Interface Configuration Guide 7705 SAR Interfaces
Edition: 01 3HE 11011 AAAC TQZZA 93
• 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.
3.2.10 Ethernet Port Down-When-Looped
Newly provisioned circuits are often put into loopback with a physical loopback cable
for testing and to ensure the ports meet the SLA. If loopbacks are not cleared, or
physically removed, by the operator when the testing is completed, they can
adversely affect the performance of all other SDPs and customer interfaces (SAPs).
This is especially problematic for point-to-multipoint services such as VPLS, since
Ethernet does not support TTL, which is essential in terminating loops.
The down-when-looped feature is used on the 7705 SAR to detect loops within the
network and to ensure continued operation of other ports. When the
down-when-looped feature is activated, a keepalive loop PDU is transmitted
periodically toward the network. The Ethernet port then listens for returning keepalive
loop PDUs. In unicast mode, a loop is detected if any of the received PDUs have an
Ethertype value of 9000, which indicates a loopback (Configuration Test Protocol),
and the source (SRC) and destination (DST) MAC addresses are identical to the
MAC address of the Ethernet port. In broadcast mode, a loop is detected if any of the
received PDUs have an Ethertype value of 9000 and the SRC MAC address matches
the MAC address of the Ethernet port and the DST MAC address matches the
broadcast MAC address. When a loop is detected, the Ethernet port is immediately
brought down. Down-when-looped is supported on Ethernet ports, DSL module
ports, and GPON module ports.
Ethernet port-layer line loopbacks and the down-when-looped feature can be
enabled on the same port. The keepalive loop PDU is still transmitted; however, if the
port receives its own keepalive loop PDU, the keepalive PDU is extracted and
processed to avoid infinite looping.
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