Hi,

While experimenting with the RTT-aware branch of babeld, I ran into an
odd but interesting behaviour: between two given hosts reachable over
the Internet, the RTT is more stable inside a GRE tunnel than outside.

I've measured the RTT between the two hosts (with a simple continuous
ping), both inside and outside the GRE tunnel.

The result is quite odd: the RTT has way more jitter inside the tunnel
(and is also somewhat lower) than outside.  See an excerpt of the data:

  http://ze.polyno.me/babel/ping-tunnel-oddity.png

I have absolutely no clue as to what could cause this behaviour; any
idea?

Baptiste