AN2675

IAP using TFTP

7/24

Figure 4.

TFTP packets

The mode field contains the string "netascii", "octet", or "mail" that are the modes defined in

the protocol. Octet mode is used to transfer a file that is in the 8-bit format of the machine

from which the file is being transferred.

2.2

DHCP protocol overview

DHCP is a protocol used by networked computers (clients) to obtain IP addresses and other

parameters such as the default gateway, subnet mask, and a name of a boot file from a

DHCP server. It facilitates access to a network because these settings would otherwise

have to be made manually for the client to participate in the network.

DHCP operations fall into four basic phases. These phases are DHCP Discovery, DHCP

Offers, DHCP Requests and DHCP Acknowledgment.

The Client-Server DHCP interaction is described below:

●

The client broadcasts a DHCP DISCOVER message on its local physical subnet.

●

When a DHCP server receives a DHCP DISCOVER, it reserves an IP address for the

client and send a DHCP OFFER message across the network to the client.

●

When the client, in our case it is the STR912 board, receives a DHCP OFFER, it must

tell all the other DHCP servers that it has accepted an offer. To do this, the client

broadcasts a DHCP REQUEST message that could contain the call for extra

information.

●

When the DHCP server receives the DHCP REQUEST message from the client, it

initiates the final phase of the configuration process. This acknowledgement phase

involves sending a DHCP ACK packet to the client.

2 bytes

String

1 byte

String

1 byte

Opcode

File name

0

Mode

0

Opcode Block#

Data

2 bytes

2 bytes

n bytes

2 bytes

2 bytes

Opcode Block#

2 bytes

2 bytes

String

1 byte

Opcode

Error

code

Error

message

0

RRQ/WRQ packet

Data packet

ACK packet

Error packet