[Bloat] [Babel-users] RTT stability inside a GRE tunnel

[Juliusz Chroboczek]

> 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.

The RTT is around 300 ms for both kinds of packets.  GRE packets have
virtually no jitter, while ICMP packets have some 15ms jitter, which
would appear to be completely random.

My guess would be that there might be a router in the way that handles
GRE packets in hardware, and ICMP packets in software.  The extra 15
ms is the CPU time spent on processing the ICMP packets.  Still, the
nondeterminacy is weird.

Anybody seen anything similar?

-- Juliusz