Concept Guide
Figure 29. Illustration of Trac Congestion
The system supports loading two DCB_Cong les:
• FCoE converged trac with priority 3.
• iSCSI storage trac with priority 4.
In the Dell EMC Networking OS, PFC is implemented as follows:
• PFC is supported on specied 802.1p priority trac (dot1p 0 to 7) and is congured per interface. However, only two lossless queues
are supported on an interface: one for Fibre Channel over Ethernet (FCoE) converged trac and one for Internet Small Computer
System Interface (iSCSI) storage trac. Congure the same lossless queues on all ports.
• PFC supports buering to receive data that continues to arrive on an interface while the remote system reacts to the PFC operation.
• PFC uses DCB MIB IEEE 802.1azd2.5 and PFC MIB IEEE 802.1bb-d2.2.
• A dynamic threshold handles intermittent trac bursts and varies based on the number of PFC priorities contending for buers, while a
static threshold places an upper limit on the transmit time of a queue after receiving a message to pause a specied priority. PFC trac
is paused only after surpassing both static and dynamic thresholds for the priority specied for the port.
• By default, PFC is enabled when you enable DCB. If you have not loaded FCoE_DCB_Cong and iSCSI_DCB_Cong, DCB is disabled.
When you enable DCB globally, you cannot simultaneously enable link-level ow control.
• Buer space is allocated and de-allocated only when you congure a PFC priority on the port.
Enhanced Transmission Selection
Enhanced transmission selection (ETS) supports optimized bandwidth allocation between trac types in multiprotocol (Ethernet, FCoE,
SCSI) links.
ETS allows you to divide trac according to its 802.1p priority into dierent priority groups (trac classes) and congure bandwidth
allocation and queue scheduling for each group to ensure that each trac type is correctly prioritized and receives its required bandwidth.
For example, you can prioritize low-latency storage or server cluster trac in a trac class to receive more bandwidth and restrict best-
eort LAN trac assigned to a dierent trac class.
NOTE
: Use the following command to enable etsacl: cam-acl l2acl 2 ipv4acl 2 ipv6acl 0 ipv4qos 0 l2qos 0
l2pt 0 ipmacacl 0 vman-qos 0 fcoeacl 2 etsacl 3. After executing this command, you must save the
conguration and then reload the system.
The following gure shows how ETS allows you to allocate bandwidth when dierent trac types are classed according to 802.1p priority
and mapped to priority groups.
Data Center Bridging (DCB)
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