Administrator Guide

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 9 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 7,787
KB. 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 two lossless queues on the S4810 platform.
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 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 specic dot1p-priorities on individual interfaces without using a DCB map. This type of DCB conguration is useful on interfaces that
require PFC for lossless trac, but do not transmit converged Ethernet trac.
Table 16.
Conguring PFC without a DCB Map
Step Task Command Command Mode
1 Enter interface conguration mode on an Ethernet port.
interface {tengigabitEthernet
slot/port |
fortygigabitEthernet slot/port}
CONFIGURATION
2 Enable PFC on specied 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 congure PFC using the pfc priority
command on an interface on which a DCB map has
been applied or which is already congured for lossless
queues (pfc no-drop queues command).
pfc priority priority-
range
INTERFACE
Conguring Lossless Queues
DCB also supports the manual conguration of lossless queues on an interface when PFC mode is disabled in a DCB map, apply the map on
the interface. The conguration of no-drop queues provides exibility for ports on which PFC is not needed, but lossless trac should
egress from the interface.
260
Data Center Bridging (DCB)