UP MEPs and Down MEPs have been aligned to better emulate service data. When an UP MEP or DOWN MEP is the source of the ETH-CFM PDU, the priority value configured, as part of the configuration of the MEP or specific test, is treated as the Forwarding Class (FC) by the egress QoS policy. The numerical ETH-CFM priority value resolves FCs using the following mapping:
0 — be
1 — l2
2 — af
3 — l1
4 — h2
5 — ef
6 — h1
7 — nc
If there is no egress QoS policy, the priority value is mapped to the CoS values in the frame. An ETH-CFM frame utilizing VLAN tags has the DEI bit mark the frame as ‟discard ineligible”. However, egress QoS Policy may overwrite this original value. The Service Assurance Agent (SAA) uses [fc {fc-name} [profile {in | out}]] to accomplish similar functionality.
UP MEPs and DOWN MEPs terminating an ETH-CFM PDU use the received FC as the return priority for the appropriate response, again feeding into the egress QoS policy as the FC.
This does not include Ethernet Linktrace Response (ETH-LTR). The specification requires the highest priority on the bridge port should be used in response to an Ethernet Linktrace Message (ETH-LTM). This provides the highest possible chance of the response returning to the source. Operators may configure the linktrace response priority of the MEP using the ccm-ltm-priority. MIPs inherit the MEPs priority unless the mip-ltr-priority is configured under the bridging instance for the association (config>eth-cfm>domain>assoc>bridge).