Fc Router Port Cost Configuration; Port Cost Considerations - HP A7533A - Brocade 4Gb SAN Switch Base Administrator's Manual

FC Router port cost configuration

The router port cost is set automatically. This section provides information about the router port cost and
describes how you can modify the cost for a port if you want to change the default value.
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 1000 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 lower than the others, 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.
The router port cost feature optimizes the usage of the router port links by directing the traffic to a link with
a smaller cost. For example, if there are EX_ and VEX_Port connections to the same edge fabric, the traffic
will be directed through the EX_Port link.
Every IFL has a default cost. The default router port cost values are:
• 1000 for legacy (5.1 or XPath FCR) IFL
• 1000 for EX_Port IFL
• 10,000 for VEX_Port IFL
The FCR 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.
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
More than two router port sets can exist in an HP StorageWorks 4/256 SAN Director, HP
StorageWorks DC SAN Backbone Director, or HP StorageWorks DC04 SAN Director Switch with two
B-Series Multi-Protocol Router Blades.
• 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 VEX_Port and a high-speed EX_Port 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 flows 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.
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