微网站建设平台,如何自己制作链接内容,网上商城都有哪些,seo兼职1. tcp out-of-order#xff08;tcp有问题#xff09; 解答#xff1a; 1#xff09;、 应该有很多原因。但是多半是网络拥塞#xff0c;导致顺序包抵达时间不同#xff0c;延时太长#xff0c;或者包丢失#xff0c;需要重新组合数据单元 因为他们可能是通过不同的路径…1. tcp out-of-ordertcp有问题 解答 1、 应该有很多原因。但是多半是网络拥塞导致顺序包抵达时间不同延时太长或者包丢失需要重新组合数据单元 因为他们可能是通过不同的路径到达你电脑上面的。 2、 CRM IT 同仁上礼拜来跟我反应一个问题由他们客服系统藉由邮件主机要寄送给客户的信件常常会有寄送失败的问题查看了一下 Log发现正常的信件在主机接收 DATA 完成后会记录收到的邮件大小然后开始进行后续寄送出去的处理但这些有问题的寄送都会发生 DATA 没有传送完Server 就记录已读取到 EOF然后结束连线也因此这封信就不算顺利的送到 Server 上来。 初步看了一下排除是 Timeout 问题因为连线断的时间都还未达设定的连线 Timeout 时间由于 CRM 系统是外面厂商写的为了厘清问题我只好抓封包来看是不是用户端送出来结束传送的指令的。 抓了一下结果如下 整封邮件的传送过程包含了大量的 TCP Retransmission 或是 Segment Lost到后来还有跑出 TCP Out-Of-Order看起来是网路的问题网路上对于 TCP Out-Of-Order 的建议是说有些 Packet 可能 Lost所以重新传送造成另一个可能是因为 Client 到 Server 间有两条网路路径像是 Load Balance 之类的架构因此若两个封包走不同路径晚送的封包却比早送的到达就会发生 Out-Of-Order。 因此在断定有可能是网路造成加上 CRM 系统上的网卡同事是把两张做成一张 Virtual再请他拿掉 Bonding 只用单一张跑以后问题就不存在了观察流量还跑的比原本两张合起来的 Virtual 单张跑的高所以 M$ 在 Bonding 网卡上是不是还有什么需要调整的就不得而之了至少找出造成大量寄送失败的原因就好。 2. tcp segment of a reassembled PDU 解答1在连个连接建立的时候SYN包里面会把彼此TCP最大的报文段长度在局域网内一般都是1460.如果发送的包比最大的报文段长度长的话就要分片了被分片出来的包就会被标记了“TCP segment of a reassembled PDU”可以参考下图看一下被标记了的包的SEQ和ACK都和原来的包一致 2上周在公司里遇到一个问题用wireshark抓系统给网管上报的数据发现里面有好多报文被标识为“TCP segment of a reassembled PDU”并且每一段报文都是180Byte当时看到这样的标识觉得是IP报文分片以为系统的接口MTU值为设置小了通过命令查询发现是1500没有被重设过当时有点想不通。 回来查了一下发现自己的理解是错的“TCP segment of a reassembled PDU”指的不是IP层的分片IP分片在wireshark里用“Fragmented IP protocol”来标识。详细查了一下发现“TCP segment of a reassembled PDU”指TCP层收到上层大块报文后分解成段后发出去。于是有个疑问TCP层完全可以把大段报文丢给IP层让IP层完成分段为什么要在TCP层分呢其实这个是由TCP的MSS(Maximum Segment Size最大报文段长度)决定的TCP在发起连接的第一个报文的TCP头里通过MSS这个可选项告知对方本端能够接收的最大报文当然这个大小是TCP净荷的大小以太网上这个值一般设置成1460因为1460Byte净荷20Byte TCP头20Byte IP头 1500字节正好符合链路层最大报文的要求。 至于收到一个报文后如何确定它是一个”TCP segment”如果有几个报文的ACK序号都一样并且这些报文的Sequence Number都不一样并且后一个Sequence Number为前一个Sequence Number加上前一个报文大小再加上1的话肯定是TCP segment了对于没有ACK标志时则无法判断。 既然收到的TCP报文都是180Byte的segment那么应该是协商的时候PC端告知了MSS为180Byte至于为什么这样只能等抓包后确认是MSS的问题再排查了。另外有一种情况也可能导致这个问题被测系统因为MTU为220Byte而设置MSS为180Byte但是这种情况现在可以排除因为前面讲过已经查询过MTU值为1500。 3. Tcp previous segment losttcp先前的分片丢失 解答 1、“TCP Previous segment lost” errors are not “fatal” errors. They simply indicate that the sequence number in the arriving packet is higher than the next-expected sequence number, indicating that at least one segment was dropped/lost. The receiving station remedies this situation by sending duplicate ACKs for each additional packet it receives until the sender retransmits the missing packet(s). TCP is designed to recover from this situation, which is why the image is downloaded correctly despite having a (briefly) missing packet. If you are getting a large number of lost packets, then there is likely a communication problem between the sender and receiver. A common cause of this is un-matched duplex settings between the PC and the switch. We (our lab) recently upgraded to Ethereal 0.10.14 with WinPCap 3.1. If I remember correctly, we had previously been using 0.10.2 with WinPCap 3.0. However, since the upgrade we have been noticing several issues. The first issue is with “TCP Previous segment lost” and “TCP CHECKSUM INCORRECT” messages appearing in the Packet Listing window. We do not remember seeing these in the previous version of Ethereal, or at least not nearly as many as we are seeing now. For example, one task for the student instructional part of the lab involves visiting a website containing two images and observing the network activity. After the two GET requests are sent for the images, it is not uncommon for one image to be returned with a typical 200 OK response packet, but the response packet for the other image will be displayed as “TCP Previous segment lost.” However, both images are downloaded and displayed perfectly fine in the browser. I would think that the segment lost error would mean the object wasn’t returned correctly and shouldn’t be able to be displayed, but apparently that is not the case. (The cache had been cleared when this was performed, so it was not defaulting to a local copy of the image.) Another problem we’ve been noticing is that some packets simply aren’t displayed in the Packet Listing window, even when they are obviously received. Using the same example as above, after the two GET requests are sent for the images, it is not uncommon for one image to be returned with a typical 200 OK response, but the other response will not appear. Yet both images are successfully displayed in the browser. Is this a problem with Ethereal not detecting the packets? I’m not sure how typical this is, but we seem to be experiencing these issues often with 0.10.14 while we never did with 0.10.2. Could it also be an issue with WinPCap, and not necessarily Ethereal? I’m just trying to find some answers as to why we are seeing a sudden abundance of TCP related errors and uncaptured packets. Thanks. 2、I have a network client application that runs fine while I am debugging (no TCP errors), but when I run the release version, it runs incredibly slow. It runs as a series of transactions, where each transaction is a separate connection to the server. Wireshark analysis has determined that about 50% of all transactions involve the series: TCP Previous Segment Lost TCP Dup ACK RST The RST consumes 3 seconds per transaction, which is a Big Deal. So to prevent it, I must prevent the initial “TCP Previous Segment Lost” (which seems, on the surface, to merely be a time-out on a particular segment). In the following clip, the SYN packet suffers from the “TCP Previous Segment Lost” condition. 0.000640 seconds seems like too short of a time to declare this condition, as many previous successful transactions took much longer to be successfully SYN-ACK’ed. Can somebody explain “TCP Previous Segment Lost” in this context to help me troubleshoot my problem? Any help would be appreciated. Here is a clip of a problem transaction: fffgs 4. Tcpacked lost segmenttcp应答丢失 5. Tcp window updatetcp窗口更新 6. Tcp dup acktcp重复应答 TCP may generate an immediate acknowledgment (a duplicate ACK) when an out- of-order segment is received. This duplicate ACK should not be delayed. The purpose of this duplicate ACK is to let the other end know that a segment was received out of order, and to tell it what sequence number is expected. 当收到一个出问题的分片Tcp立即产生一个应答。这个相同的ack不会延迟。这个相同应答的意图是让对端知道一个分片被收到的时候出现问题并且告诉它希望得到的序列号。 Since TCP does not know whether a duplicate ACK is caused by a lost segment or just a reordering of segments, it waits for a small number of duplicate ACKs to be received. It is assumed that if there is just a reordering of the segments, there will be only one or two duplicate ACKs before the reordered segment is processed, which will then generate a new ACK. If three or more duplicate ACKs are received in a row, it is a strong indication that a segment has been lost. TCP then performs a retransmission of what appears to be the missing segment, without waiting for a retransmission timer to expire. 7. Tcp keep alivetcp保持活动 在TCP中有一个Keep-alive的机制可以检测死连接原理很简单TCP会在空闲了一定时间后发送数据给对方 1.如果主机可达对方就会响应ACK应答就认为是存活的。 2.如果可达但应用程序退出对方就发RST应答发送TCP撤消连接。 3.如果可达但应用程序崩溃对方就发FIN消息。 4.如果对方主机不响应ack, rst继续发送直到超时就撤消连接。这个时间就是默认 的二个小时。 uses WinSock2; procedure TForm1.IdTCPServer1Connect(AThread: TIdPeerThread); type TCP_KeepAlive record OnOff: Cardinal; KeepAliveTime: Cardinal; KeepAliveInterval: Cardinal end; var Val: TCP_KeepAlive; Ret: DWord; begin Val.OnOff:1; Val.KeepAliveTime:6000; //6s Val.KeepAliveInterval:6000; //6s WSAIoctl(AThread.Connection.Socket.Binding.Handle, IOC_IN or IOC_VENDOR or 4, Val, SizeOf(Val), nil, 0, Ret, nil, nil) end; ——————————————————– KeepAliveTime值控制 TCP/IP 尝试验证空闲连接是否完好的频率。如果这段时间内没有活动则会发送保持活动信号。如果网络工作正常而且接收方是活动的它就会响应。如果需要对丢失接收方敏感换句话说需要更快地发现丢失了接收方请考虑减小这个值。如果长期不活动的空闲连接出现次数较多而丢失接收方的情况出现较少您可能会要提高该值以减少开销。缺省情况下如果空闲连接 7200000 毫秒2 小时内没有活动Windows 就发送保持活动的消息。通常1800000 毫秒是首选值从而一半的已关闭连接会在 30 分钟内被检测到。 KeepAliveInterval值定义了如果未从接收方收到保持活动消息的响应TCP/IP 重复发送保持活动信号的频率。当连续发送保持活动信号、但未收到响应的次数超出TcpMaxDataRetransmissions的值时会放弃该连接。如果期望较长的响应时间您可能需要提高该值以减少开销。如果需要减少花在验证接收方是否已丢失上的时间请考虑减小该值或TcpMaxDataRetransmissions值。缺省情况下在未收到响应而重新发送保持活动的消息之前Windows 会等待 1000 毫秒1 秒。 KeepAliveTime根据你的需要设置就行比如10分钟注意要转换成MS。 XXX代表这个间隔值得大小 8. Tcp retransmissiontcp重传 作为一个可靠的传输协议传输控制协议TCP在发送主机需要从目标主机收到一个包时确认。If the sender does not receive that acknowledgment within a certain amount of time, it acts under the assumption that the packet did not reach its destination and retransmits the packet.如果发件人没有收到的时间内一定之金额确认它的行为假设下该数据包没有到达其目的地以及转发数据包。 原文链接http://www.xianren.org/net/wireshark-q.html转载于:https://www.cnblogs.com/amwuau/p/8317270.html
