Dell Brocade G620 Brocade 8.0.1 Fabric OS Troubleshooting and Diagnostics Guid - Page 74

Buffer credit issues, Getting out of buffer-limited mode

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ISL Trunking Symptom A link that is part of an ISL trunk failed. To correct this issue, connect additional ISLs to the switch with which you want to communicate. ∙ The ports are not the same speed or they are not set to an invalid speed. Manually set port speeds to a speed supported on both sides of the trunk. ∙ The ports are not set to the same long distance mode. Set the long distance mode to the same setting on all ports on both sides of the trunk. ∙ Local or remote ports are not in the same port group. Move all ISLs to the same port group. The port groups begin at port 0 and are in groups of 4 or 8, depending on the switch model. Until this is done, the ISLs do not trunk. ∙ The difference in the cable length among trunked links is greater than the allowed difference. Buffer credit issues This section describes a trunk going online and offline or hosts not being able to talk to a storage device. Symptom Probable cause and recommended action Trunk goes offline and online (bounces). A port disabled at one end because of buffer underallocation causes all the disabled ports at the other end to become enabled. Some of these enabled ports become disabled because of a lack of buffers, which in turn triggers ports to be enabled once again at the other end. While the system is stabilizing the buffer allocation, it warns that ports are disabled because of a lack of buffers, but it does not send a message to the console when buffers are enabled. The system requires a few passes to stabilize the buffer allocation. Ultimately, the number of ports for which buffers are available come up and stabilize. You should wait for stabilization, and then proceed with correcting the buffer allocation situation. Getting out of buffer-limited mode Occurs on LD_Ports. 1. Change the LD port speed to a lower speed (of non-buffer limited ports). 2. Change the LD port's estimated distance to a shorter distance (of non-buffer limited ports). 3. Change LD back to L0 (of non-buffer limited ports). 4. If you are in buffer-limited mode on the LD port, then increase the estimated distance. 5. Enable any of these changes on the buffer-limited port or switch by issuing the commands portDisable and portEnable . Brocade Fabric OS Troubleshooting and Diagnostics Guide 74 53-1004126-01

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Symptom
A link that is part of an ISL trunk failed.
To correct this issue, connect additional ISLs to the switch with
which you want to communicate.
∙
The ports are not the same speed or they are not set to an
invalid speed.
Manually set port speeds to a speed supported on both sides of
the trunk.
∙
The ports are not set to the same long distance mode.
Set the long distance mode to the same setting on all ports on
both sides of the trunk.
∙
Local or remote ports are not in the same port group.
Move all ISLs to the same port group. The port groups begin at
port 0 and are in groups of 4 or 8, depending on the switch
model. Until this is done, the ISLs do not trunk.
∙
The difference in the cable length among trunked links is
greater than the allowed difference.
Buffer credit issues
This section describes a trunk going online and offline or hosts not being able to talk to a storage device.
Symptom
Trunk goes offline and online (bounces).
Probable cause and recommended action
A port disabled at one end because of buffer underallocation causes all
the disabled ports at the other end to become enabled. Some of these
enabled ports become disabled because of a lack of buffers, which in turn
triggers ports to be enabled once again at the other end.
While the system is stabilizing the buffer allocation, it warns that ports are
disabled because of a lack of buffers, but it does not send a message to
the console when buffers are enabled. The system requires a few passes
to stabilize the buffer allocation. Ultimately, the number of ports for which
buffers are available come up and stabilize. You should wait for
stabilization, and then proceed with correcting the buffer allocation
situation.
Getting out of buffer-limited mode
Occurs on LD_Ports.
1.
Change the LD port speed to a lower speed (of non-buffer limited ports).
2.
Change the LD port’s estimated distance to a shorter distance (of non-buffer limited ports).
3.
Change LD back to L0 (of non-buffer limited ports).
4.
If you are in buffer-limited mode on the LD port, then increase the estimated distance.
5.
Enable any of these changes on the buffer-limited port or switch by issuing the commands
portDisable
and
portEnable
.
ISL Trunking
Brocade Fabric OS Troubleshooting and Diagnostics Guide
74
53-1004126-01