Case 3 --two global addresses and two default routers--

interface rtk0 down

(1)At first

Route of going and return decide at random. When going pass trough Power2, return can pass through Power3. Now, at first Dyna1 choose Power3 as the default router. Packet of "ping6" go trough Power3. And echo reply return trough Power3. Because, Dyna1 use 2001:200:0:8411:208:dff:fe76:f414 as the source address.

routing tables

Dyna1
Power1
Power2
Power3

ndp entry at Dyna1

Dyna1

(2)interface rtk0 down

Dyna1 changes the default router to Power2. And Dyna1 use 2001:200:0:8412:208:dff:fe76:f414. Because Dyna1 use 2001:200:0:8412:208:dff:fe76:f414 as the source address, ICMP echo reply go trough Power2 without OSPF.

routing tables

Dyna1
Power1
Power2
Power3

ndp entry at Dyna1

Dyna1