SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
The ALE supports OAM loopback on ports so that a remote link can be tested. That is a port placed in OAM loopback will echo packets received on a port back to the port with an egress op of 0xFF which will swap the SA and DA on egress in the CPSW.
Any supervisory packet will not be affected, so the spanning tree and other bridging functions are not affected.
Packets will only be echoed if the port is in OAM loopback mode, the received packet in not a supervisor packet. The port is in a forwarding state and the packet received DA!=SA and there are no errors in the packet.
When a port is in OAM loopback the port will not egress traffic from other ports, no address for loop backed traffic will be learned if enabled. Any packet received on the OAM loopback port with an error will be process as if the port is not in OAM. That is if the host has enabled copy errored frames the errored frames will be sent to the host instead.