Historical field reports associated some switch configurations, including older Cisco Catalyst 4000 equipment, with DECnet or System Communications Services (SCS) packet loss under load.  Avanti 5.1.0 qualification did not reproduce the issue or qualify switch families, brands, speed classes, or prioritization behavior.

If packet loss is repeatable, preserve the failing topology and inspect switch counters, VLAN membership, filtering, loop protection, quality-of-service policy, and port negotiation before attributing it to unrecognized protocols.  Then try one controlled diagnostic at a time:

•Temporarily select a mutually supported fixed speed on the affected port and adapter, then repeat the same traffic test.

•Repeat the test through a known-good alternate switch or direct isolated path.

•Compare counters and packet traces from the failing and control paths.

Keep a changed speed or switch only when the controlled comparison corrects the recorded symptom.  Restore temporary settings otherwise.  Past success or failure with a brand or speed is not a current compatibility guarantee.