Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 543)

Multi-Service IronWare Switching Configuration Guide 513
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Ethernet Ring Protection
15
Using standalone ERP
When using standalone ERP, all devices have a role, and all devices participate at least as ERP
members.
Ring-APS (R-APS) messages are sent at initial start-up of a configuration and periodically when link
or node failures or recoveries occur. Each ERN applies the information received in the R-APS
messages and forwards the received RAPS messages if both ports are in the forwarding state.
The sending ERN terminates the message when it receives a message originally sent from itself.
Configurable timers prevent ERNs from receiving outdated messages and decrease failure
reporting time to allow increased stability within the topology.
To properly configure and troubleshoot ERP, an understanding of the messaging, operational
states, and timers is essential. For more information about the ERP protocol, see ITU-T G.8032.
Using ERP with IEEE 802.1ag support
When you have other nonparticipating switches in the ring, you can use the IEEE 802.1ag support
to perform link health checks to the next ERN.
With IEEE 802.1ag configured, the ERNs within the ring send Continuity Check Messages (CCM) to
verify the integrity of their own links. If a node is not receiving CCMs or if a link goes down, a failure
is reported to the ring through R-APS messages. See
Figure 125 .
FIGURE 125 ERP with IEEE 802.1ag support
Figure 125 shows a segment with ERNs 3 and 4 and two non-participating switches located on the
same network segment between them. When ERNs 3 and 4 stopped receiving CCMs, the following
actions occurred on ERNs 3 and 4:
1. Blocked the failed port
2. Transmitted a R-APS (SF) message
3. Unblocked the non-failed port
4. Flushed the FDB
5. Entered the Protection state