
154 Notify-PDU: sid=26, tid=0, packid=924, plen=80

21023 2017-04-14 09:22:19.004928 127.0.0.1 127.0.0.1 AgentX
154 Notify-PDU: sid=26, tid=0, packid=925, plen=80

21025 2017-04-14 09:22:19.021387 127.0.0.1 127.0.0.1 AgentX
262 Response-PDU: sid=12, tid=0, packid=1192, plen=188

21027 2017-04-14 09:22:19.099249 127.0.0.1 127.0.0.1 AgentX
162 Response-PDU: sid=26, tid=0, packid=924, plen=88

21029 2017-04-14 09:22:19.112175 127.0.0.1 127.0.0.1 AgentX
162 Response-PDU: sid=26, tid=0, packid=925, plen=88

21031 2017-04-14 09:22:20.470909 127.0.0.1 127.0.0.1 AgentX
366 Notify-PDU: sid=6, tid=0, *packid=679843704*, plen=292 >>>>OK
Trap

21032 2017-04-14 09:22:20.478677 127.0.0.1 127.0.0.1 AgentX
374 Response-PDU: sid=6, tid=0, packid=679843704, plen=300


And as per RFC-2471
"


*Note that the master agent's successful response indicates the
agentx-Notify-PDU was received and validated. It does not indicate
that any particular notifications were actually generated or received
by notification targets."*

So I tried disabling the flag for trap notify with the below patch and I
don’t see any such duplication of trap further on.

Is it oK to go with below snip ? OR Is there anyother way by which I can
stop the duplication of trap ?

--- a/agent/mibgroup/agentx/protocol.c
+++ b/agent/mibgroup/agentx/protocol.c
@@ -720,6 +720,11 @@ _agentx_realloc_build(u_char ** buf, size_t * buf_len,
size_t * out_len,

pdu->flags |= UCD_MSG_FLAG_EXPECT_RESPONSE;

+ /* double trap */
+ if(pdu->command == AGENTX_MSG_NOTIFY) {
+ pdu->flags &= ~UCD_MSG_FLAG_EXPECT_RESPONSE;
+ }
+
DEBUGDUMPHEADER("send", "AgentX Payload");
switch (pdu->command) {

diff --git a/snmplib/snmp_api.c b/snmplib/snmp_api.c
index 87c45a7..e3098f6 100644
--- a/snmplib/snmp_api.c
+++ b/snmplib/snmp_api.c
@@ -4804,6 +4804,7 @@ _sess_async_send(void *sessp,
case SNMP_MSG_REPORT:
case AGENTX_MSG_CLEANUPSET:
case AGENTX_MSG_RESPONSE:
+ case AGENTX_MSG_NOTIFY: /* SMX/CMX */

Thanks in Advance,
A. Mydeen.