Dell Brocade G620 Brocade 8.0.1 Fabric OS Administratiors Guide - Page 33

Understanding Fibre Channel Services E_Port login process An E_Port does not use a FLOGI to log in to another switch. Instead, the new switch exchanges frames with the neighboring switch to establish that the new switch is an E_Port and that it has information to exchange. If everything is acceptable to the neighboring switch, it replies to the new switch with an SW_ACC (accept) frame. The initializing frame is an Exchange Link Parameters (ELP) frame that allows an exchange of parameters between two ports, such as flow control, buffer-to-buffer credits, RA_TOV, and ED_TOV. This is not a negotiation. If one or the other port's link parameters do not match, a link does not occur. Once an SW_ACC frame is received from the neighboring switch, the new switch sends an Exchange Switch Capabilities (ESC) frame. The two switches exchange routing protocols and agree on a common routing protocol. An SW_ACC frame is received from the neighboring switch and the new switch sends an Exchange Fabric Parameters (EFP) frame to the neighboring switch, requesting principal switch priority and the domain ID list. Buffer-tobuffer credits for the device and switch ports are exchanged in the SW_ACC command sent to the device in response to the FLOGI. Fabric login process A device performs a fabric login (FLOGI) to determine if a fabric is present. If a fabric is detected then it exchanges service parameters with the fabric controller. A successful FLOGI sends back the 24-bit address for the device in the fabric. The device must issue and successfully complete a FLOGI command before communicating with other devices in the fabric. Because the device does not know its 24-bit address until after the FLOGI, the source ID (SID) in the frame header of the FLOGI request are zeros (0x000000). Port login process The steps in the port initialization process occur as the result of a protocol that functions to discover the type of device connected and establish the port type and negotiate port speed. See Port Types on page 73 for a discussion of available port types. The Fibre Channel protocol (FCP) auto discovery process enables private storage devices that accept the process login (PRLI) to communicate in a fabric. If device probing is enabled, the embedded port performs a PLOGI and attempts a PRLI into the device to retrieve information to enter into the name server. This enables private devices that do not explicitly register with the Name Server (NS) to be entered in the NS and receive full fabric access. A fabric-capable device registers its information with the name server during a FLOGI. These devices typically register information with the name server before querying for a device list. The embedded port still performs a PLOGI and attempts a PRLI with these devices. If a port decides to end the current session, it initiates a logout. A logout concludes the session and terminates any work in progress associated with that session. To display the contents of a switch's name server, use the nsShow or nsAllShow command. For more information about these commands, refer to the Fabric OS Command Reference. RSCNs A Registered State Change Notification (RSCN) is a notification frame that is sent to devices that are zoned together and are registered to receive a State Change Notification (SCN). The RSCN is responsible for notifying all devices of fabric changes. The following general list of actions can cause an RSCN to be sent through your fabric: ∙ A new device has been added to the fabric. ∙ An existing device has been removed from the fabric. ∙ A zone has changed. ∙ A switch name has changed or an IP address has changed. Brocade Fabric OS Administration Guide, 8.0.1 53-1004111-02 33