Is it rude to ask someone what their ethnicity is?

I like this eastern Asian man, and we've been chatting. I'm just genuinely curious what his ethnicity is, Chinese, Korean, Japanese, etc

I really wish I could distinguish the differences between them but I can't.
Is it rude to ask someone what their ethnicity is?
Yes, it's rude for some reason
No it's not
Other?
Select gender and age to cast your vote:
Updates
+1 y
What if we're trying to see if we should date or not? Does that make it any more or less appropriate? Not that his answer will change my mind about him, I like him a lot.
Updates
+1 y
I asked him, this is what he said: "Why would I be offended? I'm proud of where I'm from."
Is it rude to ask someone what their ethnicity is?
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