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Understanding FIP Functions

Fibre Channel over Ethernet (FCoE) Initialization Protocol (FIP) performs four major functions:

  • FIP VLAN discovery: FCoE device FCoE nodes (ENodes) discover the FCoE VLANs on which to transmit and receive FIP and FCoE traffic.

  • FIP discovery: FCoE devices discover Fibre Channel (FC) switches to which they can connect.

  • Initialization: FCoE devices perform fabric login (FLOGI) and fabric discovery (FDISC) to create a virtual link with an FC switch.

  • Maintenance: The switch ensures that the virtual link between the FCoE device and the FC switch remains valid, and also that the link termination logout (LOGO) functions properly.

When you configure the switch as an FCoE-FC gateway (QFX3500 switch only, as a standalone switch or as a QFabric system Node device), it converts FIP requests and information from FCoE devices into FC requests and information and relays them to the FC switch. To FCoE devices, the gateway appears to be an FCoE forwarder (FCF) and presents virtual fabric port (VF_Port) interfaces to the server ENode. To FC switches, the gateway appears to be an FC device that supports N_Port ID virtualization (NPIV) and presents an N_Port interface to the FC switch F_Port interface. When you configure the switch as an FCoE transit switch, you do not configure FIP parameters on the switch.

FIP FLOGI, FDISC, and LOGO are similar to the same processes in the native FC protocol.

This topic describes:

FIP VLAN Discovery

The gateway supports FIP VLAN discovery. Host ENodes use FIP VLAN discovery to discover the FCoE VLANs on which they will send and receive FIP and FCoE traffic and on which they will establish a virtual link with the FC switch. This means FCoE devices do not need manually configured FCoE VLANs.

FIP VLAN discovery and notification takes place on the native VLAN that the FCoE device uses for Ethernet traffic:

  1. The ENode sends a FIP VLAN discovery request to a multicast address called ALL-FCF-MACs to which all FC switches and FCFs on the VLAN listen.

  2. The FC switches and FCFs respond on the native VLAN with a list of the FCoE VLANs that are available for login.

  3. The ENode selects an FCoE VLAN and continues the FIP process on that VLAN.

Except for FIP VLAN discovery, all other FIP and FCoE traffic runs on an FCoE VLAN.

Best Practice:

Only FCoE traffic is permitted on the FCoE VLAN. A native VLAN might need to carry untagged traffic of different types and protocols. Therefore, it is a good practice to keep the native VLAN separate from FCoE VLANs.

FIP Discovery

The FIP discovery process allows an FCoE device ENode MAC to locate (discover) the FC switches in the FCoE VLAN to which it belongs. The ENode selects an FC switch to log in to from the available FC switches. Either the ENode MAC or the FC switch can initiate the FIP discovery process.

Server ENode MACs initiate FIP discovery:

  1. When an ENode MAC comes online, it sends a multicast discovery solicitation message on its FCoE VLAN to a multicast address called ALL-FCF-MACs to which all FCFs (including the FCF functionality of FC switches) on the VLAN listen. The discovery solicitation message includes the ENode’s addressing mode and the maximum protocol data unit (PDU) size the ENode MAC uses for FCoE traffic.

    The ENode uses the globally unique ENode MAC address assigned to it by the converged network adapter (CNA) manufacturer as an identifier in the FIP frame header.

  2. The FCFs on the VLAN that have a similar supported addressing mode, match the maximum FCoE size, and can accept a login from the ENode reply to the discovery solicitation message by sending a solicited unicast discovery advertisement message to the soliciting ENode MAC.

  3. The ENode MAC compiles a list of FCFs that are available for login, selects an FCF (the FCF with the highest priority setting), and is then ready to log in to the FCF.

The FIP discovery process is similar when the FC switch or FCF initiates discovery:

  1. FCF MACs periodically send unsolicited multicast discovery advertisements on the FCoE VLAN to the ALL-ENode-MACs multicast address, to which all ENode MACs on the VLAN listen. The FIP keepalive advertisement period timer (FKA_ADV_PERIOD) controls the interval between multicast discovery advertisements. The multicast discovery advertisements inform ENodes on the VLAN that FCF VF_Ports are available for establishing virtual links with ENode VN_Ports.

  2. ENodes on the FCoE VLAN create an entry for the FCF-MAC in their FCF-MAC lists.

  3. An ENode can respond to the unsolicited multicast discovery advertisement with a unicast discovery solicitation message to the FCF.

  4. Upon receiving the ENode’s unicast discovery solicitation, the FCF replies with a unicast discovery advertisement sent to the ENode MAC.

After the ENode MAC selects an FCF to log in to, FIP initialization begins. To proceed from discovery to initialization, the server ENode addressing mode must match the FCF addressing mode and maximum FCoE size. In addition, the FCF must be configured to allow FIP FLOGI from that ENode.

FIP FLOGI

FIP initialization is the server ENode login process to the FCF after the ENode discovers the FCFs (including FC switches) on the FCoE VLAN:

  1. The ENode sends a fabric login (FLOGI) request message to the FCF.

  2. The FCF replies to confirm the ENode login and provides the ENode a locally unique MAC address to use for FCoE frame transactions. The locally unique MAC address identifies the VN_Port interface of the ENode for the session the login establishes. (The ENode continues to use the globally unique ENode MAC address for FIP frame transactions.)

The locally unique ENode MAC address for FCoE operations depends on whether the ENode address mode is configured as a fabric-provided MAC address (FPMA) or as a server-provided MAC address (SPMA; the gateway does not support ENodes in SPMA mode and rejects login attempts from ENodes in SPMA mode):

  • For FPMA mode, the FCF provides a MAC address to the ENode during the FIP FLOGI exchange. The FPMA MAC address is a 48-bit value that is unique to the local fabric and consists of a 24-bit FCoE mapped address prefix (FC-MAP) and a 24-bit FC identifier (FCID). You can configure the FC-MAP value on the FCF or use the default value of 0EFC00h. The FCoE device must use the same FC-MAP value as the FCF, or else discovery and login fail.

  • For SPMA mode, the server provides its MAC address to the FCF. The FCF compares the server MAC address to a list of addresses approved for FCoE access. The gateway does not support ENodes in SPMA mode.

Successful login instantiates a secure virtual link between the ENode and the FCF and terminates the FIP virtual link instantiation phase. The initiating server behind the ENode can exchange FC payloads with storage devices in the FC SAN by sending FCoE frames over the virtual link.

FIP FDISC

After an ENode successfully logs in to an FCF and establishes a virtual link, the ENode can request more virtual links (sessions) over the same physical link by sending a FIP fabric discovery (FDISC) request. FDISC allows the creation of multiple separate secure VN_Port virtual links on one physical link. Each virtual link receives a locally unique identifier from the FCF to enable security and separation between the VN_Port virtual links sharing a physical ENode port. This is called N_Port ID virtualization (NPIV).

FDISC is similar to FLOGI in that it requests a login and a unique ID from the FCF. The difference is that FLOGI obtains the initial login and ID for the physical link, whereas FDISC obtains additional logins and IDs so that multiple virtual links can share one physical link securely.

After a VN_Port FDISC is complete, the application using that VN_Port can send FCoE frames over the virtual link.

FIP Maintenance (Keepalive Messages)

Although FCoE protocol handles the payload communication between the initiating ENode and the target FC device, FIP continues to run in the background. FIP constantly updates ENode FCF lists by listening to the periodic FCF multicast discovery advertisements, and it verifies the ability to reach the FCF by transmitting periodic FIP keepalive advertisements.

The ENode sends periodic ENode FIP keepalive advertisements to the FCF with the ENode MAC address as the identifier. The ENode also sends periodic VN_Port FIP keepalive advertisements on behalf of each VN_Port on the ENode, using the VN_Port MAC address as the source MAC. The VN_Port FIP keepalive advertisements occur every 90 seconds. The keepalive advertisements reset the session timer for the virtual link connection to the FCF. If the FCF does not receive a keepalive advertisement for a logged-in ENode or VN_Port before the session timer expires, the virtual link is terminated.

The periodic unsolicited multicast discovery advertisements the FCF sends to the ALL-ENode-MACs address continuously verify that the FCF is still reachable. The ENode and the FCF periodic unsolicited multicast discovery advertisements occur at the configured FIP keepalive advertisement period interval (FKA_ADV_PERIOD) plus or minus a random offset to prevent a flood of simultaneous keepalive advertisements.

If the FCF does not receive the ENode keepalive advertisements before the FCF’s FIP keepalive timer expires, the FCF considers the virtual link to the ENode as “down” and terminates the virtual link to the ENode. The keepalive timer expires in 2.5 times the configured timer value. This also terminates any VN_Port virtual links instantiated by that ENode.

If the FCF does not receive a VN_Port keepalive advertisement before the FCF’s FIP keepalive timer expires, the FCF considers the virtual link to the VN_Port as “down” and terminates the virtual link to that VN_Port. The VN_Port keepalive timer expires in 2.5 times the configured timer value.

If the ENode does not receive the FCF unsolicited multicast discovery advertisement before the ENode’s FIP keepalive timer expires, the ENode considers the virtual link to the FCF as “down” and all of the VN_Port virtual links to that FCF on the ENode are terminated.

FIP LOGO

FIP handles ENode and VN_Port logout when a session is finished.

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