I am configuring IPV6 in GNS3 lab environment for studying and when I configured the IP address, in Fa0/0 and S0/0 on both routers (R1 and R4) the Serial interface goes UP/UP for a few seconds and then it goes UP/Down and I am unable to ping the other side of the Serial Interface. I realized the S0/0 was obtaining the same Link Local IP than FA0/0; therefore, I manually change the link Local IP, but it did not help. Please, help me with this. Your help will be greatly appreciated. I tried the same configuration using IPV4 and everything works fine.
I just found the solution to this problem. It seems that in order for this configuration to work in GNS3, you have to first establish the serial link before creating all other links. Once you have successfully ping the other side of the WAN link, then you can start to configure all other links.