Reference Guide

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 Fabric OS
FCIP Administrator's Guide .
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). For more information on DPS refer to Dynamic Path Selection
on page 115.
Device-based routing
Device-based routing optimizes routing path selection and utilization based on the Source ID (SID) and Destination ID (DID) of the path
source and destination ports. As a result, every distinct flow in the fabric can take a different path through the fabric. Effectively, device-
based routing works the same as exchange-based routing but does not use the OXID field. This helps to ensure that the exchanges
between a pair of devices stay in order.
NOTE
Device-based routing requires the use of Dynamic Load Sharing (DLS); when this policy is in effect, you cannot disable the
DLS feature.
Device-based routing is also a form of Dynamic Path Selection (DPS). For more information on DPS refer to Dynamic Path Selection on
page 115.
NOTE
Device-based routing is supported in FICON environments, and in open environments only when FICON coexists.
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.
Displaying a dynamic path selection group for reachable domains
You can use the portChannelShow command to display a dynamic path selection group for one or all reachable domains.
∙ Use the portChannelShow command to display the port channels from a domain to all the reachable domains on the switch.
For example,
switch:admin> /fabos/cliexec/portchannelshow
6 domain(s) in the fabric; Local Domain ID: 4
Routing Traffic
Brocade Fabric OS Administration Guide, 8.0.1
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