The ICMP Router Advertisement message is a part of ICMP Internet Router Discovery Protocol (IRDP). ICMP Internet Router Discovery Protocol (IRDP) is defined in RFC 1256. ICMP Router Advertisement allows a Router to advertise its presence in its network segment. Routers send ICMP Router Advertisement messages periodically as multicast messages to IPv4 multicast link-local address 220.127.116.11. 18.104.22.168 is the link-local multicast address to which all systems on local network segment listen. Thus a computer inside a network can discover their default gateway by listening to ICMP Router Advertisement messages.
ICMP Router Advertisement message Type number is 9. Please click next link, if you are not sure what are Type and Code fields in ICMP header.