RE: Questions on draft-ietf-vrrp-ipv4-timers-02.txt

First, I just want to mention that I think Bob has the
answer to the "which time to use" question spot on. I
recall that the wording in the spec wasn't quite right
last time I read it (and it sounds like Bob agrees it
needs a little work), but the description Bob has here
in this e-mail agrees exactly with both my ponderings
and my experience on what can go wrong and what the
rules should be to make sure they don't.
 
But my purpose for writing this is to explore another
question, one that comes up over and over and I've
never felt satisfied about. Bob says, "As you move into lower 
time intervals between Advertisements, missing 3 Advertisements is very 
likely and flapping occurs." 
 
Now I *don't* have experience in actual networks where
these lower tolerances are required, so I ask this
without having an opinion, but is it in fact true that
that per packet failure rate increases in cases where
a shorter failover time is desired? What is the
characteristic of these environments that makes
the standard of 3 packets less reliable that in an
environment where a 3 second failover is acceptable?
It seems counter intuitive to me -- when you retransmit
faster, it causes a problem, and the solution to that
problem is to retransmit *even faster*? -- but, as I
say, it's probably just something about the target
application that I don't yet understand.
 
Or is this just because people have always wanted to
be able to configure the number of retransmissions, so
now's the chance? I admit to being a little concerned
with depending on only 3 retransmissions regardless of
the rate, but I've never actually been able to justify
any reason why three packets wouldn't be enough.
 
-don

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