TCP/IP Tutorial and Technical Overview - IBM Redbooks

Each router that receives the solicitation message responds with a router
advertisement sent directly to the node that sent the solicitation (not to the all
systems link-local multicast address).
Redirection
The router advertisement mechanism ensures that a node will always be aware
of one or more routers through which it is able to connect to devices outside of its
local links. However, in a situation where a node is aware of more than one
router, it is likely that the default router selected when sending data will not
always be the most suitable router to select for every packet. In this case,
ICMPv6 allows for redirection to a more efficient path for a particular destination.
Router A
Figure 9-20 Redirection example
Router B
Node
X
Consider the simple example shown in Figure 9-20. Node X is aware of routers A
and B, having received router advertisement messages from both. Node X wants
to send data to node Y. By comparing node Y's IP address against the local link
prefix, node X knows that node Y is not on the local link and that it must therefore
use a router. Node X selects router A from its list of default routers and forwards
the packet. Obviously, this is not the most efficient path to node Y. As soon as
Node
Y
Chapter 9. IP version 6 361