IPv$6$ has been announced to be the next generation of IP addressing replacing IPv$4.$

a$)$ What$$s the main motivation of creating IPv$6$ for the replacement of IPv$4?$ Justify and elaborate on you answer. Please also provided the main reason why IPv$6$ usages adoption $7$is not as popular as it should be$.(6$ marks$)$

b$)$ IPv$6$ does not support fragmentation, describe in details how IPv$6$ is solving the maximum transfer unit $($MTU$)$ limitation$.$