Brocade Multi-Service IronWare Switching Configuration Gui Manual de usuario descargar pdf (Pagina 545)

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Multi-Service IronWare Switching Configuration Guide 515

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Ethernet Ring Protection

When an ERP topology starts up, each ERN (in Init state) transmits a R-APS (NR). After start-up, the

behavior varies by assigned role. Figure 127 shows the initialization process for an ERN.

FIGURE 127 Message exchange and actions during ERN initialization version 2

When the ring is in the Pending state, an ERN flushes the filtering database (FDB) if it receives any

of the following state requests:

• Signal-fail (SF)

• No request (NR), RPL Blocked (RB)

NOTE

ITU-T G.8032 Version 1 does not use a Pending state, so from the Protection state ERNs enter the

Idle state.

ERP timers

ERP provides various timers to ensure stability in the ring while a recovery is in progress or to

prevent frequent triggering of the protection switching. All of the timers are operator configurable.

• Guard timer — All ERNs use a guard timer. The guard timer prevents the possibility of forming a

closed loop and prevents ERNs from applying outdated R-APS messages. The guard timer

activates when an ERN receives information about a local switching request, such as after a

switch fail (SF), manual switch (MS), or forced switch (FS). When this timer expires, the ERN

begins to apply actions from the R-APS it receives. This timer cannot be manually stopped.

• Wait to restore (WTR) timer — The RPL owner uses the WTR timer. The WTR timer applies to the

revertive mode to prevent frequent triggering of the protection switching due to port flapping or

intermittent signal failure defects. When this timer expires, the RPL owner sends a R-APS (NR,

RB) through the ring.

• Wait to Block (WTB) timers — This wait-to-block timer is activated on the RPL owner. The RPL

owner uses WTB timers before initiating an RPL block and then reverting to the idle state after

operator-initiated commands, such as for FS or MS conditions, are entered. Because multiple

FS commands are allowed to co-exist in a ring, the WTB timer ensures that the clearing of a

single FS command does not trigger the re-blocking of the RPL. The WTB timer is defined to be

5 seconds longer than the guard timer, which is enough time to allow a reporting ERN to

transmit two R-APS messages and allow the ring to identify the latent condition.

When clearing a MS command, the WTB timer prevents the formation of a closed loop due to

the RPL owner node applying an outdated remote MS request during the recovery process.

RPL owner Non-RPL node RPL node

Init state Init state Init state

1Blocks the RPL

2Sends a R-APS (NR)

3 Enters the Pending state.

1 Blocks the left interface

2Sends a R-APS (NR)

3 Enters the Pending state

1Blocks the left interface

2Sends a R-APS (NR)

3 Enters the Pending state

4. Starts the WTR timer

5. (After the WTR expires) stops

sending NR

6. Sends R-APS (NR, RB, DNF)

7. Enters the Idle state

After receiving the (NR, RB, DNF) from

the RPL owner:

1 Unblocks the non-failed blocking

port

2 Stops sending (NR)

3 Enters the Idle state

After receiving the (NR, RB, DNF) from

the RPL owner:

1 Blocks the RPL port

2 Unblocks the other ports

3 Enters the Idle state

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