Is it possible that a neighbour could see my traffic (*), when we both have cable Internet? Or: Under which conditions might this be possible?
I would assume, "Never!", but after reading these two answers, I’m unsure.
At the Server Fault question ISP broadcasting all IP-packets, so I can see traffic of other clients from ISP, closetnoc answered:
For Cable, this is normal. Cable is segmented by neighborhoods depending upon area saturation. A neighborhood could be many miles or one block. This is normal since cable is not a frame connection but based upon broadcast standards much like ethernet over thin-net/thick-net back in the day. Your cable router may or may not enforce network segmentation depending upon the router, either by age or by model. Cable connections almost always see traffic on the WAN side that is not intended for the LAN. But sometimes WAN traffic can be seen on the LAN side. This is not unusual even today with the larger carriers.
In the "neighbour is the attacker" scenario, point-to-point mediums are also somewhat better than broadcast mediums; I know of some Cable providers where the cable is a thinly disguised carrier for ethernet frames, which are broadcasted throughout the building, the ISP "box" acting as a filter.
Am I misunderstanding something?
(* I’m not talking about a neighbour trying to sniff/decrypt my WLAN traffic, so assume that no WLAN is involved.)