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I'm trying to figure out what I need to send (client) in the NTP request package to retrieve a NTP package from the server. I'm working with the LWIP on Cortex M3, Stellaris LM3S6965
I understand that I will recieve a UDP header and then the NTP protocol with the different timestamps the remove the latency. I probable need to make an UDP header but what do I need to add as data?
wireshark image:
I hope you guys can help me.
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The NTP packet header follows the UDP and IP headers and the physical header specific to the underlying transport network. It consists of a number of 32-bit (four-octet) words, although some fields use multiple words, and others are packed in smaller fields within a word.
After a client is synchronized, it will typically send an NTP request packet to the Server once every 1024 seconds.
NTP is a built-on UDP, where port 123 is used for NTP server communication and NTP clients use port 1023 (for example, a desktop).
NTP packets are relatively small, and without any optional extensions the incoming and outgoing packets are 76 octets in length. This implies that while NTP is a packet reflector, its not normally an amplifier as well, so attackers have preferred to use DNS instead.
The client request packet is the same as the server reply packet - just set the MODE bits in the first word to 3 (Client) to be sure.
Send the whole 48 byte packet to the server, it will reply with the same.
The simplest packet would be 0x1B followed by 47 zeroes. (Version = 3, mode = 3)
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