萬花筒寫輪眼之防火牆ALG技術之FTP協議穿牆術

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"FTP協議主動模式穿越SNAT","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"主動模式穿越SNAT主要用於FTP服務器部署在公網,客戶端需要通過SNAT轉換訪問服務器。如圖1-1所示,描述了FTP主動模式穿越SNAT時的工作流程,此時需要藉助ALG技術纔可以完成穿越防火牆。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/eb/eb8f3f18e665b5c8a25d1bce7042b2f6.png","alt":"防火牆ALG技術之FTP協議穿牆術","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"圖1-1 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FTP主動模式穿越DNAT流程圖","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如圖4-2-(a)和4-2-(b)所示,防火牆配置同“3.FTP協議被動模式穿越DNAT”章節所述,整個通信過程包括以下幾個階段:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"公網客戶端與私網服務器之間TCP的三次握手建立控制連接;","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"公網客戶端發送PORT命令,攜帶公網客戶端指定的用於數據連接的IP和PORT信息;","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"PORT命令到達防火牆時,報文載荷中的公網IP(106.120.12.2)和PORT(C=23360=91*256+64)不會進行NAT轉換,將原樣轉發至私網服務器;","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"私網服務器收到PORT命令後解析其內容,並主動向公網客戶端發送數據連接(源IP-192.168.12.2、目的IP-106.120.12.2、源端口-20、目的端口-C=23360),經防火牆NAT轉換後(源IP-106.120.22.2、目的IP-106.120.12.2、源端口-10011、目的端口-C=23360)發送至公網客戶端,從而實現公網客戶端訪問私網服務器。","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d3/d303afb3a21dbf4690c8193b728ef929.png","alt":"防火牆ALG技術之FTP協議穿牆術","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"圖4-2-(a) 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FTP主動模式穿越DNAT-Server","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"FTP協議穿越防火牆NAT小結","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"ALG應用在外部地址訪問內部地址的場景下。ALG如果發現報文頭部進行了NAT,並且進一步發現是一條FTP連接時,就需要對PORT/PASV命令中的IP和PORT進行轉換。這樣理解後總結上述幾種場景可以得出如下結論:","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"私網訪問公網時需要防火牆進行SNAT,主動模式外部地址(Server)訪問內部地址(Client)建立數據連接,因此需要ALG;而被動模式不涉及外部地址想訪問內部地址的過程,故不需要ALG。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"公網訪問私網時需要防火牆進行DNAT,被動模式外部地址(Client)訪問內部地址(Server)建立數據連接,因此需要ALG;而主動模式不涉及外部地址想訪問內部地址的過程,故不需要ALG。","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"附件-FTP協議穿越NAT抓包","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"01_FTP主動模式穿越SNAT-Client.pcap","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"02_FTP主動模式穿越SNAT-Server.pcap","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"03_FTP被動模式穿越SNAT-Client.pcap","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"04_FTP被動模式穿越SNAT-Server.pcap","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"05_FTP被動模式穿越DNAT-Client.pcap","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"06_FTP被動模式穿越DNAT-Server.pcap","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"07_FTP主動模式穿越DNAT-Client.pcap","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"08_FTP主動模式穿越DNAT-Server.pcap","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"​","attrs":{}}]}]}
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