Speaking very much as an individual. I'm not objecting to echo nonces. However, I personally think we'll find they are not very useful. In particular, they are not useful in any of the following situations * square routing * triangle routing (a sends to b, c sends to a) * cannot detect a full path failure: in order to conclude you cannot reach someone you need to get packets from them I think that triangle and square routing will be very common unless we take active steps to avoid them. It seems likely that in any situation where you have multiple rlocs of the same priority you'll likely run into that case if you have a small number of flows. Long term, especially when we take security considerations into account, I think we'll end up with required control plane probing of locators with possible optimizations through the data plane. In that environment, I think echo nonces will serve no purpose. However this is just my opinion. I can't reason about or think about the performance implications until I understand the deployment model of LISP. In particular, the performance concerns that matter for probing on CPEs seem very different than say XTRs at an Amazon data center. Regardless of the above, I think getting data on echo nonces can do no harm.
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