Fibre Channel over Ethernet (FCoE) allows Fibre Channel traffic
to be encapsulated over a physical Ethernet link. FCoE and FIP 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, which means that in a congested network, Ethernet discards packets and relies
on higher level
protocols to provide retransmission and other reliability
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
Ethernet links on Cisco NX-OS
switches provide two mechanisms to ensure lossless transport for
FCoE traffic: link-level flow control 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 traffic on the link.
The priority flow control (PFC) feature on Cisco NX-OS platforms 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 using IEEE 802.1p traffic classes.