SSH connection over port 443 fails (kex_exchange_identification: Connection closed by remote host)

[Armen Arsenyan]

Hi Trevor / Serveo Team,

According to the documentation, connection on port 443 is supported for environments where port 22 is blocked:
ssh -p 443 -R 80:localhost:8888 serveo.net

However, when attempting to connect over port 443, the connection immediately drops during protocol identification, even with an SSH key registered in the Serveo Console.

Test details:
1. Generated and added an SSH key to the Serveo Console.
2. Tested from Windows 11 (OpenSSH) and OpenWrt (Dropbear / dbclient) in an unrestricted network environment outside filtered ISPs.
3. Standard SSH connection over port 22 works perfectly with the same key and custom subdomains.

Log output:
PS C:\Users\user> ssh -p 443 -i "$env:USERPROFILE\.ssh\id_serveo_win" -N -R myalias.serveousercontent.com:22:localhost:22 serveo.net
Connection closed by 37.27.37.254 port 443

Detailed verbose log (ssh -v -p 443):
debug1: Connecting to serveo.net [37.27.37.254] port 443.
debug1: Connection established.
...
debug1: Local version string SSH-2.0-OpenSSH_for_Windows_9.5
kex_exchange_identification: Connection closed by remote host
Connection closed by 37.27.37.254 port 443

Could you please clarify if raw SSH tunneling on port 443 is currently supported, or if port 443 is now reserved exclusively for HTTPS and WireGuard traffic?

Thanks!