Dropper posts have either internally (the most common) or externally routed cables. Whilst internal cabled droppers are the neatest and the most common (the cable emerges from the end of the post and runs through your frame to the bars) there aren’t actually that many frames that are designed to accommodate the extra cable, i.e. have a cable port near the head tube and a smooth enough transition round the bottom bracket. It is possible to make use of any existing cable ports, for instance if you run 1x shifting and have compatibility for x2, but it isn’t recommended by manufacturers as it is difficult to get round the BB. Alternative ways round this are to fit an externally routed dropper or go for one that uses wireless electronic technology.
Thanks to Hotlines for providing the cable port covers so we could fit all these droppers to a Rondo Ruut.