This question is very close to a previous question, Who were the Huns and/or Xiongnu?, but I hope it is clear that I'm not asking the same point.
In fact, I'm asking about the common assumption such as the one held by that earlier question, by asking explicitly:
Why do we believe (or on what basis make the assertion) that the Huns were the Xiongnu?
Example 1: On the earlier question, Who were the Huns and/or Xiongnu?, the question itself makes the assertion that they could be one and the same. But it was not explained why they could be (one and the same). Therefore, I am getting into the rationale, why OP or other readers are assuming the Huns and Xiongnu are related.
Example 2: This was an answer to the question which also made an assertion that the Xiongnu and Huns are related but, unfortunately, did not provide any historical documents/reasons, except referring to a blog/website that made an assertion.
If there are other information Iyou need me to provide for understanding thisclarify my question further, please statetell me in the comments but do say how this question is confusing or unclear.