The SNMP source interface uses the IP address of the configured interface loopback, virtual interface or management IP as the source IP address for SNMP trap and inform packets originated from the device.
The specified interface acts as the source interface for SNMP trap and inform the packets. SNMP trap host can be configured for SNMP version 1, version 2, and version 3 per instance. If the source interface is not specified, the source IP address is the IP address of the interface through which packet exits device. If the source interface is modified (changing IP address), then it is reflected in the trap packets. Configured source interface IP address is not cached because the corresponding IP address can be modified. While sending out the SNMP trap packets to find the source IP address to use, the system checks and picks up the source interface configured. If an interface with no IP address is configured as the source interface, SNMP trap packets have the egress interface IP as the source IP.
The Source interface configurations are stored in the running-config and can be viewed using command name show running-config.
device# show running-config snmp-server host 192.168.12.5 $9$U13Qs06hXODXilnToF/r9Q== source-interface loopback 1