Recommended Registry key configuration to thwart DoS attacks   IMPORTANT NOTE:  Never assume the directory structures exist in your system as written in the document.  Never blindly follow security instructions -- read, review, compare, apply as it fits your system. Caution Incorrectly editing the registry may severely damage your system. Before making changes to the registry, you should back up any valued data on the computer. You can also use the Last Known Good Configuration startup option if you encounter problems after manual changes have been applied. The following registry key settings can be implemented to enable protection against DoS attacks: hkey_local_machine \system \currentcontrolset \services \tcpip \parameters \synattackprotect=1 REG_DWORD hkey_local_machine \system \currentcontrolset \services \tcpip \parameters \tcpmaxconnectresponseretransmissions=2 REG_DWORD hkey_local_machine \system \currentcontrolset \services \tcpip \parameters \tcpmaxdataretransmissions=3 REG_DWORD hkey_local_machine \system \currentcontrolset \services \tcpip \parameters \enablepmtudiscovery=0 REG_DWORD Microsoft Knowledge Base Articles The following Microsoft Knowledge Base articles will also help you protect your network from malicious attacks: Internet Server Unavailable Because of Malicious SYN Attacks This article reveals a global key in the Windows NT registry designed to protect against SYN attacks. TCP/IP & NBT Configuration Parameters for Windows NT and Windows 2000 This article does not relate registry changes to network protection, but explains why the different registry keys are used. HOW TO: Harden the TCP/IP Stack Against Denial of Service Attacks in Windows 2000 HOW TO: Harden the TCP/IP Stack Against Denial of Service Attacks in Windows Server 2003 IMPORTANT NOTE:  This document and all linked document is being provided as a good will gesture to the Parallels H-Sphere community and to others who may benefit from its use.  Dynamic Net, Inc. makes no representations implied or explicit as to their value or warranty. Dynamic Net, Inc. will not be held liable for any damage resulting in the application of the steps and procedures noted.  If you feel uncomfortable at all about doing any of the steps, make a complete system backup and hire a third party like We Manage Servers to do the work for you.