Filtering by Specific IP Addresses May Not Be Effective

• Microsoft Proxy Server versions 1.0 and 2.0

SYMPTOMS

Enable filtering for Web Proxy and Winsock Proxy services by specified IP address may not work effectively.

CAUSE

Filtering by specified IP address may not work effectively because several IP address may answer for a given domain name. If you pick one address, you will miss the other addresses that mirror the same server content.

Also in some networks, IP addresses may be dynamically assigned by using Bootstrap Protocol (BOOTP) or Dynamic Host Control Protocol (DHCP) services. When BOOTP and DHCP are in use, the remote server's IP address may change.

WORKAROUND

Apply filtering based on DNS Domain names for specific sites.

MORE INFORMATION

If you manage a large private network that uses TCP/IP but does not connect to the Internet, you may find it easier to precisely filter access by entering specific IP addresses.

Although DNS filtering is easier to manage and generally preferred where available, listing individual IP addresses for filtering is a valid option where DNS naming services are not managed on your network, and your private network uses static IP addressing.