Article ID: 896350 - Last Review: July 1, 2010 - Revision: 6.0

Security update 893066 introduces the MaxIcmpHostRoutes registry entry

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INTRODUCTION

Security update 893066 (http://www.microsoft.com/technet/security/bulletin/ms05-019.mspx) introduces the MaxIcmpHostRoutes registry entry.

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Security update 893066 adds the optional, new MaxIcmpHostRoutes registry parameter to all the operating systems that are listed in the "Applies to" section.

The Microsoft TCP/IP stack supports Internet Control Message Protocol (ICMP). This maintenance protocol is specified in RFC 792. ICMP is ordinarily considered part of the Internet layer. ICMP messages are encapsulated within IP datagrams. Therefore, they can be routed throughout a network. ICMP lets host routes be added by sending an ICMP message to the host. The MaxIcmpHostRoutes entry controls the maximum number of such host routes that can coexist at the same time.

By default, the maximum number of coexisting host routes is 10000. After the MaxIcmpHostRoutes entry is added, the maximum number of coexisting routes is value of this entry plus one. The maximum value of the MaxIcmpHostRoutes entry is 2,147,483,646.

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Registry entry specifics

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Entry name	MaxIcmpHostRoutes
Registry subkey	HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
Data type	REG_DWORD (number)
Valid range	0x0 to 7FFFFFFE (0 to 2,147,483,646)
Default value	0x2710 (1000)
Description	This value restricts the number of host routes that can be added to the local IP route table by receiving ICMP Redirect messages. You should not change this value unless the computer must be able to add many host routes by receiving ICMP Redirect messages.

For more information about ICMP, visit the following Microsoft Web site:

http://technet2.microsoft.com/WindowsServer/en/library/823ca085-8b46-4870-a83e-8032637a87c81033.mspx?mfr=true (http://technet2.microsoft.com/WindowsServer/en/library/823ca085-8b46-4870-a83e-8032637a87c81033.mspx?mfr=true)

To view RFC 792, visit the following Internet Society Web site:

http://www.rfc-editor.org/rfc/rfc792.txt (http://www.rfc-editor.org/rfc/rfc792.txt)

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Note This is a "FAST PUBLISH" article created directly from within the Microsoft support organization. The information contained herein is provided as-is in response to emerging issues. As a result of the speed in making it available, the materials may include typographical errors and may be revised at any time without notice. See Terms of Use (http://go.microsoft.com/fwlink/?LinkId=151500) for other considerations.

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