DCFM Enterprise User Manual (53-1001775-01, June 2010)

DCFM Enterprise User Manual 381

53-1001775-01

Bandwidth calculation during failover

In Figure 151, 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 151 Failover to a higher metric standby circuit

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. For example, assume the following:

• 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.

• If either circuit 0 or circuit 1 fails, traffic flows over the remaining circuit while the failed circuit

is being recovered. The available bandwidth is still considered to be 1.5 Gbps.

• If both circuit 0 and circuit 1 fail, there is a failover to circuits 2 and 3, and the available

bandwidth is updated as 2 Gbps.

• If a low metric circuit becomes available again, the high metric circuits go back to standby

status, and the available bandwidth is updated again. For example, if circuit 0 is recovered, the

available bandwidth is updated as 1 Gbps. If circuit 1 is also recovered, the available

bandwidth is updated as 1.5 Gbps.

7800

Circuit 1 - Metric 0 - Active

Circuit 2 - Metric 1 - Standby