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TcpMaxPortsExhausted

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

Data type

Range

Default value

REG_DWORD

0x0–0xFFFF

0x5

Description

Determines how many connection requests the system can refuse before TCP/IP initiates SYN flooding attack protection . The system must refuse all connection requests when its reserve of open connection ports runs out. This entry is used only when SYN flooding attack protection is enabled on this server, that is, the value of the SynAttackProtect entry is 1 and the value of the TcpMaxConnectResponseRetransmissions entry is at least 2).

This entry establishes one of three configurable thresholds that, if exceeded, trigger TCP's SYN attack flooding protection feature. Because SYN flooding often consumes all reserved connection ports, TCP interprets an elevated number connection refusals and a depleted port reserve as a symptom of SYN flooding.

The other two thresholds are:

  • The total number of connections in the half-open (SYN-RCVD) state exceeds the value of the TcpMaxHalfOpen entry.

  • The number of connections that remain in the half-open (SYN-RCVD) state even after a connection request has been retransmitted exceeds the value of the TcpMaxHalfOpenRetried entry.

Note Image Note

If the value of this entry is 0, SYN flooding protection is triggered as soon as the backlog of connection ports is consumed.

Windows 2000 does not add this entry to the registry. You can add it by editing the registry or by using a program that edits the registry.

Related Entries

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SynAttackProtect

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TcpMaxConnectResponseRetransmissions

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TCPMaxHalfOpen

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TCPMaxHalfOpenRetried

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