MaxFreeTcbs

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

Data type	Range	Default value
REG_DWORD	0x0–0xFFFFFFFF ( connections )	(Varies with the system and amount of physical memory on the computer. See description.)

Description

Determines the number of TCP control blocks (TCBs) the system creates to support active connections. Because each connection requires a control block, this value determines how many active connections TCP can support simultaneously. If all control blocks are used and more connection requests arrive, TCP can prematurely release connections in the TIME_WAIT state in order to free a control block for a new connection.

Normally, TCP does not release a connection or reuse its resources until the connection has remained closed for a period specified by the value of the TcpTimedWaitDelay entry. This interval is known as the TIME_WAIT or 2MSL (2 x maximum segment lifetime) state. However, if the system is supporting an unusually large number of connections and is running short of connection resources, TCP releases the connection before the value stored in the TcpTimedWaitDelay entry has expired.

The default value for this entry is determined both by the amount of physical memory on the computer when TCP/IP starts and by the version of Windows running on the computer, as shown in the following table.

Amount of physical memory	Windows 2000 Server	Windows 2000 Professional
Less than 19 MB	500	250
19–63 MB	1,000	500
64 MB or more	2,000	1,000

Note

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

TcpTimedWaitDelay