防火牆是現今網路中的重要設備，負責區隔內部網路和公共網路，維護內部網路安全。然而防火牆也存在幾個重要的問題，首先，防火牆的規則是由網管人員設定，近年來隨著網路科技蓬勃發展、虛擬技術大量應用，此項工作已帶給網管人員龐大的負擔。其次，防火牆雖可隔離外部網路，阻擋有害流量，但對內部網路的防範卻毫無用武之地。目前市面上普遍使用入侵偵測系統(IDS)進行偵測，但僅能在發現攻擊行為後發出警告訊息，無法即時處理。最後，企業在連外網路部分，通常採用多條線路進行備援，並倚賴多路頻寬負載平衡器(Multi-WAN load balancer)增加頻寬的使用率，但在線路數量上卻受限於廠商所制定之規格，無法彈性調整。而在負載平衡演算法方面，也只能基於網路特徵(IP位置)、權重比例(weight)或是輪詢機制(round robin)，無法依據目前網路狀況做出更好判斷。 為改善上述問題，本論文在軟體定義網路(SDN)環境下，使用交換機取代傳統防火牆設備，透過封包分析與信任觀測區間達到規則學習，並整合Snort入侵偵測系統，透過特徵比對，找出危害網路環境之封包，即時阻擋該危險流量。本論文也提出基於隨需(on demand)概念，動態調整防火牆規則，降低管理人員負擔。最後利用交換機擁有多個實體通訊埠的概念 ，依需求可自由調整對外及對內線路數量，不再受限於廠商規格，取代傳統多路寬頻負載平衡器，建構更彈性的架構。並透過收集交換機上的實體埠與資料流表中的資訊，即時評估網路狀況，加強負載平衡。為驗證本論文所提出之⽅法的有效性，我們使用Linux伺服器架設KVM、OpenvSwitch以及POX控制器實際建構SDN網路環境，透過發送封包對防火牆提出請求，以驗證實驗方法的正確性。 根據實驗結果顯示，本論文所提出之概念均能正確運作，有效降低調整防火牆所需之人工作業。在多路寬頻負載平衡器部分，本研究所提出之負載平衡方法，與round robin負載平衡方法相較之下，在最佳情況下，能有效提升約25%平均頻寬使用率，並降低約17.5%封包遺失率。 / Firewall is an important device that is responsible for securing internal network by separating Internet from Intranet, but here are several existing issues about the firewall. First, the firewall rules are set by the network admistrator manually. Along with the vigorous development of Internet technologies and great amount of applications of virtual technology in recent years. This work burdens the network adminstrator with a heavy workload. Second, the firewall is able to isolate the external network from harmful traffic, however, it can do nothing to the internal network. The common situation is to use IDS to detect the harmful packet, but it can only send an alert message to the adminstrater, no more actions can be done. Finally, most companies use several ISP connections to assure fault tolerance and use Multi-WAN load balancer to integrate those connections to enhance bandwidth utilization. But the number of WAN/LAN ports is set by the manufacturer, and the load balance algorithm is also limited by the manufacturer. It offers only a few algorithms (network-based features, round-robin, etc.), and there is no other way to provide more efficient algorithms. In order to resolve the mentioned problems, we propose an automatic firewall based Software Defined Network (SDN). We use Openflow switches to replace traditional firewalls, the system is able to learn the rules automaticlly by packet analysis during an observation interval. We aslo integrate Snort Intrusion Detection System (IDS) to localize the dangerous packets and block them immediately. Next, we propose an on-demand based dynamic firewall rules adjustment mechanism which is able to reduce management workload. Finally, we implement a Multi-WAN load balancer architecture and provide a more efficient load balance algorithm by collecting port usage and firewall rule information. In order to verify the proposed methods, we implement a SDN environment by using Linux Ubuntu servers with KVM, Open vSwitch and POX controller. According to the experiment result, it proves that the proposed method is able to reduce the firewall configuration effectively. In the Multi-WAN load balancer, experiment results show that our method outperforms round-robin argrithom in terms of average bandwidth utilization and packet loss rate by 25% and 17.5%, respectively.