Understanding FIP Implementation on an FCoE-FC Gateway

FIP Basics

FIP is enabled by default on all VLAN interfaces that belong to each FC fabric configured on the gateway. You can configure FIP parameters at a global level or on an individual interface. When you configure a parameter on an interface, it overrides the global configuration only for that interface. If you do not explicitly configure a FIP parameter, the gateway uses the default value.

In order for the gateway to connect FCoE devices with FCFs, the FIP parameters you configure on the gateway must be compatible with the parameters configured on the FC switch (for example, the FC-MAP values of the FC switch and of the FC fabric FIP configuration on the gateway must match, or the FC switch drops the frames).

When the NP_Ports on the gateway come up, they perform an FC FLOGI to the connected FC switch. Successful login establishes communication between the gateway and the FC switch, and gateway NP_Ports are marked for sending FDISC messages. Successful login also creates a next-hop entry in the gateway for the FC switch. If the FC switch rejects the FLOGI request, no link is established. The gateway maintains a list of valid FCF-MACs with which ENodes can connect.

After establishing communication with an FC switch, the gateway can connect FCoE devices in the Ethernet network to the FC switch. All of the subsequent connections the gateway makes with FC switches as a proxy for ENodes (on behalf of ENodes) are virtualized (NPIV) connections.

Fabric Login and FIP Login Overview

Figure 1 provides a brief overview of the FCoE-FC gateway fabric login to the FC switch and the FCoE device FIP login to the gateway.

Figure 1: FCoE-FC Gateway Fabric Login and FIP Login

The numbers in the following list correspond to the numbers in Figure 1 and briefly describe each step of the login process:

1. The FCoE-FC gateway NP_Port sends an FC fabric login (FLOGI) request to the FC switch F_Port.

2. The FC switch accepts the gateway FLOGI.

3. The gateway sends FIP multicast discovery advertisements on the FCoE VLAN (the gateway F_Port interface) to all connected FCoE device ENodes.

4. The FCoE device ENode sends a discovery solicitation message to the gateway.

5. The gateway responds with a unicast discovery advertisement to the ENode.

   Note:

   The gateway limits the number of discovery solicitations it accepts from FCoE devices to a maximum of 100 outstanding requests at any given time. If the gateway has 100 discovery solicitations outstanding, the gateway does not respond to new discovery solicitations. Instead, the gateway drops new discovery solicitations and reports the number of dropped discovery solicitations in the Dropped field of the show fibre-channel fip statistics command output. When there are fewer than 100 outstanding discovery solicitations, the system responds to new requests as usual with a discovery advertisement.

6. The FCoE device sends a FIP FLOGI or FIP FDISC message to the gateway.

7. The gateway converts the FIP FLOGI or FIP FDISC to an FC FDISC and forwards it to the FC switch to obtain a login for the FCoE device.

8. The FC switch responds to the FC FDISC by sending a new ID for the NPIV session to the gateway.

9. The gateway converts the FC FDISC response from the FC switch to a FIP FDISC response and forwards it to the FCoE device.

The following sections describe some of these steps in greater detail.

Proxy FIP Discovery

After the gateway establishes a connection with an FC switch:

1. The gateway sends periodic FIP multicast discovery advertisements on the FCoE VLAN so that ENodes can add the gateway to their FCF lists.

2. The ENode initializes and sends a multicast discovery solicitation message on the FCoE VLAN. If the ENode has already initialized and has a list of FCFs, it can send a unicast discovery solicitation message to a particular FCF such as the gateway.

   Note:

   The gateway limits the number of discovery solicitations it accepts from FCoE devices to a maximum of 100 outstanding requests at any given time. If the gateway has 100 discovery solicitations outstanding, the gateway does not accept new discovery solicitations until there are fewer than 100 discovery solicitations outstanding.

3. When the gateway receives a multicast discovery solicitation from an ENode, it responds by sending a unicast discovery advertisement to that ENode.

   When the gateway receives a unicast discovery solicitation from an ENode, it also responds with a unicast discovery advertisement to the ENode.

   To the ENode, the gateway appears to be an FCF.

The FIP discovery process adds the ENode to the gateway ENode database.

Proxy FIP Initialization

1. If the ENode chooses to log in to the gateway, it responds to the gateway’s unicast discovery advertisement by sending a login request in the form of a FIP FLOGI if it is the initial connection to the gateway. If the ENode already has an established session with the gateway and another application or virtual machine wants to connect to the gateway, the ENode sends a FIP FDISC to the gateway.

2. The gateway receives the FIP FLOGI or FIP FDISC from the ENode, converts it into an FC FDISC, and sends it through the least-loaded NP_Port to the FC switch on behalf of the ENode. The FC FDISC message requests an FCID for the new virtual link.

   Note:

   The gateway converts both ENode FIP FLOGI and FIP FDISC messages into FC FDISC messages, because the gateway has already performed FC FLOGI with the FC switch, so all subsequent connection requests on the gateway NP_Port are FDISC requests for virtual (NPIV) connections. FDISC messages request a virtual N_Port connection over an existing physical N_Port connection.

3. The FC switch processes the request, accepts it, assigns a unique FCID for the connection, and then sends the response to the gateway. If the FC switch rejects the FDISC request, no virtual link is established.

4. The gateway maps the FC switch response to the ENode VN_Port, converts the FC acceptance message to a FIP FLOGI or FIP FDISC response, and sends it to the ENode VN_Port.

5. The ENode VN_Port accepts the FCID, and the virtual link is established.

If an ENode sends an FDISC, the proxy gateway switch checks whether the ENode has already performed a FLOGI to create the initial connection. If the ENode has not performed a FLOGI, the FDISC request is dropped.

The FC protocol does not recognize multipoint-to-point connections. Although the gateway can aggregate traffic from multiple FCoE servers on one NP_Port, each virtual link appears to be an individual point-to-point link between an FCoE ENode VN_Port and the FC switch, not as an aggregated multipoint-to-point link. The gateway is essentially invisible to the FC protocol, so the virtual link looks and acts like a point-to-point link from the FCoE device to the FC switch.

Proxy FIP Maintenance

The gateway sends and receives periodic FIP keepalive messages to and from ENode VN_Ports to maintain the connection between the gateway and the ENodes.

Proxy FIP Logout

As with FIP discovery and FIP FLOGI, the gateway represents the FCoE device in transactions with the FC switch and represents the FC switch in transactions with the FCoE device:

1. An ENode VN_Port sends a FIP LOGO message to log off and terminate the virtual link connection.

2. The gateway converts the FIP LOGO to an FC LOGO and relays it to the FC switch.

3. The FC switch responds to the LOGO request.

4. The gateway converts the FC LOGO response to a FIP LOGO response and relays it to the VN_Port, completing the logout and terminating the virtual link.