Setup Guide
Dynamic ingress buering enables the sending of pause frames at dierent thresholds based on the number of ports that experience
congestion at a time. This behavior impacts the total buer size used by a particular lossless priority on an interface. The pause and resume
thresholds can also be congured dynamically. You can congure a buer size, pause threshold, ingress shared threshold weight, and
resume threshold to control and manage the total amount of buers that are to be used in your network environment.
Buer Sizes for Lossless or PFC Packets
You can congure up to a maximum of 4 lossless (PFC) queues. By conguring 4 lossless queues, you can congure 4 dierent priorities
and assign a particular priority to each application that your network is used to process. For example, you can assign a higher priority for
time-sensitive applications and a lower priority for other services, such as le transfers. You can congure the amount of buer space to be
allocated for each priority and the pause or resume thresholds for the buer. This method of conguration enables you to eectively
manage and administer the behavior of lossless queues.
Although the system contains 12 MB of space for shared buers, a minimum guaranteed buer is provided to all the internal and external
ports in the system for both unicast and multicast trac. This minimum guaranteed buer reduces the total available shared buer to 9.5
MB. This shared buer can be used for lossy and lossless trac.
The default behavior causes up to a maximum of 6.6 MB to be used for PFC-related trac. The remaining approximate space of 1 MB can
be used by lossy trac. You can allocate all the remaining 1 MB to lossless PFC queues. If you allocate in such a way, the performance of
lossy trac is reduced and degraded. Although you can allocate a maximum buer size, it is used only if a PFC priority is congured and
applied on the interface.
The number of lossless queues supported on the system is dependent on the availability of total buers for PFC. The default conguration
in the system guarantees a minimum of 52 KB per queue if all the 128 queues are congested. However, modifying the buer allocation per
queue impacts this default behavior.
By default the total available buer for PFC is 6.6 MB and when you congure dynamic ingress buering, a minimum of least 52 KB per
queue is used when all ports are congested. By default, the system enables a maximum of 1 lossless queue on the switch.
This default behavior is impacted if you modify the total buer available for PFC or assign static buer congurations to the individual PFC
queues.
Conguring the Dynamic Buer Method
Priority-based ow control using dynamic buer spaces is supported on the switch.
To congure the dynamic buer 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 Congure the shared PFC buer size and the total buer size. A maximum of 4 lossless queues are supported.
CONFIGURATION mode
dcb pfc-shared-buffer-size 2000
dcb pfc-total-buffer-size 5000
3 Congure the number of PFC queues.
CONFIGURATION mode
dcb enable pfc-queues pfc-queues
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Data Center Bridging (DCB)