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Chapter 10. Security

10.2.1. ssh

If you need to connect directly to your server and login from a remote system belonging to you, we strongly encourage you to use ssh instead of

telnet. In addition to UNIX and Linux systems, ssh client software is now also available for Windows and Macintosh systems. (See the section

below.)

If you do not have any reason to allow remote access, we suggest you set this to No access.

ssh (secure shell)

ssh (secure shell) provides a secure, encrypted way to login to a remote machine across a network or to copy ﬁles from a local machine to a

server. Many people do not realize that many programs such as telnet and ftp transmit your password in plain, unencrypted text across your

network or the Internet. ssh and its companion program scp provide a secure way to login or copy ﬁles. The ssh protocol was originally invented

by SSH Communications Security which sells commercial ssh servers, clients, and other related products. The protocol itself has two versions -

SSH1 and SSH2 - both of which are supported by most clients and servers today. For more information about SSH Communications Security

and its commercial products, visit http://www.ssh.com/.

OpenSSH, included with the SME Server V5 with ServiceLink, is a free version of the ssh tools and protocol. The server provides the ssh client

programs as well as an ssh server daemon and supports both the SSH1 and SSH2 protocols. For more information about OpenSSH, visit

http://www.openssh.com/ (http://www.openssh.com/).

Once ssh is enabled, you should be able to connect to your server simply by launching the ssh client on your remote system and ensuring that it is

pointed to the external domain name or IP address for your server. In the default conﬁguration, you should next be prompted for your user name.

After you enter admin and your administrative password, you will be in the server console. From here you can change the server conﬁguration,

access the server manager through a text browser or perform other server console tasks.

If you do enable ssh access, you have two additional conﬁguration options:

• Allow administrative command line access over ssh - This allows someone to connect to your server and login as "root" with the administrative

password. The user would then have full access to the underlying operating system. This can be useful if someone is providing remote support for

your system, but in most cases we recommend setting this to No.

• Allow ssh using standard passwords - If you choose Yes (the default), users will be able to connect to the server using a standard user name and

password. This may be a concern from a security point of view, in that someone wishing to break into your system could connect to your ssh

server and repeatedly enter user names and passwords in an attempt to ﬁnd a valid combination. A more secure way to allow ssh access is called

RSA Authentication and involves the copying of an ssh key from the client to the server. This method is supported by your server, but is beyond

the scope of this user guide and will eventually be covered by additional documentation on the e-smith.org web site.

Note: By default, only two user names can be used to login remotely to the server: admin (to access the server console) and root (to use the Linux

shell). Regular users are not permitted to login to the server itself. If you give another user the ability to login remotely to the server, you will need

to access the underlying Linux operating system and manually change the user’s shell in /etc/passwd.

10.2.1.1. ssh clients for Windows and Macintosh systems

A number of different free software programs provide ssh clients for use in a Windows or Macintosh environment. Several are extensions of existing

telnet programs that include ssh functionality. Two different lists of known clients can be found online at http://www.openssh.com/windows.html

(http://www.openssh.com/windows.html) and http://www.freessh.org/.

A commercial ssh client is available from SSH Communications Security at: http://www.ssh.com/products/ssh/download.html

(http://www.ssh.com/products/ssh/download.html). Note that the client is free for evaluation, academic and certain non-commercial uses.

10.2.2. PPTP

The Point-to-Point Tunnelling Protocol (PPTP) is used to create client-to-server Virtual Private Networks (VPNs) and was developed by the PPTP

Forum, an industry group which included Microsoft and several other companies. A VPN is a private network of computers that uses the public

Internet to connect some nodes. PPTP allows users to connect to their corporate networks across the Internet.

Microsoft’s PPTP implementation is widely used in the Windows world to provide remote access across the Internet. If you have a remote Windows

system (for instance, a laptop or a home computer) that has access to the Internet, you can also access the information stored on your server.

If you wish to enable VPN access, you must decide how many individual PPTP clients you will allow to connect to your server simultaneously, and

enter that number here. The simplest method is to enter the total number of remote PPTP clients in your organization. Alternatively, if you have a

slow connection to the Internet and do not want all of those PPTP clients to connect at the same time, you can enter a lower number here. For

instance, if you have ﬁve users who from time to time use PPTP to connect remotely, entering 5 here would allow all of them to connect at any time.

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