The Gemara in Shabbos (111b-112a) establishes three categories of knots:
1) Prohibited by the Torah: ‘kesher hagamalin v’kesher hasapanim’ (lit. “the knot of the camel-drivers and sailors” - i.e. a tied loop that is permanently attached to the nose of the camel or the tip of the boat
2) Prohibited by the Rabbis: ‘kitra d’katri biz’mama uv’istrida’ (lit. “the knot that one ties onto the camel-loop or onto the boat-loop” – i.e. a non-permanent knot used to tie a longer rope onto the above-mentioned loops
3) Permissible: ‘kosheres isha mafteiach chalukah v’chulei’ (lit. “a woman may tie the strings of her garment, etc.”)
Two major interpretations are offered by the early-authorities (rishonim) as to how the above three categories are defined and differentiated. Note that according to the first interpretation, both permanence of the knot and the skill involved in making it, are factored in; whereas, according to the second interpretation, only the permanence factor is considered.
Summation: In contrasting the two interpretations, the following analysis emerges:
1) Rashi and Ro”sh rule more strictly than Rambam and Ri”f in that, according to Rashi and Ro”sh, a long-term knot is prohibited by the Rabbis, even if it is amateur, whereas according to Rambam and Ri”f, anything less than indefinitely permanent (and amateur) is permissible.
2) Rashi and Ro”sh rule more leniently than the Rambam and Ri”F in that, according to Rashi and Ro”sh, a short-term knot is permissible even if made professionally, whereas according to Rambam and Ri”f, any professional knot is prohibited, at least Rabbinically.