Thanks to James for sending us some packets. Unlike suggested earlier, this doesn't look like a DoS against Google, but more like a DoS against vulnerable gateways. The SNMP command is actually a "set" command using the default read-write community string "private".
more here...........https://isc.sans.edu/diary/Google+DNS+Server+IP+Address+Spoofed+for+SNMP+reflective+Attacks/18647
more here...........https://isc.sans.edu/diary/Google+DNS+Server+IP+Address+Spoofed+for+SNMP+reflective+Attacks/18647