Old bar providing port (4)
I believe the answer is:
oban
'port' is the definition.
(Oban is a Scottish port)
'old bar' is the wordplay.
'old' becomes 'o' (abbreviation).
'bar' becomes 'ban' (I've seen this in another clue).
'o'+'ban'='OBAN'
'providing' is the link.
(Other definitions for oban that I've seen before include "small Scottish port" , "Argyll town" , "Port in western Scotland" , "Scottish west coast fishing and ferry port" , "Northern port" .)