If u traveling in the holy month of Ramadan u should have niyat for minimum 10days than u can take fast in ur traveling stay time in one city less than 10days u can’t take fast after Ramadan u can do qaza no need kaffarah just one fast against one fast, ham Allah ke hukm ke tabe hain jab who kahta hai roza rakho you rakhte hain jab woh kahta &ai safar main roza na rakho you nahi rakhte ibadat itaat ka naam han adat ka nahi