Brocade Communications Systems Network Advisor 12.3.0, User Manual

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938 Brocade Network Advisor SAN User Manual
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FCIP trunking
22
FCIP circuit failover capabilities
Each FCIP circuit is assigned a metric, which is used in managing failover for FC traffic. Typically,
the metric will be either 0 or 1. If a circuit fails, FCIP Trunking tries first to retransmit any pending
send traffic over another lowest metric circuit. In
Figure 425 , circuit 1 and circuit 2 are both lowest
metric circuits. Circuit 1 has failed, and transmission fails over to circuit 2, which has the same
metric. Traffic that was pending at the time of failure is retransmitted over circuit 2. In order
delivery is ensured by the receiving Extension Switch or Blade.
FIGURE 425
Link loss and retransmission over peer lowest metric circuit
In Figure 426 , circuit 1 is assigned a metric of 0, and circuit 2 is assigned a metric of 1. In this
case, circuit 2 is a standby that is not used unless there are no lowest metric circuits available. If all
lowest metric circuits fail, then the pending send traffic is retransmitted over any available circuits
with the higher metric,
FIGURE 426
Failover to a higher metric standby circuit
You can configure a tunnel with standby metric 1 circuits that operate when all circuits configured
with metric 0 fail. However, these configurations can lead to condition where the tunnel is active,
but operating in a degraded mode because all metric 1 circuits (and failed metric 0 circuits) will not
be transferring tunnel data until all metric 0 circuits fail. Only at the point when all metric 0 circuits
fail, do available metric 1 circuits over data transfer. Consider configuring
“Circuit Failover
Grouping” to avoid this problem.
Bandwidth calculation during failover
The bandwidth of higher-metric circuits is not calculated as available bandwidth on an FCIP tunnel
until all lowest metric circuits have failed. Following is an example.
Assume the following configurations for circuits 0 through 3:
•
Circuits 0 and 1 are created with a metric of 0. Circuit 0 is created with a maximum
transmission rate of 1 Gbps, and circuit 1 is created with a maximum transmission rate of 500
Mbps. Together, circuits 0 and 1 provide an available bandwidth of 1.5 Gbps.
•
Circuits 2 and 3 are created with a metric of 1. Both are created with a maximum transmission
rate of 1 Gbps, for a total of 2 Gbps. This bandwidth is held in reserve.