Figure 285 e – Brocade 6910 Ethernet Access Switch Configuration Guide (Supporting R2.2.0.0) User Manual
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Brocade 6910 Ethernet Access Switch Configuration Guide
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Ethernet Ring Protection Switching
Ring nodes may be in one of two states:
Idle – normal operation, no link/node faults detected in ring
Protection – Protection switching in effect after identifying a signal fault
In Idle state, the physical topology has all nodes connected in a ring. The logical topology
guarantees that all nodes are connected without a loop by blocking the RPL. Each link is monitored
by its two adjacent nodes using Connectivity Fault Management (CFM) protocol messages.
Protection switching (opening the RPL to traffic) occurs when a signal failure message generated by
the Connectivity Fault Management (CFM) protocol is declared on one of the ring links, and the
detected failure has a higher priority than any other request; or a Ring – Automatic Protection
Switching protocol request (R-APS, as defined in Y.1731) is received which has a higher priority
than any other local request.
A link/node failure is detected by the nodes adjacent to the failure. These nodes block the failed
link and report the failure to the ring using R-APS (SF) messages. This message triggers the RPL
owner to unblock the RPL, and all nodes to flush their forwarding database. The ring is now in
protection state, but it remains connected in a logical topology.
When the failed link recovers, the traffic is kept blocked on the nodes adjacent to the recovered
link. The nodes adjacent to the recovered link transmit R-APS (NR - no request) message indicating
they have no local request. When the RPL owner receives an R-APS (NR) message it starts the
Wait-To-Recover (WTR) timer. Once WTR timer expires, the RPL owner blocks the RPL and transmits
an R-APS (NR, RB - ring blocked) message. Nodes receiving this message flush the forwarding
database and unblock their previously blocked ports. The ring is now returned to Idle state.
FIGURE 285
ERPS Ring Components
Configuration Guidelines for ERPS
1. Create an ERPS ring (
): The ring name is used as an index in the
G.8032 database.
2. Configure the east and west interfaces (
Configure Domain – Configure Details
): Each node on
the ring connects to it through two ring ports. Configure one port connected to the next node in
the ring to the east (or clockwise direction) and another port facing west in the ring.
East Port
West Port
RPL Owner
CC Messages
RPL
x
CC Messages
(Idle State)