OmniSwitch OS6860/OS6900/OS10K Troubleshooting Guide Part No.032996-00 Rev.A
AOS Release 7.X and 8.X January 2015
Alcatel-Lucent Page 130 of 148
20. Troubleshooting Ethernet Ring Protection
(ERP)
Ethernet Ring Protection (ERP) is a feature/algorithm that provides loop-free topology with redundancy and
scalbility. Loop prevention is carried out throughout the links, with one of the links blocked. Implementation
of ERP is based on the Recommendation ITU-T G.8032/Y.1344 standard.
ERP operates over standard Ethernet interfaces that are physically connected in a ring topology. In an Ethernet
ring, each node is connected to two adjacent nodes using two independent links called ring links. A ring link is
bound by two adjacent nodes on ports called ring ports. The ring nodes support standard FDB (Filtering
database) MAC learning, forwarding, flush behavior, and port blocking and unblocking mechanisms.
Any failure along the ring triggers a R-APS(SF) (R-APS signal fail) message along both directions from the
nodes adjacent to the failed link after these nodes have blocked the port facing the failed link. On obtaining
this message, RPL owner unblocks the RPL port.
During the recovery phase when the failed link gets restored the nodes adjacent to the restored link send R-
APS(NR) (R-APS no request) messages. On obtaining this message, the RPL owner block the RPL port and
then sends a R-APS(NR,RB) (R-APS no request, root blocked) message. This will cause all other nodes other
than RPL owner in the ring to unblock all the blocked ports.
A ring operates in one of two modes:
Idle mode is the normal operation when all links up and RPL is blocked and Protection mode occurs when
protection switching is activated. A ring failure will trigger the RPL into a forwarding state).
By default, Spanning Tree will not operate on the ERP ring ports. When the port remains an ERP port it will
not control the blocking/forwarding behavior of the port. Spanning Tree will be active on all other switch ports
and will determine the blocking or forwarding state of VLANs configured on those ports. The switch can be
configured for per-VLAN (1x1) mode or Flat mode.
Models supported: OS6860, OS6860E, OS6900 and OS10K
Summary of the commands in this chapter is listed here:
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show erp
show erp statistics
show erp ring <ringid>
show erp statistics ring <ringId>
show erp port <chassis/slot/port>
debug qos internal "slot 1 list 1 verbose" | grep ERP
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20.1. Troubleshooting ERP on OmniSwitch
ERP is disabled by default.
Below is the command to verify the overall ERP status:
-> show erp
Below is an example (default):
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