OOB packets and port forwarding

[Damien Miller]

George Faber wrote:
> I have an application that uses a 1-byte OOB packet
> for a heartbeat signal. It appears that openssh blocks
> these packets when I use it to forward to a remote
> port.
> The application works fine when connected to the
> server
> using the port forward, but all heartbeat packets are
> stripped out from the socket data.
> 
> Is this intentional? Is it a bug? I've tried several
> versions of openssh without success.
> 
> Any hints or help will be very appreciated.

By OOB data, I presume you mean TCP segments with URG flag set?

The SSH protocol does not have the means to preserve these across
a port forwarding. It may be possible to add, but it would require a
protocol extension, perhaps using SSH_MSG_CHANNEL_EXTENDED_DATA.

-d