Having a hard time finding a definitive answer or method of testing. At a remote site, I have dual fiber connections bundled in an etherchannel/port-channel between my C6506 (upstream) and my C3750 (downstream). Lately I've noticed that one of the links heading towards the 3750 has been experiencing output drops. The C6506 isn't doing any type of L3 routing, but the method of load-balancing is "src-dst-ip", whereas the 3750 is "src-mac".
At first I though the C6506 might not be properly load-balancing at all, and simply forcing the traffic over one of the two link, since the citeria is "ip" based. That would explain the output drops. But, no. The counters were cleared 4 days ago and I see significant traffic over both links, so some type of balancing if happening.
My question is: From a L2 perspective, what's the best way of isolation the cause of the output drops?