Chapter 13
| Basic Administration Protocols
Ethernet Ring Protection Switching
– 479 –
again. The major ring will not be broken, but the bandwidth of data traffic on
the major ring may suffer for a short period of time due to this flooding
behavior.
◆ Non-ERPS Device Protection – Sends non-standard health-check packets
when an owner node enters protection state without any link down event
having been detected through Signal Fault messages. (Default: Disabled)
■
The RPL owner node detects a failed link when it receives R-APS (SF - signal
fault) messages from nodes adjacent to the failed link. The owner then
enters protection state by unblocking the RPL. However, using this
standard recovery procedure may cause a non-EPRS device to become
isolated when the ERPS device adjacent to it detects a continuity check
message (CCM) loss event and blocks the link between the non-ERPS
device and ERPS device.
CCMs are propagated by the Connectivity Fault Management (CFM)
protocol as described under “Connectivity Fault Management” on
page 488. If the standard recovery procedure were used as shown in the
following figure, and node E detected CCM loss, it would send an R-APS (SF)
message to the RPL owner and block the link to node D, isolating that non-
ERPS device.
Figure 297: Non-ERPS Device Protection
When non-ERPS device protection is enabled on the ring, the ring ports on
the RPL owner node and non-owner nodes will not be blocked when signal
loss is detected by CCM loss events.
■
When non-ERPS device protection is enabled on an RPL owner node, it will
send non-standard health-check packets to poll the ring health when it
enters the protection state. It does not use the normal procedure of waiting
to receive an R-APS (NR - no request) message from nodes adjacent to the
recovered link. Instead, it waits to see if the non-standard health-check
packets loop back. If they do, indicating that the fault has been resolved,
the RPL will be blocked.
After blocking the RPL, the owner node will still transmit an R-APS (NR, RB -
ring blocked) message. ERPS-compliant nodes receiving this message flush
their forwarding database and unblock previously blocked ports. The ring
is now returned to Idle state.
◆ Holdoff Timer – The hold-off timer is used to filter out intermittent link faults.
Faults will only be reported to the ring protection mechanism if this timer
expires. (Range: 0-10000 milliseconds, in steps of 100 milliseconds)
non-ERPS
A
non-ERPS
RPL
Owner
RPL
XX
blocked blocked
fault
BCDEF
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