Users Guide

• In a switch stack, congure all stacked ports with the same PFC conguration.

A DCB input policy for PFC applied to an interface may become invalid if you recongure dot1p-queue mapping. This situation occurs when

the new dot1p-queue assignment exceeds the maximum number (2) of lossless queues supported globally on the switch. In this case, all

PFC congurations received from PFC-enabled peers are removed and resynchronized with the peer devices.

Trac may be interrupted when you recongure PFC no-drop priorities in an input policy or reapply the policy to an interface.

How Priority-Based Flow Control is Implemented

Priority-based ow control provides a ow control mechanism based on the 802.1p priorities in converged Ethernet trac received on an

interface and is enabled by default. As an enhancement to the existing Ethernet pause mechanism, PFC stops trac transmission for

specied priorities (CoS values) without impacting other priority classes. Dierent trac types are assigned to dierent priority classes.

When trac congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of the trac that needs to be

stopped. DCBx provides the link-level exchange of PFC parameters between peer devices. PFC creates zero-loss links for SAN trac that

requires no-drop service, while at the same time retaining packet-drop congestion management for LAN trac.

PFC is implemented on an Aggregator as follows:

• If DCB is enabled, as soon as a dcb-map with PFC is applied on an interface, DCBx starts exchanging information with PFC-enabled

peers. The IEEE802.1Qbb, CEE and CIN versions of PFC TLV are supported. DCBx also validates PFC congurations received in TLVs

from peer devices.

• To achieve complete lossless handling of trac, enable PFC operation on ingress port trac and on all DCB egress port trac.

• All 802.1p priorities are enabled for PFC. Queues to which PFC priority trac is mapped are lossless by default. Trac may be

interrupted due to an interface ap (going down and coming up).

• For PFC to be applied on an Aggregator port, the auto-congured priority trac must be supported by a PFC peer (as detected by

DCBx).

• A dcb-map for PFC applied to an interface may become invalid if dot1p-queue mapping is recongured. This situation occurs when the

new dot1p-queue assignment exceeds the maximum number (2) of lossless queues supported globally on the switch. In this case, all

PFC congurations received from PFC-enabled peers are removed and re-synchronized with the peer devices.

• Dell Networking OS does not support MACsec Bypass Capability (MBC).

Conguring Enhanced Transmission Selection

ETS provides a way to optimize bandwidth allocation to outbound 802.1p classes of converged Ethernet trac.

Dierent trac types have dierent service needs. Using ETS, you can create groups within an 802.1p priority class to congure dierent

treatment for trac with dierent bandwidth, latency, and best-eort needs.

For example, storage trac is sensitive to frame loss; interprocess communication (IPC) trac is latency-sensitive. ETS allows dierent

trac types to coexist without interruption in the same converged link by:

• Allocating a guaranteed share of bandwidth to each priority group.

• Allowing each group to exceed its minimum guaranteed bandwidth if another group is not fully using its allotted bandwidth.

To congure ETS and apply an ETS output policy to an interface, you must:

1 Create a Quality of Service (QoS) output policy with ETS scheduling and bandwidth allocation settings.

2 Create a priority group of 802.1p trac classes.

3 Congure a DCB output policy in which you associate a priority group with a QoS ETS output policy.

4 Apply the DCB output policy to an interface.

How Enhanced Transmission Selection is Implemented

Enhanced transmission selection (ETS) provides a way to optimize bandwidth allocation to outbound 802.1p classes of converged Ethernet

trac. Dierent trac types have dierent service needs. Using ETS, groups within an 802.1p priority class are auto-congured to provide

dierent treatment for trac with dierent bandwidth, latency, and best-eort needs.

Data Center Bridging (DCB)