Brocade Fabric OS Administrators Guide (Supporting Fabric OS v7.3.0) - Manual (Page 128)

Estimated maximum equally distributed distance = 1-port maximum distance/Number of ports
For example, for three ports running at 2 Gbps on a Brocade 300 switch, the maximum equally
distributed distance is calculated as 486 / 3 = 164 km.
Downgrade considerations
When Fabric OS firmware is downgraded from version 7.1 to an earlier version, the effect depends on
whether the number of buffer credits for the long-distance port is configured with the -framesize and -
distance options or with the -buffers option.
When a port is configured with -framesize and -distance options
In Fabric OS v7.1, if you configure the port by using the -distance option alone, the reserved buffers
are calculated according to the distance. If you configure both the -framesize option and the -
distance option, more buffers will be reserved, depending on the frame size.
With a firmware downgrade, those ports that were configured with more reserved buffers will keep the
reserved buffers as long as the ports remain online. The next time the port is toggled, buffers will again
be reserved on the basis of distance only.
When a port is configured with the -buffers option
A firmware downgrade is blocked when a port is configured as a long-distance port by means of the -
buffers option. The following warning message is displayed:
Downgrade to selected version is not allowed because few ports are configured with
Longdistance -buffers option. Please remove the configuration using
portcfglongdistance / L0 CLI or change the configuration with -distance
option on the console.
Configuring credits for a single VC
You can alter the default credit allocation for a normal distance E_Port or EX_Port so that a specific
number of credits is allocated to a port. When you allocate a specific number of credits to an E_Port or
EX_Port, the number of credits specified override the default credit allocation. When this feature is
disabled, the default credit model is restored. Only a normal distance E_Port and EX_Port can utilize
the new credit model, and the allocated credits are reserved only for that port.
When this feature is enabled, the E_Port credit configuration is persistent across system reboots and
High Availability (HA) failover.
This feature is supported on E_Ports and EX_Ports. It does not support ports configured as F_Ports,
Mirror Ports, L_Ports, and Longdistance Ports. If E_Port credits are configured on ports, you cannot
move the ports from one logical switch to another. This feature is not applicable on ICL_ports.
Increasing credits for normal distance E_Ports
Use the following steps to allocate credits to an E_Port.
Downgrade considerations
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