Virtual Private Networks, Second Edition

SSH Components

The SSH software is comprised of a small suite of utilities that perform different functions. We’re not going to give you an overview of every feature of these utilities. Instead, we’re going to look at functions and parameters that you should know in order to operate an SSH VPN—both those you should use and those you might be better off not using. For other functionality, we suggest checking the manpages for each of these tools.

sshd

The SSH server daemon is called sshd. As shown in Section 8.2, it’s normally started from an rc file. When launched, it generates the first instance of the server key pair. Because of this, it’s typically not recommended that you start sshd from inetd, because inetd will launch it each time somebody makes a connection. This server key generation adds additional time to the login, sometimes on the order of tens of seconds, depending upon the speed of your machine, its load, and the size of the server key you choose. In some cases this delay will be unacceptable, or at the very least annoying.

sshd has a configuration file called /etc/sshd_config, which lets you set a number of default runtime and security parameters, including port, server key bits, and the types of authentication allowed.

Useful sshd parameters for our purposes

No parameters are normally needed to launch the SSH daemon, but there are a few that can be useful in making modifications.

-b bits

You can set the length of the server key with this option. The default server key ...