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Some Interesting Health Facts You Must Know. - 0 views

1. When you are looking at someone you love, your pupils dilate, and they do the same when you are looking at someone you hate. 2. The human head is one-quarter of our total length at birth but on...

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started by puzznbuzzus on 15 Feb 17 no follow-up yet

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Mark Wilson on 11 Jul 16

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TCP 的那些事儿（上）酷壳 - CoolShell.cn | 酷壳 - CoolShell.cn - 0 views

coolshell.cn/11564.html

shared by ma_haijin on 11 Aug 16 - No Cached

TCP的包是没有IP地址的，那是IP层上的事。但是有源端口和目标端口。
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Sequence Number是包的序号，用来解决网络包乱序（reordering）问题。
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Acknowledgement Number就是ACK——用于确认收到，用来解决不丢包的问题。
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...14 more annotations...
Window又叫Advertised-Window，也就是著名的滑动窗口（Sliding Window），用于解决流控的。
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TCP Flag ，也就是包的类型，主要是用于操控TCP的状态机的。
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其实，网络上的传输是没有连接的，包括TCP也是一样的。而TCP所谓的“连接”，其实只不过是在通讯的双方维护一个“连接状态”，让它看上去好像有连接一样。所以，TCP的状态变换是非常重要的。
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这个号要作为以后的数据通信的序号，以保证应用层接收到的数据不会因为网络上的传输的问题而乱序（TCP会用这个序号来拼接数据）。
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关于建连接时SYN超时。试想一下，如果server端接到了clien发的SYN后回了SYN-ACK后client掉线了，server端没有收到client回来的ACK，那么，这个连接处于一个中间状态，即没成功，也没失败。于是，server端如果在一定时间内没有收到的TCP会重发SYN-ACK。在Linux下，默认重试次数为5次，重试的间隔时间从1s开始每次都翻售，5次的重试时间间隔为1s, 2s, 4s, 8s, 16s，总共31s，第5次发出后还要等32s都知道第5次也超时了，所以，总共需要 1s + 2s + 4s+ 8s+ 16s + 32s = 2^6 -1 = 63s，TCP才会把断开这个连接。
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请注意，请先千万别用tcp_syncookies来处理正常的大负载的连接的情况。因为，synccookies是妥协版的TCP协议，并不严谨。对于正常的请求，你应该调整三个TCP参数可供你选择，第一个是：tcp_synack_retries 可以用他来减少重试次数；第二个是：tcp_max_syn_backlog，可以增大SYN连接数；第三个是：tcp_abort_on_overflow 处理不过来干脆就直接拒绝连接了。
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一个ISN的周期大约是4.55个小时。因为，我们假设我们的TCP Segment在网络上的存活时间不会超过Maximum Segment Lifetime（缩写为MSL – Wikipedia语条），所以，只要MSL的值小于4.55小时，那么，我们就不会重用到ISN。
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为什么不直接给转成CLOSED状态呢？主要有两个原因：1）TIME_WAIT确保有足够的时间让对端收到了ACK，如果被动关闭的那方没有收到Ack，就会触发被动端重发Fin，一来一去正好2个MSL，2）有足够的时间让这个连接不会跟后面的连接混在一起（你要知道，有些自做主张的路由器会缓存IP数据包，如果连接被重用了，那么这些延迟收到的包就有可能会跟新连接混在一起）。
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Again，使用tcp_tw_reuse和tcp_tw_recycle来解决TIME_WAIT的问题是非常非常危险的，因为这两个参数违反了TCP协议
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如果你的服务器是于HTTP服务器，那么设置一个HTTP的KeepAlive有多重要（浏览器会重用一个TCP连接来处理多个HTTP请求）
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TCP要保证所有的数据包都可以到达，所以，必需要有重传机制。
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接收端给发送端的Ack确认只会确认最后一个连续的包，比如，发送端发了1,2,3,4,5一共五份数据，接收端收到了1，2，于是回ack 3，然后收到了4（注意此时3没收到），此时的TCP会怎么办？我们要知道，因为正如前面所说的，SeqNum和Ack是以字节数为单位，所以ack的时候，不能跳着确认，只能确认最大的连续收到的包，不然，发送端就以为之前的都收到了。
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TCP引入了一种叫Fast Retransmit 的算法，不以时间驱动，而以数据驱动重传。也就是说，如果，包没有连续到达，就ack最后那个可能被丢了的包，如果发送方连续收到3次相同的ack，就重传。Fast Retransmit的好处是不用等timeout了再重传。
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注意：SACK会消费发送方的资源，试想，如果一个攻击者给数据发送方发一堆SACK的选项，这会导致发送方开始要重传甚至遍历已经发出的数据，这会消耗很多发送端的资源。
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ma_haijin on 11 Aug 16

TCP是一个巨复杂的协议，因为他要解决很多问题，而这些问题又带出了很多子问题和阴暗面。所以学习TCP本身是个比较痛苦的过程，但对于学习的过程却能让人有很多收获。关于TCP这个协议的细节，我还是推荐你去看W.Richard Stevens的《TCP/IP 详解卷1：协议》（当然，你也可以去读一下RFC793以及后面N多的RFC）。另外，本文我会使用英文术语，这样方便你通过这些英文关键词来查找相关的技术文档。之所以想写这篇文章，目的有三个，一个是想锻炼一下自己是否可以用简单的篇幅把这么复杂的TCP协议描清楚的能力。另一个是觉得现在的好多程序员基本上不会认认真真地读本书，喜欢快餐文化，所以，希望这篇快餐文章可以让你对TCP这个古典技术有所了解，并能体会到软件设计中的种种难处。并且你可以从中有一些软件设计上的收获。最重要的希望这些基础知识可以让你搞清很多以前一些似是而非的东西，并且你能意识到基础的重要。所以，本文不会面面俱到，只是对TCP协议、算法和原理的科普。我本来只想写一个篇幅的文章的，但是TCP真TMD的复杂，比C++复杂多了，这30多年来，各种优化变种争论和修改。所以，写着写着就发现只有砍成两篇。上篇中，主要向你介绍TCP协议的定义和丢包时的重传机制。下篇中，重点介绍TCP的流迭、拥塞处理。废话少说，首先，我们需要知道TCP在网络OSI的七层模型中的第四层--Transport层，IP在第三层--Network层，ARP在第二层--Data Link层，在第二层上的数据，我们叫Frame，在第三层上的数据叫Packet，第四层的数据叫Segment。首先，我们需要知道，我们程序的数据首先会打到TCP的Segment中，然后TCP的Segment会打到IP的Packet中，然后再打到以太网Ethernet的Frame中�

<div class="cArrow"> </div><div class="cContentInner">TCP是一个巨复杂的协议，因为他要解决很多问题，而这些问题又带出了很多子问题和阴暗面。所以学习TCP本身是个比较痛苦的过程，但对于学习的过程却能让人有很多收获。关于TCP这个协议的细节，我还是推荐你去看W.Richard Stevens的《TCP/IP 详解卷1：协议》（当然，你也可以去读一下RFC793以及后面N多的RFC）。另外，本文我会使用英文术语，这样方便你通过这些英文关键词来查找相关的技术文档。之所以想写这篇文章，目的有三个，一个是想锻炼一下自己是否可以用简单的篇幅把这么复杂的TCP协议描清楚的能力。另一个是觉得现在的好多程序员基本上不会认认真真地读本书，喜欢快餐文化，所以，希望这篇快餐文章可以让你对TCP这个古典技术有所了解，并能体会到软件设计中的种种难处。并且你可以从中有一些软件设计上的收获。最重要的希望这些基础知识可以让你搞清很多以前一些似是而非的东西，并且你能意识到基础的重要。所以，本文不会面面俱到，只是对TCP协议、算法和原理的科普。我本来只想写一个篇幅的文章的，但是TCP真TMD的复杂，比C++复杂多了，这30多年来，各种优化变种争论和修改。所以，写着写着就发现只有砍成两篇。上篇中，主要向你介绍TCP协议的定义和丢包时的重传机制。下篇中，重点介绍TCP的流迭、拥塞处理。废话少说，首先，我们需要知道TCP在网络OSI的七层模型中的第四层--Transport层，IP在第三层--Network层，ARP在第二层--Data Link层，在第二层上的数据，我们叫Frame，在第三层上的数据叫Packet，第四层的数据叫Segment。首先，我们需要知道，我们程序的数据首先会打到TCP的Segment中，然后TCP的Segment会打到IP的Packet中，然后再打到以太网Ethernet的Frame中�</div>

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How Speeding The "Most Important Algorithm Of Our Lifetime" Could Change This Modern Wo... - 0 views

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shared by Edmond Lau on 24 Jan 12 - No Cached

Fun Experience with Professional Wedding Photography in Sydney - 1 views

Weddings are all about showing each other that you are in love and committed towards one another. It is an event that should be fun because it only happens once in a lifetime. Couples who are happy...

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started by Sydney Wedphoto on 27 Sep 11 no follow-up yet

IDM Universal Web Crack Latest Version Free Download For PC - 0 views

crackysoft on 25 Sep 21

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crackysoft on 25 Sep 21

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WinRAR Activator Latest Version Free Download With Full Crack - 0 views

crackysoft on 25 Sep 21

WinRAR Activator is a powerful archive manager that provides full support for RAR, ZIP archives and decompresses CAB, ARJ, LZH, TAR, GZ, ACE, UUE, BZ2, JAR, ISO, 7Z, Z files.

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Buy Facebook 5 Star Reviews - 100% Non-Drop,Safe,Real 5 Star Reviews - 0 views

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shared by jackmcmahon4 on 06 Aug 23 - No Cached

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<div class="cArrow"> </div><div class="cContentInner">Buy Facebook 5 Star Reviews Introduction Facebook is a great marketing tool for businesses. You can use it as a way to increase your visibility and get more customers. You can also use this platform to advertise your business and promote products, services or events that you offer. However, if you don't have any reviews on your page then it will be hard for people to find out about these things because they won't know much about your brand or what makes you different from other companies in the area Facebook 5 star reviews Facebook reviews are the most important things for your business. If you want to increase your ranking and get more visitors, then you must buy facebook 5 star reviews. Do you guarantee to buy facebook 5 star reviews? Facebook is one of the best websites to find customers on because it's so popular, but how do you know what type of content works best? There are many different ways to get people interested in visiting your page and checking out what you have available for purchase or download. Some may not even realize that they're spending money when they buy something from a third party through Facebook Marketplace or through an app like Instagram Stories where ads pop up randomly throughout their feed without any warning beforehand (this has led some businesses think about shutting down their accounts). Buy Facebook 5 Star Reviews in Local Business If you want to buy facebook 5 star reviews, then we are the best place for that. We offer a wide range of reviews and rating systems that will get your page noticed by potential customers. Our team of experts is always available to help your business grow in an efficient manner. You can contact us at any time if you have any questions regarding our services or if there's something else that we can do for you! Buy Facebook 5 Star Reviews Facebook 5 Star Reviews Get Real 5-star rating on your Facebook Page. Facebook is a great platform for social media marketing and sales. It has over 2 b</div>

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shared by zytrailerparts on 30 Aug 22 - No Cached

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