HP StorageWorks 1606 Brocade Fabric OS Administrator's Guide v6.3.0 (53-100133 - Page 104

4 Routing policies 3: Exchange Based Routing Policy 0: AP Shared Link Policy 1: AP Dedicated Link Policy Exchange-based routing The choice of routing path is based on the Source ID (SID), Destination ID (DID), and Fibre Channel originator exchange ID (OXID), optimizing path utilization for the best performance. Thus, every exchange can take a different path through the fabric. Exchange-based routing requires the use of the Dynamic Load Sharing (DLS) feature; when this policy is in effect, you cannot disable the DLS feature. Exchange-based routing is also known as Dynamic Path Selection (DPS). DPS is where exchanges or communication between end-devices in a fabric are assigned to egress ports in ratios proportional to the potential bandwidth of the ISL or trunk group. When there are multiple paths to a destination, the input traffic will be distributed across the different paths in proportion to the bandwidth available on each of the paths. This improves utilization of the available paths, thus reducing possible congestion on the paths. Every time there is a change in the network (which changes the available paths), the input traffic can be redistributed across the available paths. This is a very easy and non-disruptive process when the exchange-based routing policy is engaged. Port-based routing The choice of routing path is based only on the incoming port and the destination domain. To optimize port-based routing, DLS can be enabled to balance the load across the available output ports within a domain. Using port-based routing, you can assign a static route, in which the path chosen for traffic does not change when a topology change occurs unless the path becomes unavailable. If the static route violates FSPF, it is not used. In contrast, exchange-based routing policies always employ dynamic path selection. NOTE For FC routers only: When an FC router is in port-based routing mode, the backbone traffic is load-balanced based on SID and DID. When an FC router is in exchange-based routing mode, the backbone traffic is load-balanced based on SID, DID, and OXID. Whatever routing policy a switch is using applies to the VE_Ports as well. For more information on VE_Ports, refer to the Fibre Channel over IP Administrator's Guide. AP route policy On the Brocade 7500 switch and FR4-18i blade, there are eight internal physical links used by EX_ and VEX_Port functionality. The links are shared by both ingress and egress traffic on EX_ and VEX_Ports. The AP (appliance) route policy dedicates some links for ingress traffic and some links for egress traffic. The AP Dedicated Link Policy relieves internal congestion in an environment where: • There is a large amount of traffic going through both directions at the same time. • There is a reduction of the effect of slow devices on the overall switch performance. 62 Fabric OS Administrator's Guide 53-1001336-01