Service Manual

The default behavior causes up to a maximum of 6.6 MB to be used for PFC-related trac. The remaining approximate space of 1
MB can be used by lossy trac. You can allocate all the remaining 1 MB to lossless PFC queues. If you allocate in such a way, the
performance of lossy trac is reduced and degraded. Although you can allocate a maximum buer size, it is used only if a PFC
priority is congured and applied on the interface.
The number of lossless queues supported on the system is dependent on the availability of total buers for PFC. The default
conguration in the system guarantees a minimum of 52 KB per queue if all the 128 queues are congested. However, modifying the
buer allocation per queue impacts this default behavior.
By default the total available buer for PFC is 6.6 MB and when you congure dynamic ingress buering, a minimum of least 52 KB
per queue is used when all ports are congested.
This default behavior is impacted if you modify the total buer available for PFC or assign static buer congurations to the
individual PFC queues.
Conguring the Dynamic Buer Method
Priority-based ow control using dynamic buer spaces is supported on the platform.
To congure the dynamic buer capability, perform the following steps:
1. Enable the DCB application. By default, DCB is enabled and link-level ow control is disabled on all interfaces.
CONFIGURATION mode
dcb enable
2. Congure the shared PFC buer size and the total buer size. A maximum of 4 lossless queues are supported.
CONFIGURATION mode
dcb pfc-shared-buffer-size
dcb pfc-total-buffer-size 5000
3. Congure the number of PFC queues.
CONFIGURATION mode
dcb enable pfc-queues pfc-queues
The number of ports supported based on lossless queues congured will depend on the buer. The default number of PFC
queues in the system is two for S4810 and Z9500, and one for S6000 platforms.
For each priority, you can specify the shared buer threshold limit, the ingress buer size, buer limit for pausing the
acceptance of packets, and the buer oset limit for resuming the acceptance of received packets.
4. Congure the prole name for the DCB buer threshold
CONFIGURATION mode
dcb-buffer-threshold dcb-buffer-threshold
5.
DCB-BUFFER-THRESHOLD mode
priority 0 buffer-size 52 pause-threshold 16 resume-offset 10 shared-threshold-weight 7
6. Assign the DCB policy to the DCB buer threshold prole.
CONFIGURATION mode
7. Assign the DCB policy to the DCB buer threshold prole on interfaces. This setting takes precedence over the default buer-
threshold setting.
INTERFACE mode (conf-if-te)
dcb-policy buffer-threshold buffer-threshold
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Data Center Bridging (DCB)