ICMP Router Solicitation
This event is triggered when a network host seeks to be configured with a default gateway, which usually occurs upon initialization of the hardware or if the existing default gateway is down.
The host sends a Router Solicitation (an ICMP message of Type 10, Code 0) to the all-routers multicast address (unless configured differently on your network) where all responding routers will reply with a Router Advertisement (Type 9, Code 0).