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What Is Fibre Channel Over IP?

Gary Fisher, mainframe connectivity consultant, IBM Lab Services, explains what Fibre Channel over IP (FCIP) is.

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Q: What is Fibre Channel over IP?

Fibre Channel over IP (FCIP) is a method to carry SAN traffic over long distances using a TCP/IP network.

The Fibre Channel Protocol (FCP) expanded on Enterprise System Connection (ESCON)—the first SAN—to fit the needs of I/O for open systems (Linux* variants and Windows*). Fibre Connection (FICON) is FCP with restrictions that satisfy the I/O requirements of mainframe OSes (e.g., z/OS*, z/VM and z/TPF). 

ESCON Directors, FICON Directors and FCP SAN switches simplify connecting multiple host processors and storage. Node ports (N_Ports) are what FCP calls the Host Bus Adapters and I/O Adapters. Fabric ports (F_Ports) are SAN switch ports that dynamically connect to pass I/O traffic.

FCP simplified ESCON, which required more links, by adding connections between SAN switches using Expansion ports (E_Ports), that attach to Inter Switch Links (ISLs). ISLs increase the possible connections and simplify physical connections, especially in a data center with multiple rooms such as in a campus environment.

Generally, ISLs are physically limited to 10 km maximum distance. Techniques that enable communicating with a device that’s relatively far away exist for both synchronous and asynchronous I/O, depending on the distances involved and the capability of an application to tolerate the latency.

It’s increasingly common to see multiple data centers connected for durability and disaster recovery separated by much more than 10 km. FCIP is one of several methods to connect SAN switches at longer distances. FCIP uses a network to carry I/O. It encapsulates the Fibre channel I/O frames in TCP/IP segments, routes them through a WAN, and un-encapsulates them at the destination SAN switch as if they came through an ISL. An FCIP connection has its feet in two environments: it presents the appearance of a virtual E_Port (VE_Port) to the other F_Ports in the SAN, and of an Ethernet port to the network.

Many techniques exist for data replication, which is now essential for disaster recovery. Some devices communicate without host intervention using FCP over a SAN, with intervening ISLs if necessary, and with the ISLs over FCIP if so configured. 

An FCP connection for replication can be made through physically separate SAN switches from the host SAN, or logically separated, which presents E_Ports in different logical environments but shares the physical Gigabit Ethernet connections. Thus, a pair of SAN switches and connected IP routers can carry both replication traffic and I/O to remote devices using FCIP. 

FCIP is a proven part of the toolkit to provide SAN-based I/O and replication connectivity in a multisite data center environment.

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