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BP1037 Transitioning to DCB with EqualLogic PS series Storage Solutions 11
2.3.4 Data Center Bridging Capability Exchange (DCBx)
Datacenter Bridging Capability Exchange is an extension of the IEEE standard 802.1AB for Link Layer
Discovery Protocol (LLDP). It uses the existing LLDP framework for network devices to advertise their
identity and capabilities. LLDP relies on the use of Type-Length-Values (TLV) to advertise a device’s
capabilities for a multitude of Ethernet functions, as well as its identity. DCBx defines new TLVs specific
to the DCB functionalities. PFC and ETS have specific TLVs defining items such as:
• Whether PFC is to be used
• Priorities that will be managed using PFC
• Which priorities belong to a specific traffic class
• Bandwidth minimums for each defined traffic class
The standard also defines “Application” TLVs. These TLVs allow for the definition of which protocols
will be managed, as well as the priorities to be assigned to each. Currently FCoE and iSCSI have
Application TLVs; NAS will have a future TLV that will allow it to be DCB aware. For EqualLogic
environments using DCB, support for the iSCSI TLV is required. For FCoE, it is easy for the network to
assign a higher priority to its frames, as they have a separate EtherType. For iSCSI however, the end
station needs to know how to identify and isolate iSCSI frames from the other TCP/IP traffic. The iSCSI
TLV identifies what TCP port iSCSI traffic is using, so that the end station can properly assign the
desired class of service to all iSCSI packets. Once this has been defined, PFC and ETS can manage the
iSCSI traffic as its own class.
Figure 4 Data Centre Bridging Capability Exchange