For OSPF, the best path to a destination is the path that offers the least-cost metric (least-cost delay). You can configure OSPF cost metrics to specify preferred paths. You can configure metric speed globally or for specific ports and interfaces on the network. In addition, you can control redistribution options between nonOSPF interfaces and OSPF interfaces.
Assign default metric speeds for different port types, such as 10 Mb/s or 1 Mb/s ports. You can specify a new metric speed for an IP interface. An IP interface can be a brouter port or a VLAN.
RFC1583 states the following:
"OSPF supports two types of external metrics. Type 1 external metrics are equivalent to the link state metric. Type 2 external metrics are greater than the cost of path internal to the Autonomous System. Use of Type 2 external metrics assumes that routing between Autonomous Systems is the major cost of routing a packet, and eliminates the need for conversion of external costs to internal link state metrics."
"Both Type 1 and Type 2 external metrics can be present in the Autonomous System at the same time. In that event, Type 1 external metrics always take precedence."