Christian,

my only point was that using host probing does not allow you to see which link is down, since your traffic can go through different LOCs depending on the direction.

I agree in general with what you said, except that I do not think that probing in the network is harder than probing in the hosts, you just have a different viewpoint.

Luigi

Christian Vogt wrote:
Luigi Iannone wrote:

symmetric traffic : is the same remark as Dino, i.e., unidirectional
traffic.

symmetric routing: your data packet and your ack do not pass necessarily
through the same LOCs (which limits the capacity of discover the broken
link). Am I wrong?

Luigi and Dino:

The problem of asymmetric routing exists independently of whether you
probe explicitly, or implicitly using payload traffic.  Also, probing in
hosts (rather than in the network) does not make the problem harder.  In
fact, the problem gets harder if you probe in the network, because only
then do you potentially have to synchronize state over multiple boxes.

Regarding unidirectional traffic:  Yes, this requires explicit probing
into the silent direction.  And for host-based solutions, explicit
probing cannot easily be aggregated.  Having said this, I wouldn't take
it for granted that aggregation of probing traffic in network-based
solutions will in all situation yield a noticeable reduction in probing
traffic either.  The number of sessions between a given pair of networks
may be very small.

- Christian


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