The following list contains important facts to consider when working with CFM loopbacks:
CFM loopbacks can be enabled on a per-port basis, and:
the port can be in access or network mode
once enabled on a port, all received LBM frames are processed, regardless of the VLAN and the service that the VLAN or SAP is bound to
there is no associated MEP creation involved with this feature; therefore, no domain, association, or similar checks are performed on the received frame
upon finding a destination address MAC match, the LBM frame is sent to the CFM process
CFM loopback support on a physical ring port on the 2-port 10GigE (Ethernet) Adapter card or 2-port 10GigE (Ethernet) module differs from other Ethernet ports. For these ports, cfm-loopback is configured, optionally, using dot1p and match-vlan to create a list of up to 16 VLANs. The null VLAN is always applied. The CFM Loopback Message will be processed if it does not contain a VLAN header, or if it contains a VLAN header with a VLAN ID that matches one in the configured match-vlan list.
received LBM frames undergo no queuing or scheduling in the ingress direction
at egress, loopback reply (LBR) frames are stored in their own queue; that is, a separate new queue is added exclusively for LBR frames
users can configure the way a response frame is treated among other user traffic stored in network queues; the configuration options are high-priority, low-priority, or dot1p, where dot1p applies only to physical ring ports
for network egress, where profiled scheduling is enabled, the following conditions apply:
high-priority: either cir = port_speed, which applies to all frames that are scheduled via an in-profile scheduler; or round-robin (RR) for all other (network egress queue) frames that are in-profile
low-priority: either cir = 0, pir = port_speed, which applies to all frames that are scheduled as out-of-profile, or RR for all other frames that are out-of-profile
for network egress or access egress, where 4-priority scheduling is enabled:
high-priority: either cir = port_speed, which applies to all frames that are scheduled via an expedited in-profile scheduler, or RR for all other (network egress queue) frames that reside in expedited queues and are in an in-profile state
low-priority: either cir = 0, pir = port_speed, which applies to all frames that are scheduled via a best effort out-of-profile scheduler, or RR for all other frames that reside in best-effort queues and are in an out-of-profile state
for the 8-port Gigabit Ethernet Adapter card, the 10-port 1GigE/1-port 10GigE X-Adapter card, and the v-port on the 2-port 10GigE (Ethernet) Adapter card and 2-port 10GigE (Ethernet) module, for network egress, where 16-priority scheduling is enabled:
high-priority: has higher priority than any user frames
low-priority: has lower priority than any user frames
for the physical ring ports on the 2-port 10GigE (Ethernet) Adapter card and 2-port 10GigE (Ethernet) module, which can only operate as network egress, the priority of the LBR frame is derived from the dot1p setting of the received LBM frame. Based on the assigned ring-type network queue policy, dot1p-to-queue mapping is handled using the same mapping rule that applies to all other user frames.
the above queue parameters and scheduler mappings are all preconfigured and cannot be altered. The desired QoS treatment is selected by enabling the CFM loopback and specifying high-priority, low-priority, or dot1p.