Dell PowerSwitch S5212F-ON EMC SmartFabric OS10 User Guide Release 10.5.1 - Page 348

Po 10 Eth 1/1/9 Up Multiswitch fabric (E Port) E Ports are interfaces that connect the FC switches to form a multiswitch SAN fabric. These ports carry control frames between the switches to configure and maintain the fabric. An Inter-Switch Link (ISL) is created when you connect two E Ports to one another. FC ISL maintains the information in FC frames as the traffic flows between multiple switches. The multiswitch configuration sets the port mode as E. The switch port initialization for an E Port includes the exchange of Exchange link parameters (ELP) message sequences, on the ISL between two E Ports. Use the multiswitch option to enable the multiswitch fabric mode. In the multiswitch fabric mode, the default port mode is F. You can enable the E Port mode by configuring the port mode as E. When the E port becomes operationally up, the link initialization starts, which include the exchange of link parameters (ELP) with the peer switch through the ISL. On successful exchange of ELP, the switches are allowed to participate in principal switch election. Delete multiswitch configurations when disabling a feature. You can disable the multiswitch mode only if you delete the related configurations. Principal switch selection A principal switch is a switch that assigns and maintains a unique domain ID across the fabric. During the principal switch selection, the switch with the highest priority becomes the principal switch. If two switches have the same priority, the switch with lower WWN becomes the principal switch. The valid range to set the priority is 1, and from 3 to 255. Priority 1 has the highest priority. A switch with priority 255 cannot become the principal switch. You can modify the switch priority only when the vfabric is in inactive state. You can activate the vfabric only by adding VLAN and fcmap configuration under the vfabric configuration view. Ensure to configure the switch priority before activating the vfabric. An ISL that points towards the principal switch is called an upstream principal ISL, which is discovered during principal switch election. After completing the fabric reconfiguration, the local switch requests for domain ID allocation through an upstream principal ISL. An ISL that points away from the principal switch is called a downstream principal ISL. Link failure results in rebuilding the fabric. When the principal ISL fails and if no other path exists between the two affected switches, then the build fabric (BF) operation is triggered. If the backup link (nonprincipal ISL) is available, then the link failure recovery is triggered. Whenever the principal switch election is retriggered nondisruptively, the switches check if the previously assigned domain IDs match the newly elected principal switch. The switches remember the previously assigned domain IDs. If you have already configured the preferred domain IDs, during a switch reboot, the switches check for the preferred domain IDs. If you do not configure a preferred domain ID, the previously assigned domain ID is considered throughout the switch reload. When two different fabrics join and when both fabrics have the same domain ID configured, the reconfigure fabric (RCF) operation occurs as the domain ID overlaps. Any duplicate domain IDs assigned during a fabric merge are detected during the EFP exchange. Fabric reconfigurations occur in two ways. They are nondisruptive reconfiguration (build fabric) and disruptive reconfiguration (reconfigure fabric). BF occurs when two configured fabrics merge and both the fabrics have nonoverlapping domain ID list. Reconfigure fabric occurs when both the fabrics have overlapping domain ID list, which can be detected through EFP exchange. Login request packets from F or VF ports are not served until the domain ID allocation is successfully completed. The principal switch assigns a requested domain ID based on the availability of the ID. The FLOGI requests, received until the domain ID is assigned are silently dropped. All the switches in the fabric must have identical E_D_TOV ranging between 1000 ms to 10,000 ms and R_A_TOV timer values ranging between 5000 ms and 10000 ms respectively. If there is a mismatch in the configuration value, that switch is isolated from the fabric. Fabric shortest path first (FSPF) FSPF is a link state path selection protocol. All the ISL links between FC switches are treated as point to point. FSPF tracks the state of the links on all switches in the fabric, and associates a cost with each link. FSPF computes paths from one switch to all other switches present in the fabric. FSPF computes the best path by adding the cost of the link that is traversed by the paths and by choosing the least path with the least cost to reach a particular domain ID from a switch. It also computes the best path between the switches that is based on the link cost. FSPF computes the shortest path from the local domain to all other domains available in the fabric and updates route details with the next hop to reach the shortest path. Hold-time interval must be elapsed between the two runs of shortest path first (SPF) run. This release of OS10 does not support incremental SPF run. E ports exchange FSPF hello packets periodically on the ISL to form and maintain neighbor adjacency. The FSPF link state updates (LSU) use this link adjacency to exchange the link state information of a switch, across the fabric. Each switch maintains a link state database that is based on this link state information. This link state database is used in the SPF (Dijkstra algorithm) to 348 Fibre Channel