Bandwidth Calculation During Failover - Brocade Communications Systems 8 Administrator's Manual

In Figure
are in the same FCIP tunnel. 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 Failover between like metric circuits
or between different metric circuits is lossless.
FIGURE 6

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:
•
•
•
•
•
Fabric OS FCIP Administrator's Guide
53-1001766-01
6, circuit 1 is assigned a metric of 0, and circuit 2 is assigned a metric of 1. Both circuits
7800
Failover to a higher metric standby circuit
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 as each circuit comes online. 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.
Circuit 1 - Metric 0 - Active
Circuit 2 - Metric 1 - Standby
2
FCIP trunking
7800
13