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I'm running a Ubuntu 16 based distro on a device, and get no response to ssh requests on port 22 (I am sniffing with tcpdump on the device, and can see the ssh request coming in, but nothing is sent back). When I reconfigure the server to use a custom port, everything works. This reproduces over a modem ppp link in a closed APN (there are no such issues over ethernet). Other devices in this network have no issues with ssh on port 22.

Any ideas on what could the issue be?

user907323
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    No response to the `SYN` packets when you sniff? That usually means dropped packages (iptables/firewall). Can you ssh from the same device? `ssh localhost`. – Eduardo Trápani Apr 03 '20 at 14:27
  • yes, `ssh localhost` works.But thanks to your pointing in the direction of iptables I realized that I myself blocked the ssh port a long time ago and forgot all about it! – user907323 Apr 03 '20 at 14:43

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Seems like a firewall thing, please try this:

sudo ufw allow 22/tcp
MRK
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