TFTP协议

た入场券 2022-09-07 06:25 246阅读 0赞

# 1.TFTP协议 #

TFTP协议全称为简单文件传输协议，它是以UDP为基础的应用层协议。在实现TFTP服务器之前，需要详细理解协议。目前很多介绍TFTP协议的书籍都是参照RFC1350，比如著名的《TCP/IP详解》。然而RFC1350已经被后来RFC2347、RFC2348、RFC2349等所代替，因此我们需要系统的认识一下这些最新的协议。

## 1.1 TFTP协议简介 ##

1992年，修订版TFTP协议RFC1350发布，这一版本的TFTP协议被广泛使用，《TCP/IP详解卷1》章节15讲解TFTP协议时便是使用的这个版本。

除非一些非常古老的TFTP客户端/服务器软件，目前主流的客户端/服务器软件都会支持TFTP扩展选项，1998年发布的RFC2347定义了TFTP扩展选项。扩展选项可以允许客户端和服务器之间进行协商，以便使用一些额外的功能，比如超时时间、文件大小、数据包大小等等。TFTP扩展选项增加一个新的选项应答（OACK）数据帧，用来应答客户端的选项协商请求，增加一个新的错误码（8），用来指示当进行选项协商出错时，终止数据传输。

1998年颁布的RFC2348定义了数据块大小选项（blksize），同年颁布的RFC2349定义了超时间隔（timeout）和文件大小（tsize）选项。

注：本文所有“字节”均由8bit构成。

## 1.2 TFTP协议概述 ##

数据传输起始于一个读取或者写入文件的请求，只有客户端才可以发送这种请求。

默认情况下，数据以定长512字节传输，如果服务器支持扩展选项，可以使用blksize选项协商数据长度。每个数据包中仅包含一个数据块。只有收到对方的应答数据包，才会发送下一包数据。

如果一个数据包数据大小小于512字节或小于通过blksize选项协商定的数据长度，表示数据传输结束。

两台机器进行数据传输时，一台为发送方一台为接收方。发送方发送数据并接收应答，接收方发送应答接收数据。

大部分的错误会导致连接中断，错误由一个错误的数据包引起，这个包不会被确认，也不会被重新发送。

## 1.3 TFTP协议传输模式 ##

TFTP协议支持三种传输模式，分别为：

*  netascii：ASCII文本模式
 *  octet：二进制模式，每字节8位
 *  mail：现在已经不使用

## 1.4 TFTP协议数据包种类 ##

TFTP协议支持六种数据包格式，如表2-1所示。

![20210822184206490.png][]

### 1.4.1读写请求数据包 ###

RFC2347规定的TFTP选项字段附加于读请求和写请求数据帧中。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODIzOTg1Ng_size_16_color_FFFFFF_t_70][]

1.4.1.1常用的选项：blksize

协商数据块大小，默认数据块为512，可以协商的值为8~65464字节（RFC2348）。

1.4.1.2 常用选项：timeout

超时间隔，可以协商的值为1~255秒（RFC2349）

1.4.1.3常用选项：tsize

传输文件的大小（RFC2349）

### 1.4.2 Data数据包 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODIzOTg1Ng_size_16_color_FFFFFF_t_70 1][]

### 1.4.3 ACK数据包 ###

![20210822184317679.png][]

1.4.4 ERROR数据包

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODIzOTg1Ng_size_16_color_FFFFFF_t_70 2][]

### 1.4.5 OACK包格式 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODIzOTg1Ng_size_16_color_FFFFFF_t_70 3][]

# 2、实验日志记录 #

## 2.1 没有加 -b选项 ##

root@ubuntu:/home/liuxl/code/code/source/busybox-1.23.0/_install/usr/bin# ./tftp -g -r 1.txt 192.168.31.175
    ==== LXL1 tftp_main ====
    ==== LXL2 opt_complementary:[g:p:g--p:p--g:] ====
    ==== LXL3 argv:[A] optind:[4] ====
    ==== LXL4 blksize:[512] ====
    ==== LXL4-1 host:[192.168.31.175] cp:[(null)] ====
    ==== LXL5 argv[0]:[192.168.31.175] argv[1]:[(null)] port:[69] ====
    ==== LXL6 using server '192.168.31.175:69', remote_file '1.txt', local_file '1.txt'
    ==== LXL6-1 io_bufsize:[516] ====
    ==== LXL6-2 local_fd:[1] ====
    ==== LXL6-2-1 pathname:[1.txt] flags:[577] mode:[438] ====
    ==== LXL6-3 first packet:[1.txt] ====
    send:[
    第一次发送请求：
    00 01 1  .  t  x  t  \0 o  c  t  e  t  \0 t  s  i  z  e  \0 0  \0  
    00 01 31 2e 74 78 74 00 6f 63 74 65 74 00 74 73 69 7a 65 00 30 00
    ]recv:[
    收到文件的大小
    \0 06 t  s  i  z  e  \0 2  1
    00 06 74 73 69 7a 65 00 32 31 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    ]==== LXL6-3 first packet:[] ====
    send:[
    00 04 00 00
    ]recv:[
    00 03 00 01 e5 8e bb e7 8e a9 e5 84 bf e7 be a4 e7 bf 81 e7 be a4 e7 bf 81 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    ]==== LXL6-3 first packet:[] ====
    send:[
    00 04 00 01
    1.txt                100% |***********************************************************************************************|    21   0:00:00 ETA

## 2.2 添加-b选项，每个包64字节 ##

root@ubuntu:/home/liuxl/code/code/source/busybox-1.23.0/_install/usr/bin# ./tftp -g -r 1.txt 192.168.31.175 -b 64
    ==== LXL1 tftp_main ====
    ==== LXL2 opt_complementary:[g:p:g--p:p--g:] ====
    ==== LXL3 argv:[;7] optind:[6] ====
    ==== LXL4 blksize:[64] ====
    ==== LXL4-1 host:[192.168.31.175] cp:[(null)] ====
    ==== LXL5 argv[0]:[192.168.31.175] argv[1]:[(null)] port:[69] ====
    ==== LXL6 using server '192.168.31.175:69', remote_file '1.txt', local_file '1.txt'
    ==== LXL6-1 io_bufsize:[68] ====
    ==== LXL6-2 local_fd:[1] ====
    ==== LXL6-2-1 pathname:[1.txt] flags:[577] mode:[438] ====
    ==== LXL6-3 first packet:[1.txt] ====
    send:[
    00 01 1  .  t  x  t  \0 o  c  t  e  t  \0 b  l  k  s  i  z  e  \0 6  4  \0 t  s  i  z  e  \0 0  \0
    00 01 31 2e 74 78 74 00 6f 63 74 65 74 00 62 6c 6b 73 69 7a 65 00 36 34 00 74 73 69 7a 65 00 30 00
    ]recv:[
    \0 6  b  l  k  s  i  z  e  \0 6  4  \0 t  s  i  z  e  \0 2  1
    00 06 62 6c 6b 73 69 7a 65 00 36 34 00 74 73 69 7a 65 00 32 31 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    ]==== LXL6-3 first packet:[] ====
    send:[
    00 04 00 00
    ]recv:[
    00 03 00 01 e5 8e bb e7 8e a9 e5 84 bf e7 be a4 e7 bf 81 e7 be a4 e7 bf 81 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    ]==== LXL6-3 first packet:[] ====
    send:[
    00 04 00 01
    
    
    1.txt                100% |***********************************************************************************************|    21   0:00:00 ETA

[20210822184206490.png]: /images/20220829/48946c34307441f58e25e8a78084fc34.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODIzOTg1Ng_size_16_color_FFFFFF_t_70]: /images/20220829/6475968359fb4ea1ae4b544db9f852f6.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODIzOTg1Ng_size_16_color_FFFFFF_t_70 1]: /images/20220829/b79d789f849e434b95bea42d438682d8.png
[20210822184317679.png]: /images/20220829/f3562cfce9904f9ea8e4076920b7796d.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODIzOTg1Ng_size_16_color_FFFFFF_t_70 2]: /images/20220829/487aa5f990854ba886de054ef38cd696.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODIzOTg1Ng_size_16_color_FFFFFF_t_70 3]: /images/20220829/ea63ad1861474baa83e41f5d9de12bf7.png