Modern data center networks provide multiple paths between host pairs to guarantee high aggregated network bandwidth and transmission reliability. However, data center networks suffer from various uncertainties such as highly dynamic traffic and heterogeneous devices. These uncertainties easily lead to network asymmetry and cause significant packet reordering. Unfortunately, due to lacking the explicit reordering feedback, existing sender-based and receiver-based solutions hardly adapt to asymmetric data center networks and cause long-tailed flow completion time as well as throughput loss. In this paper, we propose a per-packet transmission scheme RMC to eliminate the impact of packet reordering and handle uncertainties in asymmetric networks. To avoid unnecessary fast retransmission, the switch proactively identifies packet reordering according to local queue length and global path latency. Furthermore, we employ a coding technique to reduce long-tailed flow completion time under network asymmetry. Through a series of large-scale NS2 simulations and testbed experiments, we demonstrate that RMC reduces flow completion time by up to 72% compared with existing protocols.