Ethernet loopback operational modes
Ethernet loopback can be configured in the following modes:
In VLAN-unaware mode, the Ethernet loopback configuration is at the interface level and all the frames received on the ports are looped back irrespective of any VLAN. The port does not need to be explicitly assigned as a member of any VLAN. In VLAN-aware mode, the ports must be a part of the associated VLAN and all the frames received on the ports that are associated with a specific VLAN are looped back. The VLANs to which the port is not associated with the loopback function will continue to process traffic normally, allowing non-disruptive loopback testing.
A classification of the traffic flow can also be configured in VLAN-aware and VLAN-unaware modes. The loopback can be configured as flow-aware by specifying the source MAC address and destination MAC address on the interface. In the flow-aware configuration, only the frames received with a specific source MAC address and destination MAC address are looped back. During the loopback, the source MAC address and destination MAC address of the packets are swapped.
Ethernet loopback-enabled ports can send the incoming frames back to the source in the flow-unaware mode also. If the source MAC address and destination MAC address are not specified, all the frames received on the port are looped back and the port does not distinguish between control and data traffic and Ethernet address types (unicast, multicast, or broadcast). This makes the flow-unaware mode disruptive because control traffic is also looped back and affects other services operating on this port. However, this mode is effective when the traffic source device is directly connected to the port .
Ethernet loopback can be configured in the following combinations: