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the amount of buffer space to be allocated for each priority and the pause or resume thresholds for the buffer. This method of
configuration enables you to effectively manage and administer the behavior of lossless queues.
Although the system contains 9 MB of space for shared buffers, a minimum guaranteed buffer is provided to all the internal and
external ports in the system for both unicast and multicast traffic. This minimum guaranteed buffer reduces the total available
shared buffer to 7,787 KB. This shared buffer can be used for lossy and lossless traffic.
The default behavior causes up to a maximum of 6.6 MB to be used for PFC-related traffic. The remaining approximate space of
1 MB can be used by lossy traffic. You can allocate all the remaining 1 MB to lossless PFC queues. If you allocate in such a way,
the performance of lossy traffic is reduced and degraded. Although you can allocate a maximum buffer size, it is used only if a
PFC priority is configured and applied on the interface.
The number of lossless queues supported on the system is dependent on the availability of total buffers for PFC. The default
configuration in the system guarantees a minimum of 52 KB per queue if all the 128 queues are congested. However, modifying
the buffer allocation per queue impacts this default behavior.
By default the total available buffer for PFC is 6.6 MB and when you configure dynamic ingress buffering, a minimum of least
52 KB per queue is used when all ports are congested. By default, the system enables a maximum of two lossless queues on the
S4810 platform.
This default behavior is impacted if you modify the total buffer available for PFC or assign static buffer configurations to the
individual PFC queues.
Configuring PFC without a DCB Map
In a network topology that uses the default ETS bandwidth allocation (assigns equal bandwidth to each priority), you can also
enable PFC for specific dot1p-priorities on individual interfaces without using a DCB map. This type of DCB configuration is
useful on interfaces that require PFC for lossless traffic, but do not transmit converged Ethernet traffic.
Table 18. Configuring PFC without a DCB Map
Step Task Command Command Mode
1 Enter interface configuration mode on an Ethernet
port.
interface interface-
type}
CONFIGURATION
2 Enable PFC on specified priorities. Range: 0-7. Default:
None.
Maximum number of lossless queues supported on an
Ethernet port: 2.
Separate priority values with a comma. Specify a
priority range with a dash, for example: pfc priority
3,5-7
1. You cannot configure PFC using the pfc
priority command on an interface on which a
DCB map has been applied or which is already
configured for lossless queues (pfc no-drop
queues command).
pfc priority priority-
range
INTERFACE
Configuring Lossless Queues
DCB also supports the manual configuration of lossless queues on an interface when PFC mode is disabled in a DCB map, apply
the map on the interface. The configuration of no-drop queues provides flexibility for ports on which PFC is not needed, but
lossless traffic should egress from the interface.
Configuring no-drop queues is applicable only on the interfaces which do not need PFC.
Example:
Port A —> Port B
Data Center Bridging (DCB)
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