計算機網絡基礎(七)---網絡層-ICMP協議

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"文章內容概覽"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/99/99c390afa76faa67c10d669b115844fc.png","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"ICMP協議詳解"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"網際控制報文協議（Internet Control Message Protocol）"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"該協議主要是用於輔助IP協議進行數據傳輸的"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"ICMP協議"},{"type":"text","marks":[{"type":"strong"}],"text":"可以報告錯誤信息或者異常情況"}]}]}]},{"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","marks":[{"type":"strong"}],"text":"ICMP的報文數據是通過封裝在IP數據報中進行數據傳輸的"},{"type":"text","text":"。ICMP的報文分爲兩個部分：ICMP報文首部和ICMP報文數據"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/0c/0c3fa34b0dc935d512bc2099c196a50c.png","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"ICMP報文首部"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/07/07ebb633f98907dd933bc3813a76c92e.png","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"類型"},{"type":"text","text":"：主要指的是ICMP報文的種類(主要有兩大類，後邊會進行說明)"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"代碼"},{"type":"text","text":"：主要是指，不同的ICMP報文種類具體有哪些錯誤"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"校驗和"},{"type":"text","text":"：主要是校驗報文在整個傳輸中，是否存在錯誤"}]}]}]},{"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":"在前邊介紹IP協議首部中，有一個8位協議，它表明的是IP數據所攜帶的具體數據是什麼協議的。ICMP的字段值爲1"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/0b/0b2618dc8c86b98de76118c1def17c15.png","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"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":"如果IP協議傳輸的數據是ICMP數據的話，那麼，將會在協議中寫入1"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b8/b82ce19fd0e8d9d21c5c464b4ac9a8d3.png","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"ICMP協議報文的兩個種類"}]},{"type":"heading","attrs":{"align":null,"level":5},"content":[{"type":"text","text":"差錯報告報文"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f5/f5756b405f4cfab9d09118d41aa10159.png","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"網絡不可達"},{"type":"text","text":"：IP地址可以表示一個網絡，當主機號全爲0時就表示的是某一個網絡，如果整個網絡不可達，就會報告一個類型爲3，具體代碼爲0的ICMP協議報文"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"主機不可達"},{"type":"text","text":"：如果計算機A要和計算機B進行通信，而計算機B是關機的狀態，就會出現主機不可達的情況"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"網絡重定向"},{"type":"text","text":"：傳輸給某一個網絡的數據，可能不能走該網絡了，需要進行重定向"}]}]},{"type":"listitem","content":[{"type":"pa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192.168.0.1或者ping 192.168.1.1。如果上一步ping網關也是通的，說明本機到路由器是通的，如果不通，說明網線或者wifi是有問題的"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果ping網關是通的，則ping遠端地址（比如百度）。如果不通，則說明在你家到ISP之間網絡是故障的，這個時候就需要聯繫電信或移動或聯通"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"Traceroute應用"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"Traceroute可以探測IP數據報在網絡中走的路徑"},{"type":"text","text":"，在"},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/1305a459158b19e5c7bbecaaa","title":""},"content":[{"type":"text","text":"IP協議詳解"}]},{"type":"text","text":"這篇文章中，有介紹到計算機是連接在虛擬互聯網絡中的，我們並不關心數據報在網絡中經過了哪些路徑。但是，如果需要對網絡故障進行排查的話，Traceroute應用可以提供更高級的功能，使我們更瞭解網絡是怎麼樣的"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"Traceroute應用原理"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在前邊介紹IP首部時，首部裏邊有一個TTL，表明IP數據報文在網絡中的壽命，每經過一個設備，TTL減1，當TTL爲0時，"},{"type":"text","marks":[{"type":"strong"}],"text":"網絡設備必須丟棄該報文"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/9f/9f8ef7916f79013b4387b00a72c38ecc.png","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"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":"當TTL爲0時，網絡設備必須丟棄該報文。但是，並沒有告訴丟棄的時候應該怎麼處理。瞭解了ICMP報文之後可以知道，如果網絡設備要丟棄報文，將會發送一個"},{"type":"text","marks":[{"type":"strong"}],"text":"ICMP終點不可達差錯報文"},{"type":"text","text":"。也就是說，它會報告一個錯誤，告訴源端主機，報文傳輸發生了錯誤，這樣源主機纔會察覺到問題。下邊是一個例子"}]},{"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":"藉助前邊用到的一個圖，該圖指示了從計算機A到計算機B的網絡走向，前邊的文章中提到，數據報文是一跳一跳的傳輸的，因此它會先後跳到中型網絡=》大型網絡=》中型網絡=》小型網絡=》計算機B。"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f9/f9eb2e163354e19237dcfcc4d0ced284.png","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"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":"Traceroute應用巧妙的應用了"},{"type":"text","marks":[{"type":"strong"}],"text":"ICMP差錯不可達報文"},{"type":"text","text":"的作用，爲了探測數據報走過的路徑，它"},{"type":"text","marks":[{"type":"strong"}],"text":"首先會封裝一個TTL爲1的IP報文"},{"type":"text","text":"。在上圖中，計算機A發送了一個TTL爲1的報文之後，到達中型網絡之後就會發現TTL爲0了，此時就會往源機器(也就是A)發出一個ICMP差錯不可達報文。此時，計算機A會記錄該中型網絡的IP。此時Traceroute會再封裝一個TTL爲2的請求報文，當數據到達大型網絡之後，TTL爲0了。大型網絡會丟棄該報文，並且向源機器發出一個ICMP差錯不可達報文。此時計算機A又會記錄大型網絡的IP。"},{"type":"text","marks":[{"type":"strong"}],"text":"TTL會依次的增加，直到收到了正常的迴應，表示說計算機A發送的報文，已經被B收到了"},{"type":"text","text":"。此時，計算機A已經收到了所有的路徑機器的信息，此時就可以輸出數據報在網絡中走過的路徑了"}]},{"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":"因此，Traceroute應用巧妙的應用了ICMP差錯不可達報文的作用，每次將TTL加1，直到到達目標機器，記錄經過的每一個機器的IP，因此來獲取路徑。這就是Traceroute應用的原理"}]},{"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":"看一波實際操作，在windows中可以使用"},{"type":"text","marks":[{"type":"strong"}],"text":"tracert+域名/IP"},{"type":"text","text":"的命令來查看輸出。Mac中有自帶的工具可以使用"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c1/c1d9380e922e3c8f7a3d81de30ce36d8.png","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"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":"首先是可以看到百度的地址爲：182.61.200.7。然後packets下邊第一跳就是我的內網路由器地址192.168.0.1。第二跳來到的是113.45.64.1，這個應該就是小區的內網IP。後邊的每一跳所經過的IP，可以直接在百度上搜一下是哪裏的IP"}]},{"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":"如果想看到更加詳細的跨省路徑，可以追蹤訪問github.com，因爲這個服務器在美國，所以會比較慢"}]},{"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":"在快速變化的技術中尋找不變，纔是一個技術人的核心競爭力。知行合一，理論結合實踐"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5e/5eb4b2fdb444b8c7257756dc6b23fada.png","alt":null,"title":"","style":[{"key":"width","value":"25%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}