The MPLS WG Archive

["David Allan" <dallan@nortelnetworks.com>]

Hi Curtis:

I think what you are proposing illustrates the complexity of the problem,
and highlights that we need a different approach in order for detecting
problems to be tractable. IMHO such constructs cannot be reliably and
proactively tested from a single arbitrary upstream point and what you
describe illustrates the complexity of actually performing meaningful
testing. This is compounded exponentially as load spreading points are
cascaded between the ingress and any point of failure.

IMHO the correct answer is to proactively test from more than one point in
the network and depend on the aggregate effect of the whole, and not try to
produce a protocol that reverse engineers proprietary boxes.

Each load spreading point should behave as a set of ingresses (from the POV
of probe injection) for some low frequency of probes. You live with not
necessaraily exercising all aspects of the actual load spreader but that is
true for any approach that is not ICMP monotonically going through the IP
address plan. 

This will provide bounded error detection in the network. Ideally you need
some smarts to locate the probe source closest to and upstream of the point
of failure once somthing goes wrong.  

food for thought
Dave