Re: SSH forwarding Connection State

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On Mon, 21 Aug 2023, Jeremy Guthrie wrote:

> We have an issue where we’re using SuSE provided OpenSSH 8.4 and we
> have an application using Local Port Forwarding where TCP state does
> not appear to be working right.
> In our problem, we have a separate Linux box app server[]
> using a TCP forward listening on another box[],
> let’s say port 8000. That port 8000 forward is through another
> system( that goes to the actual forwarded host fo
> on port 80. Hopefully that makes sense? :)
> The problem itself: 1. sends a TCP RST to the
> for the forwarded connection. 2. The connection needing to be close
> appears to get to the host (as we would expect) but
> it doesn’t send an RST, it sends an FIN to 3. The
> host sends and ACK but no FIN leaving the in
> the FIN_WAIT2 state. Since SSH itself hasn’t closed, this connection
> stays in this state.
> We have the vendor of the software pushing back that because their
> host sent an RST, SSH should as part of its forward also
> be sending an RST.
> Any thoughts on this behavior? This started a few months ago and we
> aren’t sure of the exact change that may have caused it to crop up.

SSH doesn't attempt to exactly mirror the TCP connection state-machine
but rather roughly approximate graceful half/full close semantics.
AFAIK the SSH channel protocol (RFC4254) offers no way to pass a RST
through a forwarding.

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