Interface Configuration Guide 7705 SAR Interfaces
Edition: 01 3HE 11011 AAAC TQZZA 89
An Ethernet port loopback may interact with other features. See Interaction of
Ethernet Port Loopback with Other Features for more information.
3.2.9.1.1 MAC Swapping
Typically, an Ethernet port loopback only echoes back received frames. That is, the
received source and destination MAC addresses are not swapped. However, not all
Ethernet equipment supports echo mode, where the original sender of the frame
must support receiving its own port MAC address as the destination MAC address.
The MAC swapping feature on the 7705 SAR is an optional feature that will swap the
received destination MAC address with the source MAC address when an Ethernet
port is in loopback mode. After the swap, the FCS is recalculated to ensure the
validity of the Ethernet frame and to ensure that the frame is not dropped by the
original sender due to a CRC error.
MAC swapping is not supported on the GPON module, 6-port DSL Combination
module, or 8-port xDSL module.
3.2.9.1.2 Interaction of Ethernet Port Loopback with Other Features
EFM OAM and line loopback are mutually exclusive. If one of these functions is
enabled, it must be disabled before the other can be used.
However, a line loopback precedes the dot1x behavior. That is, if the port is already
dot1x-authenticated it will remain so. If it is not, EAP authentication will fail.
Ethernet port-layer line loopback and Ethernet port-layer internal loopback can be
enabled on the same port with the down-when-looped feature. EFM OAM cannot be
enabled on the same port with the down-when-looped feature. For more information,
see Ethernet Port Down-When-Looped.
3.2.9.2 CFM Loopbacks for OAM on Ethernet Ports
This section contains information on the following topics:
• CFM Loopback Overview
• CFM Loopback Mechanics
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