8.7. Fibre Channel over IP

Fibre Channel over IP, also known as Fibre Channel tunneling or storage tunneling, is an IP-based storage networking technology developed by the Internet Engineering Task Force. It enables Fibre Channel information to be transmitted by tunneling data between SAN facilities over IP networks. This capacity facilitates data sharing over a geographically distributed enterprise.

IP communications between nodes over Fibre Channel is achieved by creating a unidirectional exchange. For the receiving node to respond (bidirectional interaction), another exchange must be created.

Because IP addresses are 4 bytes and Fibre Channel address identifiers are 3 bytes, an Address Resolution Protocol (ARP) server must be available to allow mapping between the two addresses. Normally, the ARP server is implemented at the fabric level and has its own address (x 'FF FFFC').

An IP packet set is handled at the Fibre Channel level as a sequence. The maximum IP packet size is 65,280 bytes, which allows the packet and its 255 bytes of overhead to fit within a 64KB buffer.

If a frame error occurs, the default exchange error policy (abort, discard a single sequence) is to discard the packet with no retransmission. Subsequent sequences are not affected. Retransmission, if needed, is handled at the Internet Protocol (IP) and Transmission Control Protocol (TCP) levels and is transparent to the Fibre Channel.