dereferencing type-punned pointer will break strict-aliasing rules

I have a unsigned char pointer which contains a structure.Now I want to do the following

unsigned char buffer[24];

//code to fill the buffer with the relevant information.

int len = ntohs((record_t*)buffer->len);

where record_t structure contains a field called len. I am not able to do so and am getting the error.

error: request for member ‘len’ in something not a structure or union.

Then I tried:

int len = ntohs(((record_t*)buffer)->len);

so as to get the operator precedence right. That gave me:

warning: dereferencing type-punned pointer will break strict-aliasing rules.

then I declared

record_t *rec = null;

rec = (record_t*)

what am I doing wrong here?