TFTP Protocol - bintec-Dm 765-I

TFTP Protocol

bintec-Dm 765-I

bintec elmeg

Manual

TFTP Protocol 1

Legal Notice

Warranty

This publication is subject to change.

bintec offers no warranty whatsoever for information contained in this manual.

bintec is not liable for any direct, indirect, collateral, consequential or any other damage connected to the delivery,

supply or use of this manual.

Manual bintec elmeg

2 TFTP Protocol

Table of Contents

Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 TFTP Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Detailing a TFTP Session . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2.1 Fundamental Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2.2 Initializing a transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2.3 Types of TFTP Packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.4 Normal Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.5 Premature Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Chapter 2 TFTP Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Accessing the TFTP Configuration Menu . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Configuration menu commands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2.1 ? (HELP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2.2 NO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2.3 SERVER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2.4 EXIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Chapter 3 TFTP Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.1 Accessing the TFTP Monitoring Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.2 TFTP Monitoring Menu Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.2.1 Del . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.2.2 Dir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.2.3 Get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.2.4 Put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.2.5 Syst. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.2.6 Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Chapter 4 Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.1 Loading the code and the configuration file. . . . . . . . . . . . . . . . . . . . . . . . 11

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Table of Contents

TFTP Protocol i

Table of Contents bintec elmeg

ii TFTP Protocol

Chapter 1 Introduction

1.1 TFTP Protocol

The TFTP (Trivial File Transfer Protocol) is a protocol used to transfer files between various machines connected

through a communications network.

TFTP is a very simple protocol, similar to a basic version of FTP (File Transfer Protocol), which is defined in RFC

1350. TFTP is implemented over a non-reliable, non-orientated to connection communications service. TFTP func-

tionality mainly consists in a client reading or writing a file (occasionally an electronic mail) from a remote server.

The main characteristics distinguishing this from FTP are as follows:

• Uses UDP (port 69) as the transport protocol (unlike FTP which uses TCP port 21).

• It cannot list the content of the remote directories, and therefore needs the client to know the complete route in the

server and the name of the files in order to transfer them.

• There are no authentication or encryption mechanisms, so it should be used over secure network paths (private

networks, local networks, etc.).

• It supports three different transfer modes, "netascii", "octet" and "mail". The first two correspond to the “ascii” and

“image” (binary) from the FTP protocol.

This protocol is often used to transfer small files between PCs in a network, such as when an X Window terminal or

any other lite client boots from a network server. A common use of this protocol is the transfer of booting programs.

1.2 Detailing a TFTP Session

As TFTP uses UDP, there is no formal definition for session, client and server. However each file transferred through

TFTP constitutes an independent exchange of packets, and there is an informal client-server relationship between

the machine initiating the communication and that responding.

1.2.1 Fundamental Characteristics

Any file transfer begins with a client requesting a file reading or writing.

If the server accepts the request, the file is sent in fixed length blocks of 512 bytes. Each data packet contains one of

these blocks and has a block number, beginning the transfer with block number 1. The data packets must be ac-

knowledged, so in the absence of machine failure, the file is correctly transferred. The acknowledgment packet indic-

ates the block number it’s acknowledging. Until acknowledgement for a block has been received, the next one is not

sent.

A data packet containing fewer than 512 bytes indicates the end of the transmission.

If a packet is lost during transmission, the receiver will timeout and must retransmit the last transmitted packet (data

or acknowledgement). This causes the sender of the lost packet to retransmit this said packet. Please note that both

the client as well as the server use timeouts.

Three types of events cause errors:

• When it is not possible to accept a transfer request (file not found, permit violation).

• When an incorrectly formatted packet is received.

• When access to a resource is lost (the disk is full) in the middle of a transfer.

Errors cause the termination of the transfer. Sending an error packet indicates an error. This packet is neither ac-

knowledged nor retransmitted, so the other end of the connection may not ever receive this.

1.2.2 Initializing a transfer

A transfer is initialized by a client sending a request (WRQ to request to write or RRQ to request to read) and a posit-

ive reply from the server received by the said client. This positive reply can be an acknowledgement packet – for

write – or the first data packet –for read--. The acknowledgement packet for write takes block number 0. If the re-

sponse to a request is an error packet, the request has been denied.

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TFTP Protocol 1

1.2.3 Types of TFTP Packets

TFTP uses 5 types of packets:

Type Acronym Operation

1 RRQ Read request

2 WRQ Write request

3 DATA Data packet

4 ACK Acknowledgement packet

5 ERR Error packet

1.2.3.1 RRQ and WRQ Packets

These take the following format:

Type File name

Type: 1 for RRQ and 2 for WRQ.

File name: Arbitrary length string.

1.2.3.2 DATA Packets

These take the following format:

Type Block number Data

Type: 3

Block number: 1 for the first block and this progressively increases up to 65535 and consequently zeroizes again.

Data: from 0 to 512 bytes with a file block that is read or write. If this is precisely 512 bytes, it is NOT the last data

packet. If it is from 0 to 511 bytes then this indicates the end of the transfer.

1.2.3.3 ACK Packet

These take the following format:

Type Block number

Type: 4

Block number: Indicates the block number being acknowledged. If this is zero is this an acknowledgement for a

write request.

All packets that are not ERR must be acknowledged. Sending a data packet is an ACK acknowledgement for

the previous block.

Therefore WRQ or DATA packets are acknowledged by ACK or ERROR packets, while RRQ and ACK packets

are acknowledged by DATA or ERR packets.

1.2.3.4 ERR Packets

These take the following format:

Type Error code Message

Type: 5

Error Code: Indicates the nature of the error. The following table explains the meaning of each value:

Value Meaning

0 Not defined

1 File not found

2 Access violation

3 Disk full

4 Illegal TFTP operation

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2 TFTP Protocol

5 Unknown transfer mode

6 File already exists

7 No such user

Message: Undetermined length string to extend information on an error should this be necessary.

1.2.4 Normal Termination

The end of a transfer is indicated with a DATA packet of 0 to 511 bytes. This packet must be acknowledged with an

ACK packet (like all other DATA packets).

The machine acknowledging the last DATA packet can close its side of the communication after sending the ACK,

however it is more normal to wait a while in order to retransmit the last ACK should it get lost. This situation is detec-

ted if the machine receives the last DATA packet again.

The machine sending the last DATA packet must wait until it has received the ACK or stop after a determined period

of time. If it stops, it will terminate its side of the communication without knowing if the transfer has been completed

or not (depending if it was the last ACK or the last DATA packet respectively, which was lost).

1.2.5 Premature Termination

If a request could not be accepted or an error has occurred in the middle of a transfer, then an error packet is sent

and the communication terminated. This packet is not acknowledged nor retransmitted which means it may never

reach its destination.

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TFTP Protocol 3

Chapter 2 TFTP Configuration

2.1 Accessing the TFTP Configuration Menu

In order to access the TFTP configuration menu, use the FEATURE TFTP command found in the main configuration

menu.

Example:

*config

Config>feature tftp

-- TFTP user configuration --

TFTP config>

2.2 Configuration menu commands

This section describes the TFTP configuration menu commands.

The following table summarizes the commands available in the TFTP configuration menu. These commands are

more fully explained further on.

Command Function

? (HELP) Displays the configuration commands or their options.

NO Configures the parameters with their default values.

SERVER Configures the TFTP server parameters.

EXIT Exits the TFTP configuration menu.

2.2.1 ? (HELP)

Displays the available configuration commands or their options.

Syntax:

TFTP config>?

Example:

TFTP config>?

no Negate a command or set its defaults

server Configures TFTP server parameters

exit Exit to parent menu

TFTP config>

2.2.2 NO

Configures the parameters with their default values.

Syntax:

TFTP config>no ?

server Configures TFTP server parameters

enable Enables TFTP server

file-system File system to use for TFTP

port Port used to receive TFTP requests

Example:

Disables the TFTP server.

TFTP config>no server enable

TFTP config>

Example:

Sets the file system used by the TFTP server to its default value.

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4 TFTP Protocol

TFTP config>no server file-system

TFTP config>

2.2.3 SERVER

Configures the TFTP server parameters.

Syntax:

TFTP config>server ?

enable Enables TFTP server

file-system File system to use for TFTP

port Port used to receive TFTP requests

2.2.3.1 SERVER ENABLE

Enables the TFTP server. Once enabled, the device responds to file read and write requests.

Example:

TFTP config>server enable

TFTP config>

2.2.3.2 SERVER FILE-SYSTEM

Configures the file system used by the TFTP server to its default value. The TFTP server reads or writes files in the

configured file system.

Syntax:

TFTP config>server file-system ?

NUL Default file system when a system has not been loaded

TST Checks that the FTP is operating correctly

MEM Temporary buffer

DSK Handles the disk.The code and configurations are stored here

FCO Handles the code Flash memory

FDA Handles the data Flash memory

BIO Handles the BIOS zone.Only the BIOS code files are saved here

SMC Handles the Smart Memory Card

TFTP config>

The available file systems are as follows:

NUL: default file system.

TST: used to check the performance of the protocol.

MEM: temporary buffer.

DSK: disk system. The code and configurations are saved here.

FCO: Flash memory used for the code.

FDA: Flash memory used for data.

BIO: BIOS area. To store BIOS files.

SMC: Smart Card.

Default value: the NUL system is used by default.

2.2.3.3 SERVER-PORT

Configures the port used by the TFTP server to listen to requests.

Syntax:

TFTP config>server port <port>

<0..65535> Port number

Example:

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Configuration for port 150 as the listening port.

TFTP config>server port 150

Default value: port 69 is used by default.

2.2.4 EXIT

Exits the TFTP configuration menu.

Syntax:

TFTP config>exit

Example:

TFTP config>exit

Config>

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6 TFTP Protocol

Chapter 3 TFTP Monitoring

3.1 Accessing the TFTP Monitoring Menu

In order to access the TFTP monitoring menu, use the FEATURE TFTP command found in the main monitoring

menu.

Example:

*monitor

Console Operator

+features tftp

TFTP manager

TFTP+

3.2 TFTP Monitoring Menu Commands

This section describes the TFTP monitoring menu commands. These commands allow you to use the TFTP client.

The following table summarizes the commands available in the TFTP Monitoring Menu:

Command Function

del Deletes the specified file from the device’s active file system.

dir Displays information on the active file system directory.

get Transfers (read) a file stored in a TFTP server to the TFTP client active file sys-

tem.

put Transfers (write) a file from the active file system of the TFTP client to a TFTP

server.

syst Establishes the active file system in the device for the TFTP client.

exit Exits the TFTP Monitoring menu.

3.2.1 Del

Deletes the specified file from the active file system in the device.

Syntax:

TFTP>del <file>

• < file > the complete name (including the extension) of the file which we wish to delete from the active file system

Example:

TFTP>dir

Current file system: DSK

Name Length Attributes

-----------------------------------------

0 ---V--

XXX.BIN 3521280 -----A

XXX.CFG 2463 -----A

IGMP.CFG 1611 -----A

Total: 4 files, 3525354 bytes. 390144 bytes free.

TFTP>del igmp.cfg

File erased

TFTP>

In order to check that the file has effectively been deleted, you can list the files currently found in the active file sys-

tem.

TFTP>dir

Current file system: DSK

Name Length Attributes

-----------------------------------------

0 ---V--

XXX.BIN 3521280 -----A

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XXX.CFG 2463 -----A

Total: 3 files, 3523743 bytes. 392192 bytes free.

TFTP>

3.2.2 Dir

Lists information on the active file system directory on screen.

Syntax:

TFTP>dir

Example:

TFTP>dir

Current file system: DSK

Name Length Attributes

-----------------------------------------

0 ---V--

XXX.BIN 3521280 -----A

XXX.CFG 2463 -----A

IGMP.CFG 1611 -----A

Total: 4 files, 3525354 bytes. 390144 bytes free.

TFTP>

The meaning of the fields that appear is as follows:

• General Information

Current file system Device file system active in the TFTP client.

Total Total number of files in the active file system, total space in bytes occupied by the

said files. The rest is the free space in the active file system.

• Information on the files

Name Complete name of the file.

Length Space in bytes occupied by the file.

Attributes File attributes (R: Read only / H: Hidden / S: System / V: Volume / D: Directory / A:

Archive).

3.2.3 Get

Transfers (read) a file stored in the TFTP server to the TFTP client active file system.

Syntax:

TFTP>get [<vrf>] <server> <source_file> [{<ip> | <ifc>}]

TFTP>get [<vrf>] <server> <source_file> [<destination_file>] [{<ip> | <ifc>}]

• < vrf > This is the name of the VRF used to communicate with the TFTP server in cases where this is located in a

secondary VRF.

• < server > this is the TFTP server IP address from where we wish to transfer the source file.

• < source_file > this is the complete name of the file (including extension and route) that we wish to transfer (read)

from the TFTP server file system.

• < destination_file > this is the complete name of the file (including the extension) where we want to write the ori-

ginal file within the TFTP client active file system.

• < ip > this is the IP address used as source for the TFTP petition.

• < ifc > this is the name of the interface used to get the TFTP petition IP source address.

Example 1:

TFTP>get 10.1.1.1 cfgfiles\XXXsample.cfg XXX.cfg

Receiving XXX.cfg from 10.1.1.1\cfgfiles\XXXsample.cfg...

2463

File successfully received

TFTP>

In order to check that the file has effectively been transferred from the server, you can list the files currently found in

the active disk.

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8 TFTP Protocol

TFTP>dir

Current file system: DSK

Name Length Attributes

-----------------------------------------

0 ---V--

XXX.BIN 3521280 -----A

XXX.CFG 2463 -----A

Total: 3 files, 3523743 bytes. 392192 bytes free.

TFTP>

Example 2:

TFTP>get vrf-3 10.1.1.1 XXX.cfg 10.1.1.51

Receiving XXX.cfg from 10.1.1.1...

2463

File successfully received

TFTP>

3.2.4 Put

Transfers (write) a file from the active file system of the TFTP client to the TFTP server.

Syntax:

TFTP>put [<vrf>] <server> <source_file> [{<ip> | <ifc>}]

TFTP>put [<vrf>] <server> <source_file> [<destination_file>] [{<ip> | <ifc>}]

• < vrf > This is the name of the VRF used to communicate with the TFTP server in cases where this is located in a

secondary VRF.

• < server > TFTP server IP address to which you wish to transfer the source file.

• < source_file > this is the complete name (including the extension) of the file that you want to transfer from the

active file system.

• < destination_file > this is the complete file name (including extension and route) where you want to write the

source file within the TFTP server file system.

• < ip > this is the IP address used as source for the TFTP petition.

• < ifc > this is the name of the interface used to get the TFTP petition IP source address.

Example 1:

TFTP>put 10.1.1.1 XXX.cfg \cfgfiles\XXXsample.cfg

Sending XXX.cfg to 10.1.1.1\\cfgfiles\XXXsample.cfg...

Sending 2463 bytes

2463

File successfully sent

TFTP>

Example 2:

TFTP>put vrf-2 10.1.1.1 XXX.cfg ethernet0/1.11

Sending XXX.cfg to 10.1.1.1...

Sending 2463 bytes

2463

File successfully sent

TFTP>

3.2.5 Syst

Establishes the active file system in the device for the TFTP client.

Syntax:

TFTP >syst <file system>

• < file system > this is the code for the file system name we want to activate.

In order to find out what file systems are available in the device, activate the root file system (NUL) and subsequently

a list of the existing files will appear. An example of this is given below:

TFTP>syst nul

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Current file system set to NUL

TFTP>dir

Current file system: NUL

Name Length Attributes

-----------------------------------------

TST 0 ----D-

MEM 0 ----D-

DSK 0 ----D-

BIO 0 ----D-

Total: 4 files, 0 bytes.

TFTP>

The list of directories that appear corresponds to the manageable file systems in the device. A list showing the most

common file systems in our devices is shown below together with their applications:

BIO BIOS zone. Only the BIOS code files are saved here

DSK Disk. The code and configurations are stored here

FCO Code Flash memory

FDA Data Flash memory

MEM Temporary buffer

NUL Default file system when a system has not been loaded

SMC Smart Memory Card

TST FTP Checking zone

Example:

TFTP>syst fda

Current file system set to FDA

TFTP>

By default the active file system is DSK.

3.2.6 Exit

Exits the TFTP Monitoring menu.

Syntax:

TFTP>exit

Example:

TFTP>exit

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10 TFTP Protocol

[1] Given that DSK is the default file system – where the code and the configuration files for the devices are normally loaded – it won’t be necessary, in

this particular case, to execute a selection operation.

Chapter 4 Example

4.1 Loading the code and the configuration file

Supposing we have the following situation:

We want to remotely download a code release ( newXXX.bin) as well as a new configuration file (newXXX.cfg) for the

router. Both files are stored in a TFTP server, accessible through the device.

The first task is to connect to the router from the local host (e.g. via telnet) and subsequently use the TFTP client the

router has to transfer the required files from the TFTP server.

Once connected to the router (through the console or LAN), access the TFTP clients interface and select the file sys-

tem where we want to load the files, in this case, DSK

Router model XXX 2 8 CPU MPC860 S/N: 403/00122

1 LAN, 3 WAN Lines, 1 ISDN Line

OS software version: 10.5.4-Alfa Feb 16 2005 13:30:43

*monitor

Console Operator

+tftp

TFTP manager

TFTP>syst dsk

Current file system set to DSK

TFTP>

To check we are in the selected file system, execute a listing:

TFTP>dir

Current file system: DSK

Name Length Attributes

-----------------------------------------

0 ---V--

XXX.BIN 3521280 -----A

XXX.CFG 2463 -----A

IGMP.CFG 1611 -----A

Total: 4 files, 3525354 bytes. 390144 bytes free.

TFTP>

Once that is done, begin to download the new code release –newXXX.bin– found in the TFTP server “code” direct-

ory. To do this, execute the following command:

TFTP>get 10.1.1.1 \code\newXXX.bin XXX.bin

Receiving newXXX.bin from 10.1.1.1\\code\newXXX.bin...

3521536

File successfully received

TFTP>

As you can see, we have given the destination file the same name – XXX.bin- as the code file is already in the device

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TFTP Protocol 11

[2] Provided that the name of the active configuration file currently in the device has not been used for the destination file.

(displayed on executing the previous listing). This means the said file will be overwritten. However if the device has

sufficient free space in the file system, we recommend you use a different destination file name and subsequently ac-

tivate this new code release selecting the said file through the set application-active configuration command. This is

a precaution means against situations such as a power cut occurring during the download, the device in this case

would be out of service as the code file will be incomplete.

Note

Whenever possible, we strongly recommend that the new file is saved under a different name, estab-

lishing it as active, and subsequently deleting the old file.

Next we need to download from the configuration file – newXXX.cfg- which can be found in the TFTP server

“cfgfiles” directory. To do this, execute the following command:

TFTP>get 10.1.1.1 \cfgfiles\newXXX.cfg XXX2.cfg

Receiving XXX2.cfg from 10.1.1.1\\cfgfiles\newXXX.cfg...

2463

File successfully received

TFTP>

In this case, we have saved the new configuration file as XXX2.cfg in the active file system (DSK).

We can check that both files have been correctly written to DSK by listing the active file system and checking that the

name and length coincide with the transmitted files:

TFTP>dir

Current file system: DSK

Name Length Attributes

-----------------------------------------

0 ---V--

XXX.CFG 2463 -----A

IGMP.CFG 1611 -----A

XXX.BIN 3521536 -----A

XXX2.CFG 2463 -----A

Total: 5 files, 3528073 bytes. 387072 bytes free.

TFTP>

Please note that in order to activate the new configuration file in the device, you need to inform

the device through

the configuration menu:

TFTP>exit

+ctrl+p

*config

Config>set file-cfg XXX2.cfg

Config>

The last action to carry out is to reboot the device so the new code release and the new configuration activate.

Config>ctrl+p

*load immediate

Are you sure to reload the device(Yes/No)? y

Done

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