Users Guide

124 Fabric OS Administrator’s Guide
53-1002920-02
Routing policies
4
Dynamic Path Selection
DPS assigns communication paths between end devices in a fabric to egress ports in ratios
proportional to the potential bandwidth of the ISL, ICL, 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.
AP route policies
Two additional AP policies are supported under exchange-based routing:
• AP Shared Link policy (default)
• AP Dedicated Link policy
NOTE
AP policies are independent of routing policies. Every routing policy supports both AP policies.
The AP Dedicated Link policy relieves internal congestion in an environment in which:
• 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 (VF) supports 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.
The AP policy affecting the DPS behavior, whether it is exchange-based, device-based, or
port-based, is configured on a per-logical switch basis. In-order delivery (IOD) and DLS settings are
set per logical switch as well. IOD and DLS settings for the base switch affect all traffic going over
the base fabric including any logical fabric traffic that uses the base fabric.
CAUTION
Setting the routing policy is disruptive to the fabric because it requires that you disable the switch
where the routing policy is being changed.