This read-write INTEGER flag controls whether the received frame check sequence is preserved as-is or regenerated when the WAN port retransmits a packet. An admin sets this depending on whether downstream equipment needs the original FCS preserved for its own validation, or whether the device should recompute it after modifying the frame. Setting swanPreserveFCS to false(2) ensures the FCS is properly regenerated whenever the device alters a frame before retransmitting it on this WAN port.