Brocade Fabric OS Administrators Guide (Supporting Fabric OS v7.3.0) User Manual
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fabric. This feature is useful when an FC router has multiple connections to the source edge fabric, and
the backbone fabric has multiple FC routers connected through FCIP links (VE_Ports) and FC links
(E_Ports). The selection of a low cost path depends on individual ISL link cost settings in the backbone
fabric. Traffic originating from a domain in an edge fabric can choose any equal cost path in order to
reach the destination edge fabric. This traffic can be transmitted through high cost paths, such as FCIP
links, within the backbone fabric even though low cost paths, such as FC links, are present.
When the shortest IFL mode is enabled, each FC router calculates the shortest path for each of its
locally-connected source edge fabrics to a remote destination edge fabric that is connected to another
FCR in the same backbone fabric. The FC router performs this calculation by identifying all paths in the
backbone fabric that can connect the source edge fabric to the destination edge fabric. The cumulative
ISL link cost for each path is then calculated:
• For any path for which the cumulative ISL link cost of the path is greater than or equal to 10,000, the
FC router sets the link cost from the front domain to translate the domain as 10,001.
• For any path for which the cumulative ISL link cost of the path is less than 10,000, the link cost from
front domain to translate domain will remain at 10,000, which is the shortest IFL path.
NOTE
The shortest IFL solution is applicable only when the edge fabric has multiple FC router connections
and the backbone fabric has at least one available low cost path. Shortest IFL mode should be enabled
on all FC routers in the backbone fabric for this feature to work correctly.
shows a shortest IFL solution. In order for Host 12 in Domain 1 in Edge fabric 1 to reach
Target 2 in Domain 3 in Edge fabric 3, traffic can choose one of two paths in the backbone fabric:
• Path 1: Edge fabric 1-FCR1 - FCR2 -FCR3 -Edge fabric 3.
• Path 2: Edge fabric 1-FCR4 - FCR3 -Edge fabric 3.
The second path is identified as the low cost path by setting the ISL link cost to 5,000. The first path is
considered the high cost path where the cumulative ISL cost is 10,000.
NOTE
Link cost should be set in the direction of traffic flow from the source edge fabric to the destination edge
fabric.
Using FC-FC Routing to Connect Fabrics
Fabric OS Administrators Guide
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