Ebay tracking number?

I bought an item on ebay,and I haven't received a tracking number in the details of the purchased item.Only when I asked the seller for the tracking number, he gave it to me, but I wasn't able to track the item on the site of his country's post nor on the site of my country. I wanted to ask if the tracking number is obligatory to be posted by the seller right after receiving the payment or he can choose to send it to the buyer only if the buyer requests it?It's only been 10 days since I've purchased the item, but it's starting to sound to me like a fraud...Should I be worried? Thanks