Technique 1:
SORT it_likp BY vbeln.
SORT it_lips BY vbeln.
LOOP AT it_likp INTO wa_likp.
READ TABLE it_lips WITH KEY vbeln = wa_likp-vbeln TRANSPORTING NO FIELDS BINARY SEARCH.
IF sy-subrc = 0.
lv_indx = sy-tabix.
LOOP AT it_lips INTO wa_lips FROM lv_indx.
IF wa_lips-vbeln NE wa_likp-vbeln.
EXIT.
ENDIF.
counter = counter + 1.
ENDLOOP.
ENDIF.
ENDLOOP.
Technique 2:
SORT: it_likp BY vbeln,
it_lips BY vbeln.
lv_tabix = 1. " Set the starting index 1
CLEAR counter.
LOOP AT it_likp ASSIGNING <lfs_likp>.
" Start the nested LOOP from the index
LOOP AT it_lips FROM lv_tabix
ASSIGNING <lfs_lips>.
" Save index & Exit the loop, if the keys are not same
IF <lfs_likp>-vbeln <> <lfs_lips>-vbeln.
lv_tabix = sy-tabix.
EXIT.
ELSE.
" Rest of the logic would go from here...
" counter to check how many times the actual processing was made.
counter = counter + 1.
ENDIF.
ENDLOOP.
ENDLOOP.
Technique 2 will not work if the it_likp table doesn't contain the primary key of the it_lips table.
