External routes are propagated through an OSPF area as a type 5 from an ASBR,  or type 7 LSA from an ASBR in an NSSA. These routes from outside the OSPF domain are can either be E1 or E2 routes and they are treated in slightly different ways.

E1 or External Type Routes - The cost of E1 routes is the cost of the external metric with the additional of the internal cost within OSPF to reach that network.

E2 or External Type2 Routes – The cost of E2 routes will always be the external metric, the metric will takes no notice of the internal cost to reach that network.

If 2 external type 2 routes exist with the same metric to the same destination the route with the lowest metric to the ASBR will be used. Also if an E1 and and E2 route exist to the same destination the E1 route will always be preferred irrespective of the metric.

Cisco’s excellent reference on the topic is http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml#t33

Off Topic – The weather in the UK for some reason is always exceptional as its an island nation. For the last 5 or so days we have had an exception heatwave and it has been 30°C+ which were just not used to, and I have been surprised how much it has affected my ability to study, I just haven’t been able to concentrate for anywhere near as long as I can in the cold.