Fabric OS Administrator's Guide v7.0.0 (53-1002148-02, June 2011)

Fabric OS Administrator’s Guide 73
53-1002148-02
Routing policies
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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 is 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.
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
Two additional AP policies are supported under exchange-based routing:
• AP Shared Link policy (default)
• AP Dedicated Link policy
The AP policies are independent of the routing policies. Every routing policy supports both AP
policies.
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.
It is recommended that the default AP Shared Link policy be used for most environments. Also, it is
recommended that you design a SAN that localizes host-to-target traffic by reducing the amount of
traffic through the router.
ATTENTION
Setting either AP route policy is a disruptive process.
Routing in Virtual Fabrics
Virtual Fabrics support DPS on all partitions. DPS is limited where multiple paths are available for a
logical fabric frame entering a Virtual Fabrics chassis from a base fabric that is sent out using one
of the dedicated ISLs in a logical switch.