ICMP Router advertisement/Router solicitation.
http://www.networksorcery.com/enp/protocol/icmp/msg9.htm
http://www.networksorcery.com/enp/protocol/icmp/msg10.htm
IP：BOOTP, RARP, or ICMP Address Mask messages
A host cannot process an advertisement until it has determined its own IP address(es) and subnet mask(s) for the interfaceon which the advertisement is received.On some links, a host may be able to use some combination of BOOTP, RARP, or ICMP Address Mask messages to discover itsown address and mask.While waiting to learn the address and mask of an interface, a host may save any valid advertisements received on that interfacefor later processing; this allows router discovery and address/mask discovery to proceed in parallel.