Limiting Connections to Manage Resources
Updated: August 22, 2005
Applies To: Windows Server 2003, Windows Server 2003 with SP1
Connection limits restrict the number of simultaneous connections to your Web sites and your Web server. If the number of connections reaches the maximum allotted, all subsequent connection attempts return an error and then are disconnected.
By limiting connections, you can conserve bandwidth for other uses, such as e-mail servers, news servers, or another Web site running on the same installation. Limiting connections also conserves memory and protects against malicious attacks designed to overload your Web server with thousands of client requests.
To determine whether you need to limit connections, use System Monitor to log the Current Connections, Maximum Connections, and Total Connection Attempts counters on the Web Service and FTP Service objects. Continue logging until you have a good sense of the normal range; typically, logging can take several days to a week or more and must be repeated at regular intervals. For more information about performance logging, see Enabling Logging and Analyzing Log Files.
You can establish global WWW service or FTP service connection limits for all Web and FTP sites, or you can establish connection limits on individual Web or FTP sites. IIS checks for a global connection limit before checking for connection limits on individual sites. If the global connection limit is exceeded, IIS returns error message 403.9 (Forbidden - Too Many Users) regardless of the connection limit set for individual sites. (You can customize the connection limit error message in IIS 5.0; however, IIS 6.0 does not offer that option.) For information about limiting connections for the WWW service, the FTP service, a Web site, or an FTP site, see Limiting Connections.
Another way to limit connections to your Web server is through bandwidth throttling. For information about using this feature, see Throttling Bandwidth to Manage Service Availability. For a list of counters related to performance, see IIS 6.0 Performance Counters. For information about connection timeouts, see Setting Connection Timeouts to Save Resources.