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Re: I-D ACTION:draft-ietf-shim6-reach-detect-00.txt
Erik Nordmark wrote:
I see two potential reasons for not using any negative advice in the
1. If the probing by the shim (which is suppressible by positive
advice) have been designed so that a failure can be detected in N
seconds, then the shim would satisfy a requirement of detecting any
failure in, at worst, N seconds. Is it really useful to sometimes be
better, or is worst case the thing that matters? (I guess this is more
a question than a reason.)
Ok. (I wasn't so much arguing that we need to use negative advice, just
wondered why it couldn't be combined with this model.)
2. When you have multiple ULP "connections" using the same shim
context, you have some more complexity to handle when some ULP advice
might be negative and some positive at the same time (for the same
context). If you place more weight in the negative advice, then you
will react more strongly to random packet loss causing one connection
to think there is a problem, etc.
Only using positive advice avoids this complexity, because it
implicitly assumes that if anybody ULP finds the locator pair working,
then the probes can be suppressed.
This makes sense, but I worry that the argument
"one ULP works => others should work too" may not
hold in all cases. What if one ULP is TCP:xxxx->80, which
happens to work over this crappy firewalled network that
you are using, but it doesn't let through, say, TCP:xxxx->23?
The shim could be making the wrong decision here.