as the listening address in snmpd_input(..)
Stash the IPv4 address of the receiver via the recv(..) callback and use it in
the send(..) callback for the transport by specifying IP_SENDSRCADDR for the
control message type.
Add sendmsg logic to the UDP transport's send(..) callback and use the
respective send(..) callback for the transport instead of calling sendto in
snmpd_input(..).
MFC after: 3 weeks
Obtained from: Isilon OneFS (^/onefs/branches/BR_8_0_0_DEV@r507595)
Submitted by: Thor Steingrimsson <thor.steingrimsson@isilon.com>
Sponsored by: Dell EMC Isilon
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