Router Solicitation

Router Solicitation

The Router Solicitation message is sent by IPv6 hosts to discover the presence of IPv6 routers on the link. A host sends a multicast Router Solicitation message to prompt IPv6 routers to respond immediately, rather than waiting for an unsolicited Router Advertisement message. While Router Advertisements are transmitted periodically a host may prompt an immediate Router Advertisement using a Router Solicitation such as when it boots or following a restart operation. Router Solicitation messages are part of the ICMPv6 set.

An RS is an ICMP packet with Type 133. If the host already has an IP address, the source address of RS message is the host address. If the host has no IP address, it uses the unspecified address 0:0:0:0:0:0:0:0 as the source address. The destination is the IPv6 multicast address of "all routers on this subnet" 
i.e. FF02 :: 2.

  • The Source Address field is set to either a link-local IPv6 address assigned to the sending interface or the IPv6 unspecified address (::).
  • The Destination Address field is set to the link-local scope all-routers multicast address (FF02::2).

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