Brocade Fabric OS Administrators Guide (Supporting Fabric OS v7.3.0) - Manual (Page 553)

FC router port cost configuration
FC routers optimize the usage of the router port links by directing traffic to the link with the smallest
router port cost.
The FC router port cost is similar to the link cost setting available on E_Ports, which allows you to
customize traffic flow. The router port link cost values are either 0, 1,000, or 10,000. The router module
chooses the router port path based on the lowest cost for each FID connection. If multiple paths exist
where one path costs less than the others, then the lowest cost path is used. If exchange-based routing
has not been disabled and multiple paths exist with the same lowest cost, there will be load sharing
over these paths.
Every IFL has a default cost. The default router port cost values are as follows:
• 1,000 for a legacy (v5.1 or XPath FCR) IFL
• 1,000 for an EX_Port IFL
• 10,000 for a VEX_Port IFL
The FC router port cost settings are 0, 1,000, or 10,000. If the cost is set to 0, the default cost will be
used for that IFL. The FC router port cost is persistent and is saved in the existing port configuration file.
FC router port cost is passed to other routers in the same backbone. Link costs from the front domain to
the translate (xlate) domain remain at 10,000. You can use the lsDbShow command from the edge
fabric to display these link costs.
The FC router port cost is set automatically. You can modify the cost for a port if you want to change the
default value.
Port cost considerations
The router port cost has the following considerations:
• Router port sets are defined as follows:
‐ 0-7 and FCIP Tunnel 16-23
‐ 8-15 and FCIP Tunnel 24-31
• The router port cost does not help distinguish one IFL (or EX_ and VEX_Port link) from another, if all
the IFLs are connected to the same port set. Therefore, if you connect IFL1 and IFL2 to the same
edge fabric in port set 0-7 and then configure them to different router port costs, traffic is still
balanced across all the IFLs in the same port set.
• Use proper SAN design guidelines to connect the IFLs to different port sets for effective router port
cost use. For example, if both a low-speed IFL and a high-speed IFL are going to the same edge
fabric, connect the lower router cost IFL to a separate port group (for example, ports 0-7) than the
higher router cost IFL (for example, ports 8-15). For VEX_Ports, you would use ports in the range of
16-23 or 24-31.
You can connect multiple EX_Ports or VEX_Ports to the same edge fabric. The EX_Ports can all be on
the same FC router, or they can be on multiple routers. Multiple EX_Ports create multiple paths for
frame routing. Multiple paths can be used in two different, but compatible, ways:
• Failing over from one path to another.
• Using multiple paths in parallel to increase effective data transmission rates.
EX_Ports and VEX_Ports, when connected, are assigned different router port costs and traffic will flow
only through the EX_Ports. Routing failover is automatic, but it can result in frames arriving out of order
when frames take different routes. The FC router can force in-order delivery, although frame delivery is
delayed immediately after the path failover.
FC router port cost configuration
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