HP StorageWorks 8/8 HP StorageWorks Fabric OS 6.2 administrator guide (5697-00 - Page 286

redundancy. If a link goes down, part of the fabric becomes isolated. FSPF ensures that the topology is loop free and that the frame is never forwarded over the same ISL more than once. FSPF calculates paths based on the destination domain ID. The fabric protocol must complete domain ID assignments before routing can begin. ISLs provide the physical pathway when the Source ID (SID) address has a frame destined to a port on a remote switch Destination ID (DID). When an ISL is attached or removed from a switch, the FSPF updates the route tables to reflect the addition or deletion of the new routes. As each host transmits a frame to the switch, the switch reads the SID and DID in the frame header. If the domain ID of the destination address is the same as the switch (intra-switch communications), the frame buffer is copied to the destination port and a credit R_RDY is sent to the host. The switch needs to read only word 0 and word 1 of the Fibre Channel frame to perform what is known as cut-through routing. A frame may begin to emerge from the output port before it has been entirely received by the input port. The entire frame does not need to be buffered in the switch. If the destination domain ID is different than the source domain ID, the switch consults the FSPF route table to identify which local E_Port provides the Fabric Shortest Path First to the remote domain. Routing policies By default, all routing protocols place their routes into a routing table. You can control the routes that a protocol places into each table and the routes from that table that the protocol advertises by defining one or more routing policies and then applying them to the specific routing protocol. The routing policy is responsible for selecting a route based on one of two user-selected routing policies: • Port-based routing • Exchange-based routing Routing is handled by the FSPF protocol and uses only the port-based routing policy on the following switches: • HP StorageWorks SAN Switch 2/8-EL • HP StorageWorks SAN Switch 2/8V • HP StorageWorks SAN Switch 2/16V • HP StorageWorks SAN Switch 2/32 • HP StorageWorks Core Switch 2/64 • HP StorageWorks SAN Switch 2/16, 2/16-EL, 2/16N • HP StorageWorks MSA SAN Switch 2/8 • HP StorageWorks SAN Director 2/128 (all 2 Gb/s ASICs) Routing is handled by the FSPF protocol and either the port-pased routing or exchange-based routing policies on the following switches: • HP StorageWorks 4/8 and 4/16 SAN Switches • HP StorageWorks 8/8 and 8/24 SAN Switches • HP StorageWorks SAN Switch 4/32 • HP StorageWorks 4/64 SAN Switch • HP StorageWorks SAN Switch 4/32B • HP StorageWorks 8/40 SAN Switch • HP StorageWorks 8/80 SAN Switch • HP StorageWorks 400 Multi-Protocol Router • HP StorageWorks 4/256 SAN Director • HP StorageWorks DC SAN Backbone Director • HP StorageWorks DC04 SAN Director Switch enterprise-class platforms (all 4 Gb/s ASICs and later) Each switch can have its own routing policy and different policies can exist in the same fabric. 284 Routing traffic