TCP/IPv4 and v6 Common Registry Settings
The following parameters apply to TCP/IPv4 as well as TCP/IPv6. Because the TCP implementations for TCP/IPv4 and TCP/IPv6 are separate, you may observe slightly different behavior when configuring these parameters for TCP/IPv4 and TCP/IPv6.
With the exception of the TCP/IP firewall registry entries, the parameters for TCP/IPv4 are located under the HKEY_LOCAL_MACHINE\Comm\Tcpip\Parms key. The parameters for TCP/IPv6 are located under the HKEY_LOCAL_MACHINE\Comm\Tcpip6\Parms key. The common settings must be configured under both keys for the TCP/IP implementation to work properly on your device.
Note The default registry values vary depending on which features are included in your platform. For more information, see Default Registry Settings.
The following table shows the registry values for the Parms registry key.
| Value : type | Description |
|---|---|
| EnablePMTUDiscovery : REG_DWORD | Default setting is 1 (True). This value can be either zero (0) (False) or 1 (True). Setting this value to 1 causes TCP to attempt to discover the Maximum Transmission Unit (MTU), or largest packet size, over the path to a remote host. For more information, see Path Maximum Transmission Unit (PMTU) Discovery. |
| EnableICMPRedirects : REG_DWORD | Default setting is 1 (True). This value can be either zero (0) (False) or 1 (True). Setting this value to 1 causes Windows to alter the route table in response to an ICMP redirect message that is sent to it by a network device, such as a router. |
| DisableUserTOSSetting : REG_DWORD | Reserved for system use. |
| GlobalMaxTcpWindowSize : REG_DWORD | This value is not set by default. This value determines the maximum TCP receive window size offered. The receive window specifies the number of bytes a sender can transmit without receiving an acknowledgment.
GlobalMaxTcpWindowSize is a system-wide value. There is a per-interface value, TcpWindowSize, which overrides the system-wide value. For more information about TCP receive window size and window scaling, see TCP Receive Window Size Calculation and Window Scaling. |
| KeepAliveInterval : REG_DWORD | Default setting is 1000 (one second). This value determines the interval in milliseconds between keep-alive retransmissions until a response is received. The valid range for this value is 1–0xFFFFFFFF (hexadecimal). For more information, see TCP Keep-Alive Messages. |
| KeepAliveTime : REG_DWORD | Default setting is 7,200,000 (two hours). This value controls how often TCP attempts to verify that an idle connection is still intact by sending a keep-alive packet. If the remote system is still reachable and functioning, it will acknowledge the keep-alive transmission. Keep-alive packets are not sent by default. This feature may be enabled on a connection by an application. The valid range for this value is 1–0xFFFFFFFF (hexadecimal). For more information, see TCP Keep-Alive Messages. |
| ResolverRetryCount : REG_DWORD | Default setting is 3. This value specifies the number of times that name resolution tries to resolve a name with DNS or WINS. This value can be any positive integer greater than or equal to 1. |
| TcpMaxConnectRetransmissions : REG_DWORD | Default setting is 2. The valid range for this value is 0–0xFF (hexadecimal). This value determines the number of times that TCP retransmits a connect request (SYN) before canceling the attempt. The retransmission time-out is doubled with each successive retransmission in a given connect attempt.
Note On IPv6 networks, Neighbor Discovery (ND) can take up to a minute to fail-over to another router. To enable TCP connections to survive long enough so that this fail-over has a chance to complete, the TcpMaxConnectRetransmissions setting does not have effect when set to below a certain amount. Retransmissions will continue for a time that is the greater of 1 minute or until the required number of retransmissions occur. |
| TcpMaxDataRetransmissions : REG_DWORD | Default setting is 5. The valid range for this value is 0–0xFF (hexadecimal). This value controls the number of times that TCP retransmits an individual data segment (not connection request segments) before canceling the connection.
Note On IPv6 networks, Neighbor Discovery (ND) can take up to a minute to fail-over to another router. To enable TCP connections to survive long enough so that this fail-over has a chance to complete, the TcpMaxDataRetransmissions setting does not have effect when set to below a certain amount. Retransmissions will continue for a time that is the greater of 1 minute or until the required number of retransmissions occur. For more information, see TCP Retransmission Behavior. |
| TcpWindowSize : REG_DWORD | Default setting is 0. The valid range for this value is 0–0x3FFFFFFF (hexadecimal). This value specifies the size of the TCP receive window. For more information about TCP receive window size and window scaling, see TCP Receive Window Size Calculation and Window Scaling. |
See Also
TCP/IP Registry Settings | IP Firewall Logging Registry Settings | IP Firewall Registry Settings | Default IP Firewall Rules
Last updated on Tuesday, May 18, 2004
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