When a Web browser retrieves a page from a Web server, the two computers follow several steps:

1. The browser looks up the server's address using a Domain Name Server (DNS) query.
2. The browser and the server establish a network connection.
3. The browser sends an HTTP request across the Internet to the server.
4. The server retrieves the requested page from its file system (or memory cache) and sends it to the browser.
5. The data travels back across the Net to the browser.

The time required for each of these steps is addressed in the Performance Measures table of your Server Check Pro results.

Step (1), the time required to lookup your server's address, is shown by the "DNS Lookup" line. If the DNS system is working correctly this time is rarely a significant portion of the overall time required to deliver a Web page.

If your server's DNS Lookup time is large this probably indicates a problem on our end of the connection, or in the DNS system in general. A long lookup time usually indicates that we didn't find your server's address in our local DNS server and had to query other DNS servers to find it. You might see this behavior if your domain name is new. Remember that it can take several days before a new domain name has circulated through the Internet's DNS system.

Also note that the DNS system sometimes has problems. The system had a major outage on 17 July 1997 which made an estimated 35% of the Net unavailable. The ripple effects of this crash lasted for several days as "non-existent host/domain" messages circulated through the system.

Step (2), the time required to establish a network connection, is shown by the "Connection Time" line. Long connection times can be due to a configuration problem in your server or to large number of users accessing your server at the same time. Possible configuration problems include:

• Your server's TCP listen queue may be set too small. This is often a problem on older versions of UNIX. The steps needed to change this parameter depend on the particular variant of UNIX used by your server and are too complex to cover here.
• Your Web server software may not be configured to support enough connections. The steps needed to change this depend on your Web server. For Apache this is set by the MaxClients server directive. This value is set to 150 by default, meaning that 150 users can be connected to your server at the same time.

We don't directly measure steps (3) and (5), the time required for data to travel across the Internet. However, we estimate this by measuring the "Host Ping" time for communications with your server. Each time we test your server we also "ping" it by measuring the round trip time for a small packet of information to travel between our computer and your server.

This ping response is generated by the network driver on your computer, rather than the Web server. HTTP responses will be affected by the load on your Web server, but pings will not. The ping time therefore gives an idea of the network performance independent of the Web server's performance.

The "Host Ping" line shows this round trip time. A high host ping time could be due to a slow network connect or to heavy traffic on the network.

Step (4), the time required to retrieve the requested file and send it over the Net, is indicated by the "Download Time". We show this time for a notional 10 kilobyte file to allow a better comparison of your server's performance with other servers.

Long Download Times can be due to resource problems within your Web server. Possible causes include:

• Your server's CPU may be overloaded.
• Your server may not have enough RAM.
• Your server's hard drive may have a long access time.
• Your server may not be caching frequently requested pages in memory.
• A large number of requests for unique files may be causing your server to repeatedly access the hard drive.
• Your Web pages may be generated by CGI scripts which take time to execute or require disk access.
• Your Web pages may include Server Side Includes which require disk access.

We assign your server an Overall Grade based on your Download Time. We compare your server's 10k Download Time to the statistical distribution of the same data for all other servers tested by our robot. Your grade will be as follows:

• Excellent - Your server performed better than 80% of the servers we have tested.
• Very Good - Your server performed better than 60% of the servers we have tested.
• Good - Your server performed better than 40% of the servers we have tested.
• Fair - Your server performed better than 20% of the servers we have tested.
• Poor - Your server ranked in the bottom 20% of servers we have tested.