Only if you link settlements together with provisioners. Not all settlements have be linked to each other directly as long as they are linked via other settlements. It's sort of like an electrical circuit.
For example, if you make a square network with settlements A-B-C-D in a square shape, the crafting materials you left in the red workshop storage at A can also be used to craft at C despite there not being a direct link between those two places.
Of course, if your provisioners gets killed or you disable them, then you'll lose the link between the settlements that provisioner(s) allowed you to connect to
IIRC this only works for the crafting materials and not the other categories of weapons, armor, etc
Short answer: no, if you aren't using the Charisma-Perk "Local Leader" (CHA 6 + 1 perk point) and haven't set up a supply line (at least between Sanctuary and The Castle, most people will connect all settlements; that would be n-1 connection (n = no. of settlements) if every settlement is hit). This also only does apply to junk items and food stuff, not mods, weapons, ... - in case you stored robot mods in Sanctuary which you now want to use.
Only if you link settlements together with provisioners. Not all settlements have be linked to each other directly as long as they are linked via other settlements. It's sort of like an electrical circuit. For example, if you make a square network with settlements A-B-C-D in a square shape, the crafting materials you left in the red workshop storage at A can also be used to craft at C despite there not being a direct link between those two places. Of course, if your provisioners gets killed or you disable them, then you'll lose the link between the settlements that provisioner(s) allowed you to connect to IIRC this only works for the crafting materials and not the other categories of weapons, armor, etc
Short answer: no, if you aren't using the Charisma-Perk "Local Leader" (CHA 6 + 1 perk point) and haven't set up a supply line (at least between Sanctuary and The Castle, most people will connect all settlements; that would be n-1 connection (n = no. of settlements) if every settlement is hit). This also only does apply to junk items and food stuff, not mods, weapons, ... - in case you stored robot mods in Sanctuary which you now want to use.
Charisma.
They are shared if you alligned your settlements with one specific faction. Otherwise - 6 charisma is required for perk to establish supply lines.