A PoweredBy customer asked this morning about preserving the original source IP address on forwarded traps. I went looking for documentation covering our existing support for the snmpTrapAddress varbind but came up empty. The following should be added to the admin guide:

When SNMP traps are forwarded through a proxy using SNMPv2c or SNMPv3, preserving the original source IP address is a challenge due to the lack of an agent-addr field in the TRAP-V2 PDU used in those protocol versions. RFC 3584 defines an optional varbind snmpTrapAddress (.1.3.6.1.6.3.18.1.3.0) which can be added to forwarded traps to convey the original source IP address.

To configure OpenNMS Horizon to honor snmpTrapAddress when present, set use-address-from-varbind="true" in the top-level element of ${OPENNMS_HOME}/etc/trapd-configuration.xml and restart OpenNMS Horizon.