Dell Brocade G620 Brocade 8.0.1 Fabric OS Administratiors Guide - Page 512

Using FC-FC Routing to Connect Fabrics 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. 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. Setting router port cost for an EX_Port The router port cost value for an EX_Port is set automatically when the EX_Port is created. You can modify the cost for that port to force a path to have a higher or lower cost. You can configure the EX_Port or VEX_Port with values of either 1,000 or 10,000. For example, if you want to differentiate between two EX_Port links with different speeds, you can assign 1,000 to one link and 10,000 to the other link. Brocade Fabric OS Administration Guide, 8.0.1 512 53-1004111-02