Hello All,
I have a SNMP agent running on Linux OS, PowerPC Board.
SNMP agent is working fine, but recently came across this issue.
Problem:
SNMP agent is receiving duplicate Set/Get requests on its socket. These
Set/Get requests were duplicate of previously processed requests by the
agent.
General working of the Agent:
SNMP manager generates one SET request and then reads the five status
variables using GET request.
All the SET and GET requests have retries set to 0 and timeout value set
to 10 seconds.
All the SET and GET operations were successful.
This works fine, without any issue
Wireshark analysis shows the requests and corresponding responses from the
agent.
Problem trigger:
There is a FTP server implementation on the PPC board, and when manager
initiates a file upload to board,
There are duplicate SNMP responses observed on the Wireshark. These
responses match some of our previous successful set/get responses (request
ID match).
If we delay the FTP upload by 60 seconds from the successful SNMP set/get
requests, then this issue does not occur.
There are no request packets observed on the Wireshark, which confirms
that the requests are not duplicated by the manager. But when we debug the
SNMP agent,
SNMP main socket (select in snmpd.c receive()) receives the duplicate
requests.
Help:
I know this sounds very odd, and there may / may not be any direct
relation between FTP transfer and Duplicate responses. What I would like
to know is
Is there any mechanism in SNMP agent where it can resend the previous
requests to itself? or reprocess the requests?
I have debugged agent flow, and snmp_resend_request() function, but flow
never gets into this function in above case.
Any pointers, valuable debugging inputs from your experience will be of
great help
I am running very old version (net-snmp 5.1.1). Project is running for
almost 4 years now, there are lot of modifications gone in, and upgrading
to latest version is not possible at present.
Thanks and Regards,
Naveen
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