Christian, What is the purpose and what problems does this solve?  

I have a question be extension, why would we have the option to configure the mac address in the folloing example: interface GigabitEthernet0/0  mac-address 0201.aa00.0001  ipv6 address 2001:DB8:1111:1::/64 eui-64 -- R1# show ipv6 interface brief  Gi...