Users Guide

Dynamic ingress buering enables the sending of pause frames at dierent thresholds based on the number of ports that experience
congestion at a time. This behavior impacts the total buer size used by a particular lossless priority on an interface. The pause and resume
thresholds can also be congured dynamically. You can congure a buer size, pause threshold, ingress shared threshold weight, and
resume threshold to control and manage the total amount of buers that are to be used in your network environment.
Buer Sizes for Lossless or PFC Packets
You can congure up to a maximum of 4 lossless (PFC) queues. By conguring 4 lossless queues, you can congure 4 dierent 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 congure the amount of buer space to be
allocated for each priority and the pause or resume thresholds for the buer. This method of conguration enables you to eectively
manage and administer the behavior of lossless queues.
Although the system contains 12 MB of space for shared buers, a minimum guaranteed buer is provided to all the internal and external
ports in the system for both unicast and multicast trac. This minimum guaranteed buer reduces the total available shared buer to 9.5
MB. This shared buer can be used for lossy and lossless trac.
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. By default, the system enables a maximum of 1 lossless queue on the switch.
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 switch.
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 2000
dcb pfc-total-buffer-size 5000
3 Congure the number of PFC queues.
CONFIGURATION mode
dcb enable pfc-queues pfc-queues
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Data Center Bridging (DCB)