SME Server:Documentation:Administration Manual:Appendix

SME Manual Appendix

The following Appendix pages are included for your information.

Appendix A. Introduction to the Ethernet Local Area Network (LAN)

A local area network (LAN) is the system of wires and other hardware that connects the computers within your office and allows them to communicate with one another. An ethernet LAN is the most common type. Ethernet refers both to a kind of connection and to a protocol for how Internet data packets travel around your network.

The hub, a common component of an ethernet, serves as a point of interface between computers on the network. Each computer on your network is connected to the hub using an ethernet network cable. Different hubs operate at different speeds: slower hubs, operating at 10 MB/sec, are suitable for small networks; faster hubs, operating at 100 MB/sec, are suitable for larger networks. Switching 10/100 MB hubs can operate at either speed, and provide a good way to upgrade your network gradually.

An ethernet adapter, also called an ethernet card or network interface card (NIC), connects each computer to the ethernet LAN. An server with a dedicated Internet connection requires two ethernet adapters; one connects it to your LAN and the other connects it to the external network that leads to your ISP. If your server connects to your ISP using a modem or ISDN adapter, it only requires one ethernet adapter. A router ensures that Internet data packets (e.g. e-mail, web page information, etc.) reach the appropriate computers on your network. Routing is one of the functions performed by the server in server and gateway mode.

Allowing a third party, such as a systems integrator or networking company, to install your ethernet can be a good idea. It can help you select, procure and install the appropriate ethernet adapters, hub and cables. There are also various how-to guides available in bookstores if you are committed to installing it on your own.

Appendix B. Dynamic DNS Services

If your IP address is assigned dynamically, you may find it helpful to use a dynamic DNS service. A dynamic DNS service provides you with an automated way to notify them whenever your IP address changes so that they can immediately publish new DNS records for your domain. Without dynamic DNS, you would have to contact your ISP to have them change your DNS records, and your web site and other services would be unavailable for several days until the change was processed. You can easily enable the usage of a dynamic DNS service by selecting it on your server console.

A dynamic DNS service can be a great solution when used with a dedicated connection. With a typical dialup connection, your IP address changes much more frequently (possibly every time your server connects) and, because the server only connects intermittently, there is a delay in informing the dynamic DNS service of the change. This means that the risk of misdirected information is much greater with a dialup connection. For this reason, we recommend and support the use of dynamic DNS services only for dedicated connections.

Contribs.org has tested four dynamic DNS services, of which two are free services and two are commercial services: yi.org (free), dyndns.com (commercial), tzo.com (commercial) and dyndns.org (free). For simplicity, we have preprogrammed the server to work with these services (including pre-installing their client software). If you have arranged dynamic IP address assignment from your ISP and you wish to use one of these services, all you need to do is visit the appropriate web site to sign up for service, and enable that particular function in the server console. In pre-configuring the server for this particular service, we in no way interfere with nor prevent you from using another dynamic DNS service if you wish. To do so, however, would require some customized configuration on your part.

Contribs.org has tested the functionality of these services with our software. However, we accept no liability for any breach of service on their part. A failure on the part of your dynamic DNS service can result in your network becoming temporarily unreachable from the Internet. During these times, your e-mail may be undeliverable.

If your IP address is assigned dynamically and you intend to receive all your e-mail directly (rather than having it stored at an ISP and retrieving it via POP or IMAP), but you decide not to use a dynamic DNS service, you should implement multidrop e-mail as your e-mail solution as this will ensure that no e-mail is misdirected to another IP address (See Some important notes on Service list D (multidrop mail) in|Chapter 3.)

Appendix C. Proxy Servers

The server comes with a proxy server called Squid which can proxy the web (HTTP), FTP and Gopher protocols. Proxy servers temporarily store information from the Internet on the hard drive of the server, allowing other users to access it directly from that hard drive. For example, when an employee visits a web page, the web proxy server will store that web page. Subsequent visitors to that web page will read it from your proxy server's hard drive, rather than over the Internet. This slightly reduces the network performance for the first visitor to that web page, but can enhance the performance for subsequent visitors.

Many gateway systems require the use of proxy servers, but with the server it is optional. Networked applications such as web browsers will work perfectly without proxying, due to the IP masquerading capability of the server.

In general, we recommend that proxying be disabled in your network applications. Using the proxy server can benefit the organization if you have a slow Internet connection and you've installed your server software on a fast computer. In this case, reading from the hard drive will be faster than reading from the Internet. Remember, though, that a proxy server benefits the second and subsequent visitors to a site but not the first visitor, so this benefit only applies if your users tend to visit the same sites repeatedly.

A proxy server is generally not appropriate if you have a fast Internet connection and you've installed your server software on a lower- or mid-level computer. In this case, reading from the hard drive of the computer may not be faster than over the Internet. It also offers no benefit to your organization if employees at your site do not tend to visit the same web pages.

Appendix D. Technical Support

If you are having difficulty configuring another vendor's hardware or software, we recommend you refer to the manual or contact the vendor for that product.

The SME Server is open source software, Contribs.org encourages users to freely share copies of our software.

Developers may wish to note that additional documentation, including HOWTO documents and a FAQ, can be found on our development web site - http://wiki.contribs.org/. There are also links there to other web sites relating to the server.