Cisco MDS 9000 Series Configuration Manual page 182

Extended Receiver Ready
• If you had configured the buffer-to-buffer credits using the switchport fcrxbbcredit value mode E
command, and used the switchport vl-credit vl0 value vl1 value vl2 value vl3 value command to set
the new buffer-to-buffer credits values for the VLs, the sum of the configured buffer-to-buffer credits
for VLs are pushed to the switchport fcrxbbcredit value mode E command.
• Use the no switchport fcrxbbcredit value or switchport vl-credit default command to set the default
buffer-to-buffer credits value for the VLs.
• If you have configured the extended buffer-to-buffer credits using the switchport fcrxbbcredit extended
value in the Cisco MDS NX-OS Release 7.3(x) or earlier, upgraded to Cisco MDS NX-OS Release
8.1(1), and set the flow-control mode to ER_RDY, the extended buffer-to-buffer credits that are already
configured are distributed to the VLs in the following manner:
• If the buffer-to-buffer credits value that is configured is less than 50, the minimum values 5, 1, 4,
• If the buffer-to-buffer credits value that is configured is more than 34 and less than 50, the
• If the buffer-to-buffer credits value that is configured is more than 50, the minimum values 15, 15,
• If you are upgrading to or if you are in the Cisco MDS NX-OS Release 8.1(1), ER_RDY is enabled,
• You cannot configure regular buffer-to-buffer credits after you configure the extended buffer-to-buffer
credits. You must first disable the extended buffer-to-buffer credits using the no fcrxbbcredit extended
enable command and then configure the regular buffer-to-buffer credits.
• You cannot disable the extended buffer-to-buffer credits configuration even if one link is running in the
extended buffer-to-buffer credits mode.
Cisco MDS 9000 Series Interfaces Configuration Guide, Release 8.x
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initialization state because the control lane (VL0) is allocated 0 credits. To recover from this situation,
shutdown the link and allocate more than 34 buffer-to-buffer credits using the switchport
fcrxbbcredit value or allocate at least one buffer-to-buffer credit to VL0, using the switchport
vl-credit vl0 value vl1 value vl2 value vl3 value command.
Note
The sum of the buffer-to-buffer credits configured for VLs cannot exceed 500.
and 40 are allocated to VL0, VL1, VL2, and VL3 respectively.
buffer-to-buffer credits get distributed in the ratio 5:1:4:40.
4, and 430 are allocated to VL0, VL1, VL2, and VL3 respectively. The remaining buffer-to-buffer
credits are distributed in the ratio 30:30:100:3935 (VL0:VL1:VL2:VL3).
and the buffer-to-buffer credits value configured is less than 34, the VLs are stuck in the initialization
state because the control lane (VL0) is allocated 0 credits. To recover from this situation, shutdown
the link and allocate more than 34 buffer-to-buffer credits using the switchport fcrxbbcredit value
or allocate at least one buffer-to-buffer credit to VL0, using the switchport vl-credit vl0 value vl1
value vl2 value vl3 value command.
Note The sum of the extended buffer-to-buffer credits configured for VLs cannot
exceed 4095 on a Cisco MDS 9700 16-Gbps Fibre Channel Switching Module,
and 8270 on a Cisco MDS 9700 48-Port 32-Gbps Fibre Channel Switching
Module.
Congestion Detection, Avoidance, and Isolation