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Understanding Fibre Channel Terminology

 

To understand the Fibre Channel (FC) and Fibre Channel over Ethernet (FCoE) capabilities of the QFX Series, you should become familiar with the terms defined in Table 1.

Note

Support for FC or FCoE depends on the Junos OS release in your installation.

Table 1: Fibre Channel Terms

Term

Definition

addressing mode

Format for the locally unique MAC address the FC switch assigns to FCoE devices for FCoE transactions after FIP establishes a connection between an FCoE device and the FC switch. The two addressing modes are fabric-provided MAC address (FPMA) and server-provided MAC address (SPMA). The QFX Series supports only FPMA.

During FLOGI or FDISC, the ENode advertises the addressing modes it supports. If the FC switch supports an addressing mode that the ENode uses, the virtual link can be established, and the devices can communicate.

See also fabric-provided MAC address (FPMA) and server-provided MAC address (SPMA).

ALL-ENode-MACs

Well-known multicast MAC address to which all FCoE ENodes listen. FCFs send multicast FIP discovery advertisement messages and FIP keepalive messages to the ALL-ENode-MACs address so that ENodes can discover and maintain connections to FCFs. The hexadecimal format of the address is 01:10:18:01:00:01.

See also well-known address (WKA).

ALL-FCF-MACs

Well-known multicast MAC address to which all FCFs listen. ENodes send multicast FIP discovery solicitation messages to the ALL-FCF-MACs address to find out which FCFs can accept a login. The hexadecimal format of the address is 01:10:18:01:00:02.

See also well-known address (WKA).

congestion notification

See quantized congestion notification (QCN).

converged network adapter (CNA)

Physical adapter that combines the functions of a Fibre Channel host bus adapter (HBA) to process Fibre Channel frames and a lossless Ethernet network interface card (NIC) to process Ethernet frames. CNAs have one or more Ethernet ports. CNAs encapsulate Fibre Channel frames in Ethernet for FCoE transport and de-encapsulate Fibre Channel frames from FCoE to native Fibre Channel.

See also host bus adapter (HBA).

data center bridging (DCB)

Set of IEEE specifications that enhance the Ethernet standard to allow it to support converged Ethernet (LAN) and Fibre Channel (SAN) traffic on one Ethernet network. DCB features include priority-based flow control (PFC), enhanced transmission selection (ETS), Data Center Bridging Capability Exchange protocol (DCBX), quantized congestion notification (QCN), and full-duplex 10-Gigabit Ethernet ports.

See also priority-based flow control (PFC), Ethernet PAUSE, enhanced transmission selection (ETS), Data Center Bridging Capability Exchange protocol (DCBX), and quantized congestion notification (QCN).

expansion port (E_Port)

An expansion port in an FC switch/FCF that connects the FC switch/FCF to the E_Port of another FC switch/FCF to form an Interswitch Link (ISL) in a common FC fabric.

Data Center Bridging Capability Exchange protocol (DCBX)

Discovery and exchange protocol for conveying configuration and capabilities among neighbors to ensure consistent configuration across the network. It is an extension of the Link Layer Data Protocol (LLDP, described in IEEE 802.1AB)

See also data center bridging (DCB).

enhanced transmission selection (ETS)

Mechanism that provides finer granularity of bandwidth management within a link.

See also data center bridging (DCB).

ENode

See FCoE Node (ENode)

ENode MAC

Lossless Ethernet MAC paired with an FCoE controller in an ENode.

See also FCoE node (ENode).

ENode MAC address

Globally unique address assigned to the CNA by the manufacturer and used to identify the node for FIP transactions.

Ethernet PAUSE

As defined in IEEE 802.3X, a flow control mechanism that temporarily stops the transmission of Ethernet frames on a link for a specified period. A receiving element sends an Ethernet PAUSE frame when a sender transmits data faster than the receiver can accept it. Ethernet PAUSE affects the entire link, not just an individual flow. An Ethernet PAUSE frame temporarily stops all traffic transmission on the link and allows the receiver’s input buffer to empty sufficiently to restart traffic on the link. Ethernet PAUSE messages are sent to the previous hop and do not automatically propagate to the source of the congestion.

See also priority-based flow control (PFC).

fabric

Interconnection of network nodes using one or more network switches.

fabric discovery (FDISC)

Subsequent logins from the same ENode for different users, applications, or virtual machines after an ENode performs an initial FLOGI to log in to a switch.

FC and FIP FDISC messages serve the same function in FC and FCoE networks, respectively. N_Ports send FC FDISC messages to the FC switch and VN_Ports send FIP FDISC messages to the FCF.

After an N_Port acquires its initial N_Port ID through the FC FLOGI process, it can acquire additional N_Port IDs by sending an FC FDISC with a new worldwide port name and a source ID of 0x000000. The new port name and blank source ID tell the FC switch to assign a new N_Port ID to the N_Port. The different N_Port IDs allow multiple virtual machines or users on the N_Port to have separate, secure virtual links on the same physical N_Port. These additional ports are also referred to as VN_Ports.

FIP FDISC works the same way, except the VN_Port logs in using a FIP FLOGI message.

See also fabric login (FLOGI) and N_Port ID.

fabric login (FLOGI)

Creation of a logical connection to the FC switch and establishment of a node’s operating environment.

For FC devices, an N_Port logs in to the FC network by sending an FC FLOGI message to the F_Port of an FC switch.

For FCoE devices, a VN_Port logs in to the FC network by sending a FIP FLOGI message to the VF_Port of an FC switch.

fabric port (F_Port)

FC port on an FC switch or an FCF that connects point-to-point to an FC node port (N_Port) on an FC host (server or storage device). An F_Port provides access to fabric services for FC devices.

F_Ports are intermediate ports in a connection between FC device end-point N_Ports. For example, a connection between an FC host server and an FC storage device through an FC switch looks like this: FC server N_Port to FC switch ingress F_Port to FC switch egress F_Port to FC storage device N_Port.

See also node port (N_Port).

fabric-provided MAC address (FPMA)

MAC address that an FCF assigns to a single ENode MAC through the FLOGI or FDISC process that is unique to the local fabric. The FPMA uniquely identifies a single VN_Port at that ENode MAC in FCoE transactions with the FCF.

Because an ENode can have more than one ENode MAC, an FCF can assign multiple FPMAs to an ENode, one FPMA per ENode MAC.

An FPMA is a 48-bit value that consists of two 24-bit values, the N_Port ID and the FC-MAP value. The N_Port ID uniquely identifies the VN_Port and the FC-MAP value identifies the FCF.

See also FCoE node (ENode), N_Port ID, and FCoE mapped address prefix (FC-MAP).

FCF-MAC

Lossless Ethernet MAC paired with an FCoE controller in an FCF. The FCF-MAC enables the FCF to handle FCoE traffic.

FCoE controller

Instantiates and terminates VN_Port and VF_Port instances on an ENode. An ENode can have more than one FCoE controller. Each FCoE controller is paired with a lossless Ethernet MAC on the ENode.

See also lossless Ethernet MAC.

FC forwarder (FCF)

Alternative term and acronym to refer to an FC switch that has all physical Fibre Channel ports and the necessary set of services as defined in the T11 Organization Fibre Channel Switched Fabric (FC-SW) standards.

FCoE forwarder (FCF)

Defined by the Fibre Channel Backbone - 5 (FC-BB-5) Rev 2.00 specification available at http://www.t11.org/ftp/t11/pub/fc/bb-5/09-056v5.pdf as a device that has the necessary set of services as defined in FC-SW and the FCoE capabilities to act as an FCoE-based FC switch.

FCoE Initialization Protocol (FIP)

Layer 2 protocol for endpoint discovery, fabric login, and fabric association. FIP enables FCoE devices and FC switches to discover one another. Through FIP, FCoE nodes can log in to an FC switch, access the SAN FC fabric, and communicate with target FC devices. FIP messages also maintain the connection between the FCoE initiator and the FCF.

FIP has its own EtherType (0x8914) to distinguish its traffic from payload-carrying FCoE traffic and other Ethernet traffic.

FCoE link endpoint (LEP)

Virtual FC interface mapped onto a physical Ethernet interface to handle FC frame encapsulation and de-encapsulation and transmission and reception of FC frames encapsulated in Ethernet through a single virtual link.

FCoE mapped address prefix (FC-MAP)

24-bit value that identifies the FC switch and is half of the 48-bit FPMA MAC address. The FC-MAP value can be configured on the FC switch and has a default value of 0EFC00h. The FC-MAP value was originally called the Fibre Channel Organizationally Unique Identifier (FC-OUI).

See also fabric-provided MAC address (FPMA).

FCoE node (ENode)

Fibre Channel node that has one or more lossless Ethernet MACs, each paired with an FCoE Controller in order to transmit FCoE frames. An ENode combines FCoE termination functions and the FC stack on a CNA. ENodes present virtual FC interfaces to FC switches or FCFs in the form of VN_Ports, which can establish FCoE virtual links with FC switch/FCF VF_Ports. ENodes perform FCoE related functions in a converged network adapter (CNA).

See also converged network adapter (CNA).

FCoE-FC gateway

A form of N_Port virtualizer in which the node-facing ports are FCoE ports and the FC switch-facing ports are FC ports.

FCoE-FCoE gateway

A form of N_Port virtualizer in which the node-facing ports are FCoE ports and the FC switch-facing ports are FCoE ports.

FC-FC gateway

A form of N_Port virtualizer in which the node-facing ports are FC ports and the FC switch-facing ports are FC ports.

FCoE transit switch (also known as a FIP snooping bridge)

Switch that usually has a minimum set of features designed to support FCoE Layer 2 forwarding and FCoE security. The switch can also have optional additional features.

Minimum feature support is:

  • Priority-based flow control (PFC)

  • Data Center Bridging Capability Exchange Protocol (DCBX), including the FCoE application TLV

  • Enhanced transmission selection (ETS)

  • FIP snooping (minimum support is FIP automated filter programming at the ENode edge)

Note: A switch can perform FCoE transit functions without ETS or FIP snooping. Without FIP snooping, the FCoE gateway or CNA should filter non-FCoE traffic to Enodes.

Additional FIP snooping capabilities can include learning the virtual FC connection paths (VN2VF, VN2VN, or VE2VE) and monitoring the FIP keepalive mechanisms. Other optional capabilities can also enhance FCoE within the standards. FIP snooping is typically configurable on a per-VLAN basis.

A transit switch has an FC stack even though it is not an FC switch or an FCF.

FCoE VLAN

VLAN dedicated to carrying only FCoE traffic. FCoE traffic must travel in a VLAN. Only FCoE interfaces should be members of an FCoE VLAN. Ethernet traffic that is not FCoE traffic must travel in a different VLAN.

Fibre Channel

High-speed network technology used for storage area networks (SANs).

Fibre Channel fabric

Network of Fibre Channel devices that allows communication among devices, device name lookup, security, and redundancy.

Also a local fabric on a QFX3500 switch with FCoE interfaces connected to FCoE devices on the Ethernet network and native FC interfaces connected to an FC switch in a SAN.

Fibre Channel ID (FCID)

24-bit value the FC switch assigns to the N_Port or VN_Port as a unique identifier within the local FC network. The FCID consists of an 8-bit domain value, an 8-bit area value, and an 8-bit port value. The FCID is sometimes called an N_Port ID.

See also N_Port ID.

Fibre Channel over Ethernet (FCoE)

Standard for transporting FC frames over Ethernet networks. FCoE encapsulates Fibre Channel frames in Ethernet so that the same high-speed Ethernet physical infrastructure can transport both data and storage traffic while preserving the lossless CoS that FC requires. FCoE has its own EtherType (0x8906) to differentiate it from other Ethernet traffic.

FCoE runs on a DCB network. FCoE servers connect to a switch that supports both FCoE and native FC protocols. This allows FCoE servers on the Ethernet network to access FC storage devices in the SAN fabric on one converged network.

See also data center bridging (DCB).

Fibre Channel services

Functions required for establishing FC network connectivity among devices and for managing devices on the FC network, such as login servers, domain managers, name servers, and zone servers.

FC stack

FC or FCoE protocol capability implemented on a device to support the FC or FCoE functionality. Having an FC stack does not imply consuming a domain ID.

Each FC or FCoE enabled server or storage device has an FC stack. Similarly, an FC or FCoE switch, an FCF, an FCoE-FC gateway, and an FCoE transit switch have FC stacks.

Fibre Channel switch

Network switch that implements the Fibre Channel protocol.

FIP discovery advertisement

Multicast or unicast message that the FC switch (or FCF) transmits to ENodes to advertise the switch’s presence on the network so that ENodes can discover the switch and request to log in to the FC fabric.

The FC switch periodically sends multicast FIP discovery advertisements to the ALL-ENode-MACs address, a well-known address to which all ENodes listen. The multicast messages advertise the FC switch to all ENodes on the VLAN and serve as keepalive messages to maintain connectivity between the FC switch and ENodes.

When an ENode sends a FIP discovery solicitation message to the FC switch, the FC switch responds with a unicast FIP discovery advertisement to that ENode.

FIP discovery solicitation

Multicast or unicast message that an ENode transmits to FC switches (or FCFs) to find compatible switches in the network.

When an ENode initializes, it sends a multicast FIP discovery solicitation to the ALL-FCF-MACs address, a well-known address to which all FC switches and FCFs listen. Compatible switches reply with a unicast FIP discovery advertisement.

The ENode compiles a list of compatible switches, selects a switch, and logs in to that switch.

FIP keepalive

Periodic multicast FIP discovery advertisement sent from the FC switch or FCF to all ENodes to maintain connectivity.

FIP snooping

For VN_Port to VF_port (VN2VF) paths, FIP snooping is a security feature enabled for FCoE VLANs on an Ethernet switch that connects ENodes to FC switches or FCFs. FIP snooping inspects data in FIP frames and uses that data to create firewall filters. The filters permit only traffic from sources that perform a successful FLOGI to the FC switch. All other traffic on the VLAN is denied. FIP snooping filters are installed on the ports in the FCoE VLAN.

FIP snooping also applies similarly for VN_Port to VN_Port (VN2VN) and VE_Port to VE_Port (VE2VE) paths.

FIP snooping can also snoop to provide additional visibility of FCoE Layer 2 operation.

See also FCoE node (ENode).

FIP snooping bridge

See FCoE transit switch and FIP snooping.

host bus adapter (HBA)

Physical mechanism that connects a host system to other FC network and storage devices. HBAs have a unique worldwide node name (WWNN) for the HBA node, which all of the ports on the HBA share, and each port on an HBA has a unique worldwide port name (WWPN).

initiator

System component that originates an I/O command over an I/O bus or network. An FCoE server sending a request to an FC storage device is an example of an initiator.

iSCSI transit switch

Layer 2 Ethernet switch with a minimum set of best-practice Ethernet features to support iSCSI, along with optional enhancements. Minimum feature support is:

  • IEEE 802.3X asymmetric and symmetric flow control on ports not running in DCB mode

  • Priority-based flow control (PFC)

  • Enhanced transmission selection (ETS)

  • Data Center Bridging Capability Exchange Protocol (DCBX), including the iSCSI application TLV

Other capabilities such as Internet storage name service (iSNS) are optional.

Interswitch link (ISL)

The link between the E_Ports of two FC switches in a common FC fabric. When two FCoE-based FC switches are connected together, there is a virtual ISL through Layer 2.

logout (LOGO)

For FC devices, an N_Port logs out from the FC network by sending an FC LOGO message to the F_Port of an FC switch. The switch can also send a LOGO message to an N_Port to terminate its connection.

For FCoE devices, a VN_Port logs out from the FC network by sending a FIP LOGO message to the VF_Port of an FC switch. The switch can also send a LOGO message to a VN_Port to terminate its connection.

lossless Ethernet MAC

Full-duplex Ethernet MAC that implements Ethernet extensions to avoid Ethernet frame loss due to congestion and supports at least 2.5-KB jumbo frames. Each lossless Ethernet MAC combines with an FCoE Controller to perform FCoE termination functions on an ENode.

See also priority-based flow control (PFC), quantized congestion notification (QCN), FCoE controller, and FCoE node (ENode).

lossless Ethernet network

Ethernet network composed of only full-duplex links and lossless Ethernet MACs and with CoS and flow control to prevent dropping of frames.

lossless transport

In DCB networks, the ability to switch FCoE frames over an Ethernet network without dropping any frames. Lossless transports uses mechanisms such as priority-based flow control and quantized congestion notification to control traffic flows and avoid congestion.

N_Port ID

See Fibre Channel ID (FCID).

N_Port ID virtualizer

Presents itself as an FC or FCoE switch to external devices, but connects to an actual FC or FCoE switch in the other direction to provide the FC-SW services.

An N_Port ID virtualizer logs in to the actual FC or FCoE switch in the same way as a normal node device and uses the NPIV mechanism to proxy incoming FLOGIs to FDISCs on the actual FC or FCoE switch.

An N_Port ID virtualizes has an FC stack even though it is not an FC switch or an FCF.

The acronym NPV is commonly used for N_Port ID virtualizer even though the acronym is not defined in the standards.

N_Port ID Virtualization (NPIV)

NPIV enables a physical N_Port to acquire multiple N_Port IDs. Each N_Port ID maps to a different application (such as a virtual machine) or to a different user. This allows you to associate one F_Port with many N_Port IDs and create multiple discrete, secure virtual links over one physical point-to-point connection.

NPIV increases resource and bandwidth utilization and allows the implementation of access control, zoning, and port security on a per-application or per-user basis.

After an N_Port performs a FLOGI and receives its first N_Port ID, it can request more N_Port IDs by sending FDISC messages.

See also fabric login (FLOGI), fabric discovery (FDISC), and virtual link.

node port (N_Port)

N_Ports can be in two modes:

  • Fabric N_Port—Node port that is an FC host or storage device end port in a point-to-point link between the device and the F_Port of an FC switch. The point-to-point link can be virtual or physical.

  • Point-to-point N_Port—Node port that connects to another N_Port. The QFX3500 switch does not support this configuration.

N_Ports handle creation, detection, and flow of messages to and from the connected devices.

node worldwide name (NWWN)

WWN that is unique worldwide and is assigned to an FC node. An NWWN is valid for on multiple ports that are on that node (this identifies the ports as network interfaces of a particular node).

port mode

Role that the port plays in the FC fabric (endpoint device, FC switch connection to endpoint devices, interswitch link).

See also node port (N_Port), virtual node port (VN_Port), proxy node port (NP_Port), fabric port (F_Port), and virtual fabric port (VF_Port).

port worldwide name (PWWN)

WWN that is unique worldwide and is assigned to an FC port.

priority-based flow control (PFC)

Link-level flow control mechanism defined by IEEE 802.1Qbb that allows independent flow control for each class of service (as defined in the 3-bit CoS field of the Ethernet header by IEEE 802.1Q tags) to ensure that no frame loss from congestion occurs in DCB networks.

PFC is an enhancement of the Ethernet PAUSE mechanism, but PFC controls classes of flows, whereas Ethernet PAUSE indiscriminately pauses all of the traffic on a link. With PFC, a receiving device can signal a transmitting device to pause transmission based on traffic class.

PFC provides application-specific bandwidth reservations so you can ensure that time-critical protocols and applications such as FCoE receive the priority necessary to prevent frame loss. PFC allows the same physical link to carry FCoE traffic and provide lossless service while also carrying loss-tolerant Ethernet traffic.

See also Ethernet PAUSE.

proxy gateway mode

Connects FCoE initiators to FC switches in a converged Ethernet and Fibre Channel network and acts as an intermediary for these devices. The FCoE-FC gateway represents and acts for the FCoE initiators in transactions from the FCoE initiators destined for an FC switch, including converting FIP and FCoE frames to FC frames. The gateway represents and acts for an FC switch in transactions from the FC switch destined for an FCoE initiator, including converting FC frames to FIP frames and encapsulating FC frames in Ethernet.

proxy node port (NP_Port)

N_Port on the QFX Series that performs proxy functions when it is configured as an FCoE-FC gateway. The NP_Port acts as a proxy for the FCoE device VN_Ports in transactions with the FC switch.

quantized congestion notification (QCN)

Mechanism defined by IEEE 802.1Qau that manages network congestion within a Layer 2 domain. When a queue reaches a configured threshold, QCN throttles traffic at the source of the congestion by transmitting messages that propagate back to the source and temporarily stop the source from transmitting. When the queue crosses the threshold that indicates the congestion has dissipated, QCN sends a message to allow the source to resume transmitting frames.

session

Fabric login (FLOGI) or fabric discovery (FDISC) login to the FC SAN fabric. Session does not refer to end-to-end server-to-storage sessions.

server-provided MAC address (SPMA)

MAC address that an ENode assigns to one of its ENode MACs and is not assigned to any other ENode MAC in the same FCoE VLAN. An SPMA can be associated with more than one VN_Port at that ENode MAC.

The QFX Series does not support SPMA.

See also ENode MAC and fabric-provided MAC address (FPMA).

storage area network (SAN)

Network whose primary purpose is the transfer of data between computer systems and storage devices. This term is most commonly used in the context of any network that supports block storage, usually iSCSI, FC, and FCoE networks.

target

System component that receives an I/O command. An FC storage device that receives a request from a server is an example of a target.

VE_Port

Virtual ports created to form a connection (an interswitch link) between two FCoE-based FC switches as part of a common FC fabric.

VE2VE (VE_Port to VE_Port)

The Fibre Channel Backbone - 5 (FC-BB-5) Rev 2.00 specification capability of FCFs to connect to each other as a single FCoE FC SAN.

VN2VF (VN_Port to VF_Port)

The Fibre Channel Backbone - 5 (FC-BB-5) Rev 2.00 specification capability of an ENode to connect to an FCF or to an FCoE-enabled FC SAN.

VN2VN (VN_Port to VN_Port)

The Fibre Channel Backbone - 6 (FC-BB-6) specification capability of an ENode to connect directly over Layer 2 to another ENode without the need of any FC-related services. This capability is most often used in small-scale FCoE SANs.

virtual fabric port (VF_Port)

Data-forwarding component that emulates an F_Port. A VF_Port is dynamically instantiated on successful completion of a FIP FLOGI exchange and connects to one or more VN_Ports. The term virtual indicates the use of a non-FC link such as an FCoE link.

See also fabric port (F_Port).

virtual link

Logical link connecting two FCoE Link End Points (LEPs) over a lossless Ethernet network, for example, the link between a VF_Port and a VN_Port. The MAC addresses of the two LEPs identifies a virtual link.

See also FCoE link end point (LEP) and lossless Ethernet network.

virtual node port (VN_Port)

Data-forwarding component that emulates an N_Port. With FCoE, a VN_Port is dynamically instantiated on successful completion of a FIP FLOGI exchange and connects to one or more VF_Ports. The term virtual indicates the use of a non-FC link such as an FCoE link.

VN_Port is also used for the virtual N_Ports created in both FC and FCoE when additional NPIV-based logins occur over a previously created N_Port-to-VN_Port or N_Port-to-VF_Port connection.

See also node port (N_Port).

well-known address (WKA)

Address identifier used to access a service provided by an FC fabric. The service can be distributed in many elements throughout a fabric, or it can be centralized in one element. A WKA is always accessible, regardless of zoning. An example of a WKA is the ALL-FCF-MACs address to which all FCFs listen.

worldwide name (WWN)

64-bit identifier that is similar to a MAC address except that it is not used for forwarding. It uniquely identifies an FC device. The WWN is derived from the IEEE organizationally unique identifier (OUI) and vendor-supplied information. A WWN is unique worldwide.

worldwide node name (WWNN)

See node worldwide name (NWWN).

worldwide port name (WWPN)

See port worldwide name (PWWN).

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