On Thu, May 08, 2008 at 04:16:12PM -0700, arguellodw wrote:
> I'm having a difficult time understanding the difference between these two
> local tunnels. Here is how I see them:

> 1) mymachine: $ ssh 5900:localhost:5900 remotehost
> 2) mymachine: $ ssh 5900:remotehost:5900 remotehost

I assume you mean ssh -L 5900:... in each case.

In the first case, the sshd on the remotehost makes a TCP connection to
localhost:5900, meaning the service receives the connection on the
loopback interface (127.0.0.1).

In the second case, the sshd on the remotehost makes a TCP connection to
remotehost:5900, meaning the service receives the connection on whatever
interface the address of "remotehost" is bound to (typically not loopback).

This matters only if the service is listening on a particular interface
(loopback only for example), or if it has access control rules based on
the source IP of the connections, or if the kernel has firewall rules
that control access in some way.

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