SNMP Informs sent from snmpd do not work if firewall is enabled on the machine

In case of a v2 inform, the Inform message is sent by the agent
(net-snmp 5.6.1) and received by the receiver but the ACK sent by the
receiver does not reach the agent since it is blocked by the firewall.
This results in the agent sending the Inform message again (n times
depending on the number of retries configured) and so there are
duplicate Informs at the receiver.

In case of a v3 Inform, before sending the actual Inform message, the
agent tries to discover the engineId of the receiver. The response to
the discover is not received by the agent and so it is not be able to
send out the Inform message itself.

We are using 'iptables' as the firewall on the linux machine where the
agent is running. The problem is that the Inform response is always on
a different UDP port, so it is not possible to configure a specific
port to allow incoming traffic.

Is there any way to get around this problem; any configuration in
net-snmp or for that matter any configuration in iptables ?

-Datta.

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