Namely the sshd configuration (controlled by /etc/ssh/sshd_config) should employ a "default deny" stance for allowing SSH tunnels. SSH tunneling can open up your system to many security problems if some thought and sane defaults are not put in place. Another thing to note: while the examples shown use localhost tunnels can also be bound to public interfaces providing another avenue of abuse. By providing a channel that can effectively bypass normal firewall protections it is easy for an unscrupulous user to setup back-channels that are not monitored. While tunnels can be useful as evidenced in how Aspera uses them it should be apparent that they also pose security problems. The concepts are the same but relevant depending on access to the system. There is a corresponding -Roption to setup sockets on the remote host as well. It should also be noted the -L option is what sets up the local socket. The service that needs to use the tunnel can now make connections to the local socket (on port 50000). $ ssh -L 50000:localhost:40001 will know the tunnel works by using netstat and filtering out for port 50000 on the side that created the tunnel: The client service (like a SOAP consumer) instead of using remote_IP: 40001 will attempt connections to localhost: 50000.Īs shown in the above example this tunnel is done using the example ports like so:.The server end does not require any changes to accommodate this.On the remote end the tunnel will funnel traffic to the remote end's port 40001. Port 50000 will be used for uniqueness and clarity of example. On the client side: Since traffic to the localhost does not pass through the unsecured network ssh is used to connect to the remote/ server host via port 22 and a tunnel is setup bound to a local port.This is done automatically in Console 1.5 and above but in essence what happens is the following: This SOAPdata is not natively encrypted so transmission over an insecure medium is done through the use of tunnels. Central provides SOAP services on port 40001. The most common use of SSH tunnels with Aspera software is the Aspera Central service. Tunnels secure data but also allow the user to "punch holes" in networks that can be used to access restricted services. These new sockets replace the the old sockets one would normally use. The mechanism ssh uses to provide access to this is to create new sockets at each end of the tunnel which an application can use to access the TCP service. ssh sets up an encrypted path between two systems - a connection to the remote server that takes in data on one end and ssh encrypts it as it travels over an unprotected medium to the other side. In a way a tunnel is exactly what the name implies. This combination of IP: port is called a socket and represents a network endpoint of some type (local or remote) this info is important later. In a normal connection a server connects to an IP address and the port the service is running on. To answer this question we need to understand what we are trying to achieve. What does this command do and how does a tunnel work? Tunnel Basics $ ssh -L 40001:localhost:40001 the password has been entered for the someuseruser on the somehost server the tunnel is setup. From any command window a user can use a command like the following to create the tunnel: For simplicity, these examples will assume a linux server, but the examples can easily be ported to a Windows system as well. ![]() While tunnel use in Aspera software is done automatically in Console 1.5 and above, it is useful to know these concepts for earlier Console deployments, and to understand the technologies deployed on your network. This article will also describe the security implications of running tunnels and how to shut them down. This tutorial will provide the basic understanding of SSH tunnels needed to setup a tunnel. Along with core protocol functionality, ssh can be used to provide secure communication for other TCP traffic, like that used by Aspera Central's SOAP service. Aspera heavily leverages the Secure SHell ( ssh) technology, developed to access Unix and Linux systems, to provide secure communications and authentication for session initiation.
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