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

478 Fabric OS Administrator’s Guide
53-1002148-02
FC Router port cost configuration
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The router port cost feature optimizes the usage of the router port links by directing the traffic to a
link with a smaller cost.
Every IFL has a default cost. The default router port cost values are:
• 1000 for legacy (v5.1 or XPath FCR) IFL
• 1000 for EX_Port IFL
• 10,000 for VEX_Port IFL
The FCR router port cost settings are 0, 1000, 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.
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 from the edge fabric to
display these link costs.
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 IFLs to a separate port group (for example ports 0–
7) than the higher router cost IFLs (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.
Source EX_Ports can balance loads across multiple destination EX_Ports attached to the same
edge fabric using exchange IDs from the routed frames as keys to distribute the traffic.