Chapter 13
| Basic Administration Protocols
Ethernet Ring Protection Switching
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If the switch goes into ring protection state due to a signal failure, after the
failure condition is cleared, the RPL owner will start the wait-to-restore timer
and wait until it expires to verify that the ring has stabilized before blocking the
RPL and returning to the Idle (normal operating) state.
◆ WTB Expire – The time before the wait-to-block timer expires.
◆ WTR Expire – The time before the wait-to-restore timer expires.
◆ West/East – Connects to next ring node to the west/east.
Each node must be connected to two neighbors on the ring. For convenience,
the ports connected are referred to as east and west ports. Alternatively, the
closest neighbor to the east should be the next node in the ring in a clockwise
direction, and the closest neighbor to the west should be the next node in the
ring in a counter-clockwise direction.
◆ Interface – The port or trunk attached to the west or east ring port.
Note that a ring port cannot be configured as a member of a spanning tree, a
dynamic trunk, or a static trunk.
◆ Port State – Once configured, this field shows the operational state of the ring
ports for this node:
■
Blocking – The transmission and reception of traffic is blocked and the
forwarding of R-APS messages is blocked, but the transmission of locally
generated R-APS messages is allowed and the reception of all R-APS
messages is allowed.
■
Forwarding – The transmission and reception of traffic is allowed;
transmission, reception and forwarding of R-APS messages is allowed.
■
Unknown – The interface is not in a known state.
◆ Local SF – Shows if a signal fault exists on a link to the local node.
◆ Local FS – Shows if a forced switch command was issued on this interface.
◆ Local MS – Shows if a manual switch command was issued on this interface.
◆ MEP – Specifies the CCM MEPs used to monitor the link on a ring node.
If a MEP is used to monitor the link status of an ERPS node with CFM continuity
check messages, then the MEG Level parameter on this configuration page
must match the authorized maintenance level of the CFM domain to which the
specified MEP belongs. (See “Configuring CFM Maintenance Domains” on
page 495.)
To ensure complete monitoring of a ring node, specify the CFM MEPs used to
monitor both the east and west ports of the ring node.
If CFM determines that a MEP node which has been configured to monitor a
ring port with this command has gone down, this information is passed to
ERPS, which in turn processes it as a ring node failure. For more information on
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