Fibre Channel over Ethernet (FCoE) is a standard of mapping of Fibre Channel frames over selected full duplex IEEE 802.3 networks. This allows Fibre Channel to leverage 10 Gigabit Ethernet networks while preserving the Fibre Channel protocol. The main application for FCoE is in the data centers.
FCoE essentially maps Fibre Channel natively over Ethernet while being independent of the Ethernet forwarding scheme. The FCoE protocol specification replaces the FC0 and FC1 layers of the Fibre Channel stack with Ethernet. By retaining the native fibre channel constructs, FCoE allows a seamless integration with existing Fibre Channel networks and management software.
In many data centers which use Ethernet for TCP/IP networks and Fibre Channel for storage area networks (SANs), with FCoE, Fibre Channel becomes another network protocol running on Ethernet, alongside traditional Internet Protocol (IP) traffic. This means FCoE runs alongside IP on Ethernet, unlike iSCSI which runs on top of IP using TCP. As FCoE does not use IP (Layer 3), it is not routable at the IP layer, and will not work across routed IP networks.
Enabling FCoE required 3 specific modifications to Ethernet in order to deliver the capabilities of Fibre Channel in SANs. This includes
- Encapsulation of a native fibre channel frame into an Ethernet Frame
- Extensions to the Ethernet protocol itself to enable a lossless ethernet fabric
- Replacing the fibre channel link with MAC addresses in a lossless Ethernet
Computers using FCoE use a Converged Network Adapter (CNA), which is both a Fibre Channel Host Bus Adapter (HBA) and an Ethernet Network Interface Card (NIC) to the server, but appears as a single Ethernet NIC to the network. Converged Network Adapters essentially provide an evolutionary approach to consolidation of a server's I/O over a single network (Ethernet) reducing network complexity in the Data Center.
FCoE is particularly useful for dense rack-mounted and blade servers in the data centers where cable simplification is the key requirement as well as for server virtualization which often requires many I/O connections per server.
With FCoE, network (IP) and storage (SAN) data traffic can essentially be consolidated with a single switch. Further, with the ability to combine Fibre Channel with 10 Gigabit Ethernet (GbE), companies can consolidate I/O, called unified I/O. This multifold consolidation
- reduced the number of network interface cards required to connect to disparate storage and IP networks
- reduces the number of cables and adapters,
- reduces the overall power and cooling costs
- increased utilization of the servers through server virtualization technologies.
Protocol Structure
The frame format of the FCoE is:
- The FC-Eth Ethertype indicates that FCoE is carried as Ethernet Payload.
- A two-bit Version field indicates the version of the FCoE protocol. This field shall be set to zero for this FCoE version. A received FCoE frame having a different version shall be treated as an erroneous frame.
- In order to cope with the minimum frame size mandated by Ethernet, a 10-bit FC Length (FC-LEN) field is provided and padding is added at the end of the FCoE frame when needed. The FC-LEN field shall be set to the length of the FC frame content expressed in 32-bit words.
- The FC-CRC is carried inside the Ethernet frame in addition to the Ethernet FCS to guarantee the Fibre Channel integrity.
- An Ethernet port receiving an FCoE frame with an invalid Ethernet FCS shall: 1) drop the FCoE frame (if possible); 2) keep the FCS invalid; or 3) change E-EOF to EOFni or EOFa to indicate that the FC frame content is invalid.
Related Protocols: SCSI, iFCP, FCP, FCIP, mFCP, iSCSI, TCP
Sponsor Source: FCoE is defined by a group under ANSI (www.ansi.org).
Reference: The project's homepage is http://www.t11.org/fcoe