data center bridging (DCB)

Data center bridging (DCB) is a collection of standards developed by a task force within the Institute of Electrical and Electronics Engineers (IEEE) 802.1 Working Group to create a converged data center network infrastructure using Ethernet as the unified fabric.

Data centers typically have multiple application-specific networks that run on separate link layer technologies, such as Fibre Channel (FC) for storage and Ethernet for connecting to a local area network (LAN). The IEEE Data Center Bridging Task Group created enhancements to 802.1 bridge specifications with the goal of enabling a lossless transport over Ethernet and a converged network where all data center applications could run over the same physical infrastructure.

The potential benefits of a converged data center network include:

  • Simpler management with only one fabric to deploy, maintain and upgrade.
  • Reliable Ethernet transport services for workloads that do not tolerate loss.
  • Lower costs because common adapters, cables and switches could be used.

DCB standards

The first set of standards completed by the Data Center Bridging Task Group was as follows:

Priority-based Flow Control (PFC): Provides a link level, flow control mechanism that can be independently controlled for each priority to eliminate data frame loss due to converged network congestion.

The IEEE 802.1Qbb Priority-based Flow Control standard defined the operation of PFC. In conjunction with that standard, the IEEE 802.3bd Media Access Control Frame for Priority-based Flow Control standard amended IEEE 802.3 and defined the frame format to support IEEE 802.1Qbb Priority-based Flow Control. Both standards were approved on June 16, 2011.

Congestion Notification (CN): Provides end-to-end congestion management for protocols without built-in congestion control mechanisms, such as Fibre Channel over Ethernet (FCoE). It also benefits protocols with existing congestion management by providing more timely reactions to network congestion. The IEEE 802.1Qau Congestion Notification standard was approved on March 25, 2010.

Enhanced Transmission Selection (ETS): Provides a common management framework for bandwidth assignment to traffic classes, allowing allocation of bandwidth to the different types of traffic sharing a converged network. The IEEE 802.1Qaz Enhanced Transmission Selection standard was approved on June 16, 2011.

Data Center Bridging Exchange Protocol (DCBX): A discovery and capability exchange protocol used to convey capabilities and configurations of other data center bridging features between directly connected peers to ensure consistent configuration across the network. For instance, DCBX can be used to determine if two linked peer devices support PFC. DCBX can also be used to detect misconfiguration of a feature between linked peers. In addition, a DCBX device can use the information from its peer to configure its own DCB features to match the configuration of its linked peer.

DCBX is defined in IEEE 802.1Qaz and uses functionality provided by the Link Layer Discovery Protocol through IEEE 802.1AB.

The aforementioned standards were amendments to IEEE 802.1Q and have been incorporated into IEEE 802.1Q-2014 and IEEE 802.3-2015.

Bridged network standards for server virtualization

The Data Center Bridging Task Group subsequently worked on the following specifications to address the impact of server virtualization technology on bridged networks:

Edge Virtual Bridging: Enables the coordinated configuration and management of bridge services for virtual stations, and allows virtual stations to share a common bridge port to obtain the services of bridge relay. The 802.1Qbg Edge Virtual Bridging standard was approved on May 14, 2012 and is now incorporated into IEEE 802.1Q-2014.

Bridge Port Extension: Extends a bridge and the management of its objects beyond its physical enclosure using 802 LAN technologies and interoperable interfaces. The 802.1BR Bridge Port Extension was approved on May 14, 2012.

This was last updated in September 2016

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