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ncat cannot listen to multiple UDP clients #1223

pronebird opened this issue May 23, 2018 · 2 comments

ncat cannot listen to multiple UDP clients #1223

pronebird opened this issue May 23, 2018 · 2 comments


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pronebird commented May 23, 2018


I have a simple program that sends a message to UDP port. I'd like to use ncat to monitor it. The program itself opens a new UDP connection each time it sends a new message, so it seems that ncat is not able to handle multiple clients at the same time since I only see the message received from the very first client and only once.

ncat -ul 1234

After showing the first message, ncat hangs. If I hit enter it prints out:

Ncat: An existing connection was forcibly closed by the remote host

In case of macOS and netcat everything works fine with a very small timeout, i.e: nc -ul 1234 -w 1, same trick doesn't work with ncat though.

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si74 commented Sep 29, 2020

I'm experiencing the same issue on Ubuntu 20.04

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dmiller-nmap commented Oct 10, 2022

This has been expected behavior. Traditional and OpenBSD netcats also have this limitation. However, I have updated Ncat to be able to support multiple UDP clients with the --keep-open or -k option. The commit message will close this issue when it is synced.

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