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欢迎来到Riguz的小站！这是一个私人wiki，用来记录一些我的笔记。
查看“︁TCP Packet Example”︁的源代码
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TCP Packet Example
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TCP每个报文都有一个序列号，这个序列号在初始的时候是随机生成的（而不是直接使用0或者1），那么这样做的原因究竟是为什么？ = TCP 实例= 使用[https://www.wireshark.org/ Wireshark]和[https://sourceforge.net/projects/sockettest/ SocketTest]在本地进行数据发送和接收，可以抓取到TCP报文。首先使用SocketTest在本地(127.0.0.1)的10240端口上启动一个Socket服务器，然后使用它的客户端功能连接这个端口，并在Wireshark中监听本地回环网卡(localhost)，即可抓取到对应的数据包。 == 三次握手== [[File:Wireshark-lo-1.png|600px|3-way Handshake]] 可以看出，是一个标准的三次握手的过程，握手完成之后，服务端给客户端发送了一个Window Update。 === 1:客户端发送SYN=== <syntaxhighlight lang="lua"> Frame 13: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) on interface lo0, id 0 Null/Loopback Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1 Transmission Control Protocol, Src Port: 64255, Dst Port: 10240, Seq: 0, Len: 0 Source Port: 64255 Destination Port: 10240 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 0 (relative sequence number) Sequence number (raw): 3261314628 [Next sequence number: 1 (relative sequence number)] Acknowledgment number: 0 Acknowledgment number (raw): 0 1011 .... = Header Length: 44 bytes (11) Flags: 0x002 (SYN) Window size value: 65535 [Calculated window size: 65535] Checksum: 0xfe34 [unverified] [Checksum Status: Unverified] Urgent pointer: 0 Options: (24 bytes), Maximum segment size, No-Operation (NOP), Window scale, No-Operation (NOP), No-Operation (NOP), Timestamps, SACK permitted, End of Option List (EOL) TCP Option - Maximum segment size: 16344 bytes TCP Option - No-Operation (NOP) TCP Option - Window scale: 6 (multiply by 64) TCP Option - No-Operation (NOP) TCP Option - No-Operation (NOP) TCP Option - Timestamps: TSval 740812626, TSecr 0 TCP Option - SACK permitted TCP Option - End of Option List (EOL) [Timestamps] </syntaxhighlight> === 2:服务端回复SYN/ACK=== <syntaxhighlight lang="lua"> Frame 14: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) on interface lo0, id 0 Null/Loopback Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1 Transmission Control Protocol, Src Port: 10240, Dst Port: 64255, Seq: 0, Ack: 1, Len: 0 Source Port: 10240 Destination Port: 64255 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 0 (relative sequence number) Sequence number (raw): 1175996045 [Next sequence number: 1 (relative sequence number)] Acknowledgment number: 1 (relative ack number) Acknowledgment number (raw): 3261314629 1011 .... = Header Length: 44 bytes (11) Flags: 0x012 (SYN, ACK) Window size value: 65535 [Calculated window size: 65535] Checksum: 0xfe34 [unverified] [Checksum Status: Unverified] Urgent pointer: 0 Options: (24 bytes), Maximum segment size, No-Operation (NOP), Window scale, No-Operation (NOP), No-Operation (NOP), Timestamps, SACK permitted, End of Option List (EOL) TCP Option - Maximum segment size: 16344 bytes TCP Option - No-Operation (NOP) TCP Option - Window scale: 6 (multiply by 64) TCP Option - No-Operation (NOP) TCP Option - No-Operation (NOP) TCP Option - Timestamps: TSval 740812626, TSecr 740812626 TCP Option - SACK permitted TCP Option - End of Option List (EOL) [SEQ/ACK analysis] [Timestamps] </syntaxhighlight> === 3:客户端回复ACK=== <syntaxhighlight lang="lua"> Frame 15: 56 bytes on wire (448 bits), 56 bytes captured (448 bits) on interface lo0, id 0 Null/Loopback Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1 Transmission Control Protocol, Src Port: 64255, Dst Port: 10240, Seq: 1, Ack: 1, Len: 0 Source Port: 64255 Destination Port: 10240 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 1 (relative sequence number) Sequence number (raw): 3261314629 [Next sequence number: 1 (relative sequence number)] Acknowledgment number: 1 (relative ack number) Acknowledgment number (raw): 1175996046 1000 .... = Header Length: 32 bytes (8) Flags: 0x010 (ACK) Window size value: 6379 [Calculated window size: 408256] [Window size scaling factor: 64] Checksum: 0xfe28 [unverified] [Checksum Status: Unverified] Urgent pointer: 0 Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps TCP Option - No-Operation (NOP) TCP Option - No-Operation (NOP) TCP Option - Timestamps: TSval 740812626, TSecr 740812626 [SEQ/ACK analysis] [Timestamps] </syntaxhighlight> == 数据发送== 通过像服务器发送一个"helloworld"来查看数据是如何发送的： === 1:客户端发送PSH/ACK=== <syntaxhighlight lang="lua"> Transmission Control Protocol, Src Port: 64255, Dst Port: 10240, Seq: 1, Ack: 1, Len: 12 Source Port: 64255 Destination Port: 10240 [Stream index: 0] [TCP Segment Len: 12] Sequence number: 1 (relative sequence number) Sequence number (raw): 3261314629 [Next sequence number: 13 (relative sequence number)] Acknowledgment number: 1 (relative ack number) Acknowledgment number (raw): 1175996046 1000 .... = Header Length: 32 bytes (8) Flags: 0x018 (PSH, ACK) Window size value: 6379 [Calculated window size: 6379] [Window size scaling factor: -1 (unknown)] Checksum: 0xfe34 [unverified] [Checksum Status: Unverified] Urgent pointer: 0 Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps TCP Option - No-Operation (NOP) TCP Option - No-Operation (NOP) TCP Option - Timestamps: TSval 742069804, TSecr 740812626 [SEQ/ACK analysis] [Timestamps] TCP payload (12 bytes) </syntaxhighlight> === 2:服务端回复ACK=== <syntaxhighlight lang="lua"> Transmission Control Protocol, Src Port: 10240, Dst Port: 64255, Seq: 1, Ack: 13, Len: 0 Source Port: 10240 Destination Port: 64255 [Stream index: 0] [TCP Segment Len: 0] Sequence number: 1 (relative sequence number) Sequence number (raw): 1175996046 [Next sequence number: 1 (relative sequence number)] Acknowledgment number: 13 (relative ack number) Acknowledgment number (raw): 3261314641 1000 .... = Header Length: 32 bytes (8) Flags: 0x010 (ACK) Window size value: 6379 [Calculated window size: 6379] [Window size scaling factor: -1 (unknown)] Checksum: 0xfe28 [unverified] [Checksum Status: Unverified] Urgent pointer: 0 Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps TCP Option - No-Operation (NOP) TCP Option - No-Operation (NOP) TCP Option - Timestamps: TSval 742069804, TSecr 742069804 [SEQ/ACK analysis] [This is an ACK to the segment in frame: 13] [The RTT to ACK the segment was: 0.000040000 seconds] [Timestamps] </syntaxhighlight> = 序列号与ACK= # (Client) SYN, Seq=3261314628 # (Server) SYN/ACK, Seq=1175996045, ACK=3261314629= # (Client) ACK, Seq=3261314629, ACK=1175996046= # (Client) PSH/ACK, Seq=3261314629, ACK=1175996046, Data(12bytes)= # (Server) ACK, Seq=1175996046, ACK=3261314641= # (Client) FIN/ACK, Seq=3261314641, ACK=1175996046= # (Server) ACK, Seq=1175996046, ACK=3261314642= # (Server) FIN, ACK, Seq=1175996046, ACK=3261314642= # (Client) ACK, Seq=3261314642, ACK=1175996047= [[Category:Network]]
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TCP Packet Example
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