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Understanding Fibre Channel

 

Fibre Channel (FC) is a serial I/O interconnect network technology capable of supporting multiple protocols. It is used primarily for storage area networks (SANs). The committee standardizing FC is the International Committee for Information Technology Standards (INCITS).

When configured as a Fibre Channel over Ethernet (FCoE)-FC gateway, the QFX3500 switch supports the transport of native FC traffic between FC switches and the gateway’s native FC interfaces.

Note

Only the QFX3500 switch has native FC ports and supports native FC connection to the SAN. Only the QFX3500 can be configured as an FCoE-FC gateway, and only as a standalone switch or as a QFabric system Node device. FCoE-FC gateway configuration is not supported in Virtual Chassis or Virtual Chassis Fabric configurations.

FC concepts include:

FC Fabrics

An FC fabric is a switched network topology that interconnects FC devices using FC switches, usually to create a SAN. An FC switch is a Layer 3 network switch that is compatible with the FC protocol, forwards FC traffic, and provides FC services to the components of the FC fabric. FC devices are usually servers or storage devices such as disk arrays.

Switches called FCoE forwarders (FCFs) perform a subset of FC switch functions. An FCF is a Layer 3 network switch that is compatible with the FC protocol and forwards FC traffic, but does not provide network services.

When configured as an FCoE-FC gateway, the QFX3500 switch acts a proxy for the FCF functionality of an FC switch. The gateway provides FCoE devices on the Ethernet network access to the FC network without requiring the FC switches in the SAN to support Ethernet interfaces. The gateway is not an FCF and does not provide FC services.

FC network design often uses two fabrics (dual-rail topology) for redundancy. The two fabrics connect to edge devices but are otherwise unconnected, so that if one fabric goes down, the other fabric can continue to provide connectivity.

FC Port Types

The QFX3500 switch supports the following FC port types:

  • N_Port—An N_Port is a port on the node of an FC device such as a server or a storage device and is also known as a node port.

  • F_Port—An F_Port is a port on an FC switch that connects to an FC device N_Port in a point-to-point connection. F_Ports are also known as fabric ports.

These port types are a subset of the existing FC port types that can be supported in an FC fabric.

FC Switches

FC switches provide FC services to the FC network. FC switches forward Layer 3 traffic. They may transport a combination of native FC traffic and other traffic, such as Internet Small Computer Systems Interface (iSCSI) or FCoE, or they may transport only native FC traffic. When an FC switch supports FCoE, it combines FCoE termination functions with the FC stack on an FC switching element. This is also known as a dual-stack switch.

When FC switches support FCoE, they present virtual FC interfaces in the form of virtual F_Ports (VF_Ports) to the FCoE nodes (ENodes) on FCoE devices. A VF_Port is an endpoint in a virtual point-to-point connection with an ENode virtual N_Port (VN_Port). A VF_Port emulates a native FC F_Port and performs similar functions. A VF_Port is an intermediate port in a connection between an FCoE device such as a server in the Ethernet network and a storage device in the FC SAN.

FC switches that support FCoE contain at least one lossless Ethernet media access controller (MAC) paired with an FCoE controller. The lossless Ethernet MAC implements Ethernet extensions to avoid frame loss due to congestion. The FCoE controller instantiates and terminates virtual port instances as they are needed. Each VF_Port instance has one unique virtual link to an ENode VN_Port.

FCoE support also requires one FCoE Link End Point (LEP) for each VF_Port connection. An FCoE LEP is a virtual FC interface mapped onto the physical Ethernet interface. It transmits and receives FCoE frames on the virtual link, and handles FC frame encapsulation for traffic going from the FC switch to the FCoE device and frame de-encapsulation of traffic received from the FCoE device.

When you configure the QFX3500 switch as an FCoE-FC gateway, the gateway performs these FC-to-Ethernet and Ethernet-to-FC conversion functions so that the FC switch does not need Ethernet (FCoE) ports.

Adapters

FC host bus adapters (HBAs) in FC switches and devices perform functions similar to those of Ethernet adapters in Ethernet switches and devices. Switches that perform FCoE functions and FCoE devices have converged network adapters (CNAs) that support both native FC and Ethernet functionality.

N_Port ID Virtualization (NPIV)

FC requires a unique point-to-point link between the FC switch (F_Port) and each host N_Port. In order to avoid using one physical link for each F_Port to N_Port connection, the port connections must be virtualized so that they can share a physical link while maintaining logical separation.

FC accomplishes this by enabling you to create an independent virtual link for each FC session by mapping each session to a virtualized N_Port. This process is called N_Port ID virtualization (NPIV).

NPIV makes each virtual link look like a dedicated point-to-point link. In this way, multiple FC devices and multiple applications or virtual machines (VMs) on a single FC device can connect to an FC switch using one physical port instead of using a physical port for each connection. The virtual link creates a secure boundary between traffic from different sources on a single physical connection.

NPIV works by creating a unique virtual port identifier for each logical connection on a physical port. Conceptually, this is similar to splitting a single physical interface into multiple logical interfaces or subinterfaces. A virtual port identifier consists of the port’s unique worldwide name (WWN) combined with a Fibre Channel ID (FCID) that the FC switch assigns to the virtual connection. This creates a virtual host bus adapter (HBA) for each virtual link that uniquely identifies the link to the FC switch.

FC Services

When you configure the QFX3500 switch as an FCoE-FC gateway, the gateway connects FCoE devices in the Ethernet network to the FC fabric. The gateway does not provide FC services directly. The gateway logs in to the FC fabric and obtains FC services from the FC fabric, including:

  • Management servers

    • Zone server—Defines which devices can connect to each other in the FC fabric.

    • Fabric configuration server—Discovers FC fabric topology and attributes.

    • Policy server—Distributes the rules for administering, managing, and controlling access to FC fabric resources.

    • HBA management server—Registers HBA information with the FC fabric.

  • Domain manager—Allocates domain IDs to virtual switches.

  • Fabric login server—Provides login services to the gateway so that the native FC ports on the gateway can perform initial fabric login (FLOGI) to the FC fabric and subsequent fabric discovery (FDISC) logins for the physical and virtual ports on the FCoE devices in the Ethernet network. This includes allocating Fibre Channel IDs (FCIDs) to ports.

  • Name server—Discovers, registers, and unregisters N_Port attributes, including the attributes of the native FC ports on the gateway that connect to the FC fabric.

  • Event server—Validates incoming events to ensure transaction integrity.

  • Time server—Maintains a common time for devices in the FC fabric.

  • Fabric controller

    • Fabric Shortest Path First (FSPF)—The FC fabric provides link-state path selection to the gateway.

    • State change notification (SCN) / registered state change notification server (RSCN)—Notifies the appropriate nodes when new devices come online, when other nodes fail, or when changes on an online node affect system operation.