what is the relation between internal and external fragmentation ?

Question

whenever we have internal fragmentation then we always have external fragmentation so but not vice-versa so is internal fragmentation a sufficient condition for external fragmentation , I guess it won't be a necessary condition since if there is no internal fragmentation then we can't say whether we have external fragmentation or not .

Answer 1

Here, It is not necessary that if there is internal fragmentation, then there is definitely external fragmentation. e.g Paging where there is no external fragmentation but there is chance to have internal fragmentation.
Also this can be conversely also true that if there is external fragmentation then it is not necessary that there will be internal fragmentation. Like in segmentation

Answer 2

You can take an example of the linked memory allocation method, where internal fragmentation exists but not external fragmentation. Because there all blocks are stored non-contiguously in the secondary memory, so using the link we can assign space for a newer file.