Fibre Channel over Ethernet (FCoE) allows Fibre Channel traffic
to be encapsulated over a physical Ethernet link. FCoE frames use a
unique EtherType so that FCoE traffic and standard Ethernet traffic
can be carried on the same link.
Classic Ethernet is a best-effort protocol; in the event of
congestion, Ethernet will discard packets, relying on higher level
protocols to provide retransmission and other reliability
mechanisms. Fibre Channel traffic requires a lossless transport
layer; as a data storage protocol, it is unacceptable to lose a
single data packet. Native Fibre Channel implements a lossless
service at the transport layer using a buffer-to-buffer credit
For FCoE traffic, the Ethernet link must provide a lossless
service. Ethernet links on Cisco Nexus devices provide two mechanisms to ensure lossless transport for
FCoE traffic: link-level flow control (LL-FC) and priority flow
IEEE 802.3x link-level flow control allows a congested receiver
to signal the far end to pause the data transmission for a short
period of time. The pause functionality is applied to all the
traffic on the link.
The priority flow control feature applies pause
functionality to specific classes of traffic on the Ethernet link.
For example, PFC can provide lossless service for the FCoE traffic
and best-effort service for the standard Ethernet traffic. PFC can
provide different levels of service to specific classes of Ethernet
traffic (using IEEE 802.1p traffic classes).
switches support T11-compliant FCoE on all 10-Gigabit Ethernet interfaces.