[Babel-users] RTT stability inside a GRE tunnel

[Michael Richardson]

Can you tell us a bit how about how you are measuring, and what the remote
side is?   I see that the two values are consistent with each other --- it
looks to me like the inside tunnel value is simply truncated.

I assume that you are measuring the RTT value from babeld, rather than from
the network itself (i.e. with tcpdump).

This is what I would *suspect*:

Coming out of the GRE tunnel, your packet would have to be decapsulated by
the kernel, and then re-queued into the network bottom half.  Generally,
the kernel does interrupt mitigation, and since this is a soft-interrupt,
that queue is serviced from a clock interrupt.

As such, you'd see the values quantized to the clock interrupt, which is
exactly what I see in your diagram.

--
]               Never tell me the odds!                 | ipv6 mesh networks [
]   Michael Richardson, Sandelman Software Works        | network architect  [
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