i am entering Hanoi on the 6th December 2012 and leaving for Bangkok on the l4th December 2012. I will be returning to Hanoi on the 22nd December 2012 to catch a flight to London, Heathrow but will not actually leave the airport. Do i need a single or multiple entry visa?
Since you donnot leave the international zone at the airport for the second arrival in Vietnam to change your flight, you only need to apply for a single entry visa.
Wish you an enjoyable trip.