Users Guide

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
compute the shortest path to reach a switch in the fabric. The name server service uses these routes to synchronize the name
server database across the fabric. Hence, FSPF helps in building the fabric connectivity. Configure the same hold-time value on
all the switches to ensure a consistent route convergence, and to avoid intermittent forwarding loop. When you configure a
shorter hold-time, the route update is faster. FSPF detects the link failures in the fabric and recomputes the next available
shortest path to reach the destination domain. FSPF also updates the change in route such as addition of new link or removal of
existing link and when the link goes up or down.
Distributed domain name server (DNS)
DNS is responsible for name server registration and management of Nx_Ports that are attached to the switch. The registered
name entries are stored in the local database. Each switch exchanges its name server information with other switches in the
fabric to maintain a synchronized and distributed name service.
Each switch in the fabric must distribute switch registered state change notification (SW_RSCNs) throughout the fabric
whenever there is a change in its local database.
Topology changes trigger SW_RSCN, and NS queries. Each switch forwards the SW_RSCN packets on the FSPF computed
path towards the other switches in the fabric.
System logs
The system log file contains the system logs for the following events:
● FC port operationally up
● Principal switch selection
● Domain ID assignment
● Port isolation
● Fabric or nondisruptive reconfiguration data
● Disruptive fabric reconstruction
● Error conditions when ELP or EFP exchange fails, and when the port goes into isolated state
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Fibre Channel