Users Guide

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 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 18. 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
pfc priority priority-
range
INTERFACE
252
Data Center Bridging (DCB)