Dell PowerConnect Brocade 300 Fabric OS Administrator's Guide v7.1.0 - Page 51

Device login 1 Device login A device can be storage, a host, or a switch. When new devices are introduced into the fabric, they must be powered on and, if a host or storage device, connected to a switch. Switch-to-switch logins (using the E_Port) are handled differently than storage and host logins. E_Ports exchange different frames than the ones listed below with the Fabric Controller to access the fabric. Once storage and host devices are powered on and connected, the following logins occur: 1. FLOGI-Fabric Login command establishes a 24-bit address for the device logging in, and establishes buffer-to-buffer credits and the class of service supported. 2. PLOGI-Port Login command logs the device into the name server to register its information and query for devices that share its zone. During the PLOGI process, information is exchanged between the new device and the fabric. Some of the following types of information exchanges occur: • SCR-State Change Registration registers the device for State Change Notifications. If a change in the fabric occurs, such as a zoning change or a change in the state of a device to which this device has access, the device receives a Registered State Change Notification (RSCN). • Registration-A device exchanges registration information with the name server. • Query-Devices query the name server for information about the device it can access. Principal switch In a fabric with multiple switches, and one inter-switch link (ISL) exists between any two switches, a principal switch is automatically elected. The principal switch provides the following capabilities: • Maintains time for the entire fabric. Subordinate switches synchronize their time with the principal switch. Changes to the clock server value on the principal switch are propagated to all switches in the fabric. • Manages domain ID assignment within the fabric. If a switch requests a domain ID that has been used before, the principal switch grants the same domain ID unless it is in use by another switch. 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 principal switch to establish that the new switch is an E_Port and that it has information to exchange. If everything is acceptable to the principal 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 principal 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 principal switch and the new switch sends an Exchange Fabric Parameters (EFP) frame to the principal switch, requesting principal switch priority and the domain ID list. Buffer-to-buffer credits for the device and switch ports are exchanged in the SW_ACC command sent to the device in response to the FLOGI. Fabric OS Administrator's Guide 51 53-1002745-02