Understanding FIP Parameters on an FCoE-FC Gateway
By default, FIP is enabled, and the default FIP settings are valid on all FCoE interfaces that are part of the gateway FC fabric. You can configure some FIP parameters at a global level or on a specific interface. Some FIP parameters can be configured only at the global level or only at the individual interface level. When you configure a parameter at the interface level, the configuration overrides the global setting for that interface only.
FIP Keepalive Advertisement Period
The FIP keepalive advertisement period (fka-adv-period) is the time interval between messages that verify the connection is still valid and the device at the other end of the virtual link is still reachable. The ENode sends an ENode FIP keepalive advertisement to the gateway with the ENode MAC address as the source address to verify its reachability. The ENode also sends VN_Port FIP keepalive messages for every VN_Port on the ENode that is logged in to the gateway, with the VN_Port MAC address as the source address.
The FIP keepalive advertisement period also determines the time interval between unsolicited multicast discovery advertisements from the gateway to the ALL-ENode-MACs multicast address. Unsolicited multicast discovery advertisements serve as keepalive messages from the gateway to the ENodes and also advertise the gateway’s presence on the network.
The gateway sends the periodic unsolicited multicast discovery advertisements to the ENodes. On the gateway, you can configure a global FIP keepalive advertisement period for an FC fabric and you can configure a FIP keepalive advertisement period for individual interfaces to override the global setting.
Addressing Mode
For FIP transactions, the ENode identifies itself using the globally unique MAC address assigned to the CNA by the manufacturer. After FIP has established a virtual link between an ENode VN_Port and the gateway, for FCoE transactions, the VN_Port identifies itself using a locally unique MAC address. The format of the locally unique MAC address depends on the addressing mode the fabric supports and the addressing mode the ENode is programmed to use.
The addressing mode is not a configurable parameter on the gateway. FC fabrics on the gateway support only the fabric provided MAC address (FPMA) addressing mode for FCoE transactions. The gateway does not support the server provided MAC address (SPMA) addressing mode. ENodes that use SPMA cannot log in to the gateway.
The FC switch assigns a locally unique FPMA to an ENode MAC through the FLOGI or FDISC process:
During the FIP discovery process, the ENode compiles a list of compatible FCFs (including the gateway) in the fabric. A compatible addressing mode is one of the criteria an FCF must meet to be added to an ENode’s compatible FCFs list.
The ENode MAC transmits a FLOGI or FDISC to the FCF that includes the addressing modes the ENode supports.
If the FCF supports an addressing mode the ENode uses, the FCF accepts the FLOGI or FDISC and assigns the FPMA in the accept message (FIP FLOGI LS_ACC or FIP NPIV FDISC LS_ACC). If the ENode uses an addressing mode that is incompatible with the FCF, the FLOGI or FDISC is rejected.
The FPMA uniquely identifies a single VN_Port at that ENode MAC in FCoE transactions with the FCF. Each VN_Port connection receives its own unique FPMA to identify its virtual link connection. When an ENode uses NPIV to create multiple VN_Ports, each VN_Port virtual link receives its own unique FPMA to identify its traffic.
An FPMA consists of two concatenated 24-bit values:
The upper 24 bits are the FCF’s FC-MAP value, which is a MAC address prefix that is unique to the fabric.
The lower 24 bits are the locally unique FCID that the FCF (FC switch) assigns to the VN_Port.
The combination of these values guarantees that each FPMA is unique within a fabric.
FC-MAP
The FCoE mapped address prefix (FC-MAP) value is a MAC address prefix used by the FCF that is unique within a given fabric. The FCF uses the FC-MAP for FCoE traffic within that fabric. The FCF rejects FCoE traffic that uses an FC-MAP value that does not match the FCF’s FC-MAP value. In most cases, the FCF uses the default FC-MAP value (0EFC00), but a pool of 256 values is available (0EFC00 through 0EFCFF).
The gateway learns FC switches in the fabric that match the gateway fabric’s FC-MAP value. To learn and communicate with an FC switch, the FC-MAP value for a fabric (or for the fabric’s FCoE VLAN) on the gateway must match the FC switch’s FC-MAP value. If the FC-MAP values do not match, no connection is established.
Changing the FC-MAP value causes all logins to drop and forces the ENodes to log in again.
FCoE Trusted Fabric
By default, all interfaces are untrusted interfaces. You can globally configure all of the ports in a specified gateway FC fabric to be FCoE trusted. This reduces system overhead by eliminating the need for filters. The total number of FCoE sessions (ENode to FCF sessions) the system can support is 2500 sessions. Sessions are defined as the combined number of VN_Port to VF_Port sessions and VN_Port to VN_Port sessions. (Although VN2VF and VN2VN sessions run in different FCoE VLANs, the session limit is a system limit, not a per-VLAN limit.)
A session is a FLOGI or FDISC login to the FC SAN fabric. Session does not refer to end-to-end server-to-storage sessions. There is no limit to the number of end-to-end server-to-storage sessions.
Changing the fabric ports from untrusted to trusted removes any existing FIP snooping filters from the ports and terminates the existing sessions. Changing the fabric ports from trusted to untrusted forces all of the FCoE sessions on those ports to log out so that when the ENodes and VN_Ports log in again, the switch can build the appropriate FIP snooping filters.
Maximum Number of FCoE Sessions Per ENode
You can configure the maximum number of FCoE session logins from each ENode that are permitted on the gateway FC fabric. The number of sessions is the ENode FLOGI session plus the VN_Port FDISC sessions on that ENode. Regardless of whether the fabric is trusted or untrusted, the maximum number of FCoE sessions per ENode is 2500 sessions. The total number of sessions cannot exceed the gateway fabric’s maximum limit of 2500 sessions.
The maximum number of FCoE sessions per ENode is a global configuration for all members of the gateway FC fabric and cannot be configured on a per-interface basis.
Session does not refer to end-to-end server-to-storage sessions. There is no limit to the number of end-to-end server-to-storage sessions.
Priority
When the FIP discovery process offers an ENode the choice of more than one FCF-MAC on a given FCF to use for login, the ENode chooses the FCF-MAC to which to send a login request based on the FCF-MAC priority. The lower the priority number, the higher the FCF-MAC’s priority. The ENode selects the highest-priority (lowest priority number) FCF-MAC for the login request.
An ENode can receive multiple FCF-MAC advertisements from the same FCF in two ways:
During the FIP discovery process, an FCF can receive an ENode MAC’s multicast discovery solicitation on multiple FCF-MACs. Each FCF-MAC replies with a unicast discovery advertisement to the ENode. The ENode determines that the advertisements are from the same FCF, because the value in the Name_Identifier descriptor is the same in each advertisement.
During the FIP discovery process, an ENode MAC can receive unsolicited multicast discovery advertisements from multiple FCF-MACs on the same FCF. The ENode determines that the advertisements are from the same FCF, because the value in the Name_Identifier descriptor is the same in each advertisement.
On the gateway, you can configure the priority value for an entire fabric or for an individual interface. The default value for both the fabric and the individual interfaces is 128 (the highest priority is 0; the lowest priority is 255).