Current network infrastructures exhibit poor power efficiency, running network devices at full capacity all the time regardless of the traffic demand and distribution over the network. Most research on router power management are at component level or link level, treating routers as isolated devices. A complementary approach is to facilitate power management at network level by routing traffic through different paths to adjust the workload on individual routers or links. Given the high path redundancy and low link utilization in today's large networks, this approach can potentially allow more network devices or components to go into power saving mode. This paper proposes an intra-domain traffic engineering mechanism, GreenTE, which maximizes the number of links that can be put into sleep under given performance constraints such as link utilization and packet delay. Using network topologies and traffic data from several wide-area networks, our evaluation shows that GreenTE can reduce line-cards' power consumption by 27% to 42% under constraints that the maximum link utilization is below 50% and the network diameter remains the same as in shortest path routing.