This reports the EtherType value the switch uses to identify and tag outgoing/incoming CFM frames (normally the standard IEEE 802.1ag EtherType), which is what lets the switch and its peers distinguish CFM control traffic from ordinary data frames on the wire. An admin checks this when CFM frames are unexpectedly being dropped or ignored by an intermediate device, since a mismatched or nonstandard EtherType configured here versus on a neighboring device would break CCM/CFM exchange even though both ends are otherwise correctly configured. For example, if a legacy piece of equipment in the path only recognizes the standard 0x8902 EtherType and cienaCesCfmEtherType has been changed away from that value, CFM frames would silently fail to be recognized end to end.