TFTP or Trivial File Transfer Protocol is a simple file transfer protocol that is used to transfer files via the network in a simple way. TFTP is created as a lightweight alternative to the more advanced FTP protocol. The TFTP protocol has some advantages over other protocols like FTP, SCP, SFTP, etc.
TFTP Advantages
- Easy to access with a simpler protocol.
- Simple to implement
- Less bandwidth usage with less control overhead.
- Faster
TFTP Server Port
First of all, TFTP is a UDP-based protocol. Other protocols like FTP, SCP, and SFTP use the TCP protocol for communication. UDP protocol is generally used to transmit bulk and binary data from server to client or client to server. UDP protocol is lightweight and it does not use complex session protocols. The TFTP default port number is UDP 69 for TFTP servers.
TFTP Client Port
TFTP client does not have a fixed port number which changes for every connection. Generally, the non-prvileged ports are assigned as TFTP client port numbers. The non-privileged UDP ports start from 1024 and up to 65535.
List Running TFTP with Port Number In Linux
The netstat command can be used to list running TFTP server or service with its port number.
$ netstat -uln
List Running TFTP with Port Number In Linux
- Запросы на чтение и запись
- Процесс передачи данных
Применение
Основное назначение TFTP — обеспечение простоты реализации клиента. В связи с этим он используется для загрузки бездисковых рабочих станций, загрузки обновлений и конфигураций в «умные» сетевые устройства, записи статистики с мини-АТС (CDR) и аппаратных маршрутизаторов/файрволов.
Безопасность
Поскольку протокол не поддерживает аутентификации, единственный метод идентификации клиента — это его сетевой адрес (который может быть подделан). Обычно в Unix-системах tftpd доступен только каталог /tftpboot. Однако в старых TFTP-серверах было возможным получить файл паролей командой GET ../etc/passwd.
Дополнительная защита от доступа к произвольным файлам осуществляется с помощью на каталог tftpd (обычно /usr/TFTPRoot).
Типы пакета
Сначала в TFTP-пакете идет поле размером в 2 байта, определяющее тип пакета:
- Read Request (RRQ, #1) — запрос на чтение файла.
- Write Request (WRQ, #2) — запрос на запись файла.
- Data (DATA, #3) — данные, передаваемые через TFTP.
- Acknowledgment (ACK, #4) — подтверждение пакета.
- Error (ERR, #5) — ошибка.
- Options Acknowledgment (OACK, #6) — подтверждение опций.
Запросы на чтение и запись
Для начала передачи данных клиент должен послать серверу WRQ или RRQ-пакет. У обоих пакетов формат одинаковый:
В TFTP существует 2 режима передачи (режим Mail, определенный в IEN 133, признан устаревшим):
- netascii — файл перед передачей перекодируется в ASCII.
- octet — файл передается без изменений.
Процесс передачи данных
После получения запроса RRQ, сервер сразу посылает в качестве подтверждения пакет с данными и с ID пакета равным единице. В WRQ в качестве подтверждения используется ACK с ID равным нулю. Всего по TFTP можно передать 32 Мб (65536 * 512 / 1024²), однако из-за использования знакового int вместо беззнакового, размер подтверждения ограничен 16 мегабайтами. Однако если клиент и сервер поддерживают расширения протокола RFC 2347 и RFC 2348, то максимальный размер передаваемого файла увеличивается до 4Gb.
Опции TFTP
В RFC 2347 был предусмотрен формат опций, которые можно присоединять к окончанию RRQ-пакета и WRQ-пакета:
Опций может быть несколько. Тогда они будут следовать друг за другом. Порядок опций не важен.
В ответ на RRQ (или WRQ) с опциями, сервер должен прислать OACK с списком опций, которые сервер принял. Наиболее распространённые опции:
Ошибки
В TFTP информация об ошибке имеет следующий формат:
Код ошибки может принимать одно из значений, перечисленных в STD 33 (за исключением кода 8 — он описан в RFC 2347). Вот они:
Схема URI
В RFC 3617 определен формат URI для TFTP. Он имеет следующий вид:
Стандарты
- У. Ричард Стивенс. «Протоколы TCP/IP. Практическое руководство». Глава 15, «Простейший протокол передачи файлов TFTP». ISBN 5-7940-0093-7
- Х. Остерлох. «TCP/IP. Семейство протоколов передачи данных в сетях компьютеров». Глава 16 «Простейший протокол передачи файлов (TFTP)». ISBN 5-93772-039-3
Ссылки
- WinAgents TFTP Server Сервер TFTP для Windows с поддержкой разграничения прав доступа
- TFTP Server TFTPDWIN Сервер TFTP для Windows
- tftpd(8) – страница помощи man в (англ.)
- Innerdive TFTP Server Сервер TFTP для Windows. Рассчитан на высокие нагрузки.
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SunOS 5.8 Last Revised 16 Jun 1999
The Trivial File Transfer Protocol (TFTP) provides a minimalistic means for transferring files. It is generally used as a part of PXE booting or for updating configuration and firmware on devices which have limited memory such as routers, IP phones and printers.
There are several TFTP server implementations, some of which are listed below.
Install and then start tftpd.service.
To modify service parameters edit /etc/conf.d/tftpd.
This server includes a useful URL rewriting feature via the –map-file option (–mapfile in some versions). It allows requests to be altered via regular expressions so the files on the server do not have to match the view the client sees, and different files can be returned to different clients even if they request the same file.
Configure a map by adding –map-file /etc/tftpd.map to /etc/conf.d/tftpd and creating a file such as this:
# Add the remote IP address as a folder on the front of all requests.
r ^ i/
This example file will result in each TFTP request being prefixed with the remote IP address. For example if the machine at 192.168.0.1 requests “boot.bin” and the TFTP server root is /srv/tftp then the file /srv/tftp/192.168.0.1/boot.bin will be returned (or /srv/tftp/::ffff:192.168.0.1/boot.bin if the server is listening on an IPv6 port).
The available map file options are documented in in.tftpd(8) § FILENAME REMAPPING.
The –verbosity 5 option can be used to turn on all debugging messages. This is very useful for diagnosing why a machine will not successfully boot from the network, as the debug messages list all requests for files, whether rewrite rules were used, where the files were read from on the filesystem and whether the request was successful or not.
It is not possible to log messages to stdout/stderr, as only syslog is supported. This means the messages can be viewed with journalctl or similar.
Install and then start atftpd.service.
To modify service parameters edit /etc/conf.d/atftpd.
AUR is a simple (T)FTP server that can be run from the command line:
# uftpd -n -o ftp=0,tftp=69 /tmp/tftp
The option -o ftp=0 disables the FTP server and only runs TFTP. The server runs in read-only mode by default and passing -o writable allows clients to put files on the server. The -o tftp=69 is redundant in the case of default port, but shows a way to select a different one.
Note: dnsmasq does not support file uploads.
See dnsmasq#TFTP server.
Install and then tftp your day away!
The package contains both a server and a client with interactive and batch mode. The client binary is atftp and supports both getting and putting files.
Standard has an ability to connect to a TFTP server and upload a file via:
$ curl -T FILE tftp://HOST
Download a file:
$ curl -o DESTINATION tftp://HOST/file
Where file is relative to the TFTP root directory.
Introduction
See Chapter 4 of the Installation and Configuration Guide for
information about configuring the TFTP server.
FTP-OpenVMS is a more complete file transfer facility than TFTP.
See Chapter 3, FTP: Transferring Files, for details
on FTP-OpenVMS.
Invoking TFTP
To invoke TFTP, enter at the DCL prompt:
If you specify a host name, TFTP uses that host for subsequent
file transfers. If you also specify a port number, TFTP uses the specified host
and port for subsequent file transfers.
Command Reference
TFTP offers 20-line recall on the command level.
CONNECT
Sets the host and, optionally, the port number for subsequent
file transfers. Note that TFTP uses UDP and, therefore, does not maintain the
connection between transfers.
Format
Name of the remote host to which you want to connect. The host
must exist on the network.
Service name or number of the remote port that you want to
connect to. The default port number is 69 for read and write requests. You do
not need to specify the port number unless you are connecting to a nonstandard
server.
Example
Each of these equivalent commands connects to host SIGMA for a
file transfer:
GET
Gets a file from the previously specified remote host. TFTP
writes the local file as a STREAM_LF formatted file.
Since TFTP does not authenticate the client, the server allows
access only to files in the directory and its subdirectories defined by the
TCPWARE_TFTP_ROOT logical.
The server converts UNIX filenames with their directories into
VMS filenames as in Table 13-1. The directory specification is dir and the
filename specification with its extension is filename.ext.
Input file specification on the remote host.
Output file specification on the local host. If omitted,
Client-TFTP uses the remote-file filename and extension.
Examples
1 This
command transfers the US-DOMAIN-INFO.TXT file from the previously specified
host:
2 This
command transfers the US-DOMAIN-INFO.TXT file from the previously specified
host as file LOCALSTUFF.TXT:
HELP
Displays a brief help message summarizing the commands.
Optional command for which you want help.
This command provides help for the CONNECT and GET commands:
MODE
Sets the file transfer mode to type; type may be either ASCII or
BINARY. The initial type is ASCII.
The mode type, either ASCII or BINARY.
This command changes the transfer mode to BINARY
PUT
Puts a file to the previously specified remote host.
The server converts OpenVMS filenames with their directories into
UNIX filenames as in Table 13-2. The directory specification is dir and the
filename specification with its extension is filename.ext.
Input file specification on the local host.
Output file specification on the remote host. If omitted,
Client-TFTP uses the local-file filename and extension.
1 This
command transfers the US-DOMAIN-INFO.TXT file to the previously specified host:
2 This
command transfers the US-DOMAIN-INFO.TXT file to the previously specified host
as file REMOTESTUFF.TXT:
QUIT
Exits the TFTP program. You can also use Ctrl/Z and EXIT to exit the
program.
Each of these equivalent commands exits from TFTP:
REXMT
Sets the retransmit timer, in seconds. The initial value is 5
seconds.
The value you enter for REXMT is also used together with the
specified maximum timeout (set using the TIMEOUT command) to determine the
number of times to try and the actual maximum timeout reported in a status
request (STATUS).
If the default 5 seconds retransmit interval is used together
with the default 25 seconds maximum timeout, the number of times to try is 5,
according to the formula:
Max-timeout = Rexmt-interval x Tries
The REXMT value you enter is always reported (unchanged) on the line in a STATUS
request. However, the maximum timeout may be recalculated before being reported
as .
See theTIMEOUT command for details on recalculation.
The time value to set the retransmit timer. If omitted, the value
is 5 seconds.
This command changes the retransmit timer () to 10
seconds (and the subsequent STATUS command shows the result). The is set to five
times the by
default.
STATUS
Displays the current status and parameter settings.
The number of tries () is initially 5 unless adjustments are made to the and values (see
below for an example).
The total
retransmission period ()
value displayed may be slightly different from that set using the TIMEOUT
command. (See theTIMEOUT command for an explanation.)
This command shows the connection status, file transfer mode (), packet trace flag
status (),
retransmit timer (),
and total retransmission period (
values over the period of a number of adjustments. (See theTIMEOUT command for an explanation of the recalculations.)
TIMEOUT
Sets the total retransmission period, in seconds. The initial
value is 25 seconds.
The Tries value must be an integer value. Thus, if the
Max-timeout specified using the TIMEOUT command forms a non-integer ratio with
the Rexmt-interval value, the Max-timeout is adjusted accordingly. (See the
example.)
The total retransmission period, in seconds. If omitted, the
value is 25 seconds.
Note the way in which the retransmission period is adjusted in
this example:
The retransmit timer
and number of tries are both set to 5 by default, so that initially the is 25.
With the retransmit timer () reset to 4, the changes to 4 x 5 = 20.
Changing the maximum
timeout to 30 (with the
still set to 4) recalculates the retries to 7, and adjusts the to 4 x 7 = 28.
TRACE
Toggles the packet trace flag.
This command enables packet tracing. A GET operation shows a
timeout on a file transfer read request.
Table of Contents
If the network is available, you can install it directly via yum.
You can also download the rpm package first and then install it, download at http://rpmfind.net/linux/rpm2html/search.php?query=tftp-server
After installation, you can find an additional in.tftpd file in the /usr/sbin directory.
2 Configuration
in.tftpd is managed through the xinetd service. /etc/xinetd.conf stores the default configuration of all services managed by xinetd, and also the default configuration of tftpd.
Add the tftp server configuration to the /etc/xinetd.d/tftp file. The configuration specified in this file will override the configuration in the /etc/xinetd.conf file, and the default configuration will be used if no configuration is specified.
3 Start
Create a file directory and modify the file directory access rights
Set the boot self-start, and then start the service.
4 Testing
The tftp client uploads files via the put command and downloads files via the get command, but does not support list file server file and directory listings, nor does it support deleting files
All commands supported by tftp.
Test file upload and download.
5 Principles
TFTP is known as Trivial File Transfer Protocol in English and Simple File Transfer Protocol in Chinese. It provides uncomplicated and low overhead file transfer service. The port number is 69. based on UDP protocol.
2 TFTP Message Types
When TFTP clients send read request and write request messages, the destination port is 69, while Data, Acknowledgement, and Error do not use port 69, they use random ports 1024~5000.
Different operating systems have different port numbers, Linux uses 32768~61000, Windows uses 1025~5000
