Data Center Bridging (DCB) | 305
• Bandwidth allocated by the ETS algorithm is made available after strict-priority groups are serviced. If
a priority group does not use its allocated bandwidth, the unused bandwidth is made available to other
priority groups.
• For ETS traffic selection, an algorithm is applied to priority groups using:
• Strict-priority shaping
• ETS shaping
Credit-based shaping is not supported.
• ETS uses the DCB MIB IEEE 802.1azd2.5.
Data Center Bridging Exchange Protocol (DCBx)
The data center bridging exchange (DCBx) protocol is disabled by default on the S4810 and S4820T; ETS
is also disabled. DCBx allows a switch to automatically discover DCB-enabled peers and exchange
configuration information. PFC and ETS use DCBx to exchange and negotiate parameters with peer
devices. DCBx capabilities include:
• Discovery of DCB capabilities on peer-device connections
• Determination of possible mismatch in DCB configuration on a peer link
• Configuration of a peer device over a DCB link
DCBx requires the link layer discovery protocol (LLDP) to provide the path to exchange DCB parameters
with peer devices. Exchanged parameters are sent in organizationally specific type, length, values (TLVs)
in LLDP data units. For more information, refer to Chapter 29, Link Layer Discovery Protocol (LLDP).
The following LLDP TLVs are supported for DCB parameter exchange:
• PFC parameters: PFC Configuration TLV and Application Priority Configuration TLV.
• ETS parameters: ETS Configuration TLV and ETS Recommendation TLV.
Data Center Bridging in a Traffic Flow
The following figure shows how DCB handles a traffic flow on an interface.
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