What if two computers send a UDP packet to one computer on the same port? How does the computer distinguish between the two packets?
Example:

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 ( 128.9.0.32, 1184 )->( 128.10.2.3, 53 ) and
 ( 128.2.254.139, 1184 )- > ( 128.10.2.3, 53)

In UDP level the datagrams will have the same identifier because the identifier in UDP is the ports numbers. (1184,53)?
It depends on what you mean by "distinguish."

In general, are they handled the same way at Layer 4? Certainly. Any host sending to the same target host at the same port should get the same response at that level. However, assuming that UDP is built on top of IP (Layer 3), the source address for the UDP packets from two different hosts will be present and different. Thus the packets are distinguishable.

In addition, there are probably other headers and protocols present that would further distinguish the packets.

This was first published in April 2003

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