Parameters Configurable Using the Registry Editor
The following parameters receive default values during the installation of the TCP/IP components. A few of the parameters are visible in the registry by default, but most must be created in order to modify the default behavior of the TCP/IP protocol driver. Parameters configurable from the User Interface are listed separately.
Aliases
SubKey: Comm\Tcpip\Hosts\Host Name
Value Type: REG_MULTI_SZ
Default: <none>
Description: This value stores the aliases by which this host is known.
ArpUseEtherSNAP
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Boolean
Valid Range: 0, 1 (False, True)
Default: 0 (False)
Description: Setting this parameter to 1 forces TCP/IP to transmit Ethernet packets using 802.3 SNAP encoding. By default, the stack transmits packets in DIX Ethernet format. It will always receive both formats.
AutoCfg
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_DWORD
Valid Range: 0 or no value (disabled, enabled)
Default: No Value (enabled)
Description: This parameter specifies whether Automatic IP is enabled or disabled. Note that only the OEM of the device should set this option.
AutoInterval
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_DWORD – stored in seconds
Default: 300
Description: This parameter specifies the time interval used to check to see if a DHCP server is available to configure the device's adapter settings. (IP Address, SubnetMask, default gateway, DNS and WINS servers).
AutoIP
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_SZ – Dotted decimal IP address
Valid Range: <none>
Default: <none>
Description: This parameter specifies the last known AutoIP address used by this device. If there is no value present, a new IP address is generated.
AutoMask
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_DWORD
Valid Range: <none>
Default: 255.255.0.0
Description: This parameter specifies the default subnet mask for Automatic IP.
AutoSubnet
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_SZ
Valid Range: <none>
Default: 169.254.0.0
Description: This parameter specifies the default subnet for Automatic IP.
DefaultGateway
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_MULTI_SZ — List of dotted decimal IP addresses
Valid Range: Any set of valid IP addresses
Default: None
Description: This parameter specifies the list of gateways to be used to route those packets not destined for a subnet that the device is directly connected to, and for which a more specific route does not exist. This parameter, if it has a valid value, overrides the DhcpDefaultGateway parameter. There is only one active default gateway for the device at any point in time, so adding multiple addresses is only done for redundancy. For more information, see Dead Gateway Detection.
DefaultTOS
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Number
Valid Range: 1–0xFF (1–255 decimal)
Default: 0
Description: Specifies the default Type of Service (TOS) value set in the header of outgoing IP packets. See RFC 791 for a definition of the values.
DefaultTTL
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Number of seconds/hops
Valid Range: 1–0xFF (1–255 decimal)
Default: 128
Description: Specifies the default Time To Live (TTL) value set in the header of outgoing IP packets. The TTL determines the maximum amount of time an IP packet may live in the network without reaching its destination. It is effectively a limit on the number of routers an IP packet may pass through before being discarded.
DhcpInitDelayInterval
Key: Comm\Adapter Name\Params\Tcpip
Value Type: REG_DWORD, specified in milliseconds
Valid Range: Any positive integer
Default: 10,000
Description: This parameter specifies the initial delay between sending DHCP packets.
DhcpMaxRetry
Key: Comm\Adapter Name\Params\Tcpip
Value Type: REG_DWORD
Valid Range: Any positive integer
Default: 2
Description: This parameter defines the maximum number of attempts made to obtain a DHCP address.
DhcpNoMacCompare
Key: Comm\Adapter Name\Params\Tcpip
Value Type: REG_DWORD
Default: 0
Description: If this flag is set, the MAC address in DHCP packets returned from the server is compared against the local interface, and if it doesn't match, the packet is discarded.
DhcpOptions
Key: Comm\Adapter Name\Params\Tcpip
Value Type: REG_BINARY
Valid Range: 1–0xFF (1–255 decimal) — for more information, see RFC 2132.
Default: <none>
Description: Creating value names under this key in accordance with RFC 2132 allows you to specify the DHCP options that you would like the server to return. For example, if you create the value names 1, 3, and 5 under DhcpOptions, DHCP queries for the address mask, domain name, and router. By default, Windows CE 3.0 queries for the IP address, default gateway, subnet mask, DNS server, and WINS server. The values that the server returns, however, are not placed under DhcpOptions unless you create the value names.
DhcpRetryDialogue
Key: Comm\Adapter Name\Params\Tcpip
Value Type: REG_DWORD
Valid Range: <none>
Default: 2
Description: This parameter defines the number of retries before a dialog box is displayed with one of the following messages: "DHCP was unable to obtain an IP address. If the net card is removable, then you can remove/reinsert it to have DHCP make another attempt to obtain an IP address for it. Otherwise, you can statically assign an address," or, if the client's lease is still valid, "A DHCP Server could not be contacted. Using cached lease information," or, if the lease is no longer valid, "Your IP address lease has expired. DHCP was unable to renew your lease."
DhcpSendOptions
Key: Comm\Adapter Name\Params\Tcpip
Value Type: REG_BINARY
Valid Range: <none>
Default: <none>
Description: This registry key stores the options that you would like to send to the DHCP server. These options need to be valid and recognizable by the server. These options are copied into the DHCP packet. Because Windows CE does not parse the data, you are responsible for being sure that the options you specify are valid DHCP options.
DNS
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_MULTI_SZ — Dotted decimal IP address
Valid Range: Any valid IP address
Default: None
Description: This value stores the IP address of the DNS name server. Note that there can be two DNS servers listed.
DNSDomain
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: domain name — for example, redmond.mcrosoft.com
Default: <none>
Description: This parameter stores the domain name that is used by the network to which the device is connected.
DNSTimeOut
Key: Comm\Adapter Name\Parms\Tcpip
Valid Range: stored in milliseconds
Default: 3000
Description: This parameter specifies the length of time, in milliseconds, that name resolution waits for a response from the DNS server.
DontAddDefaultGateway
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_DWORD — Boolean
Valid Range: 0, 1 (False, True)
Default: 0
Description: When you install PPTP, a default route gets installed for each LAN adapter. You can disable the default route on an adapter by adding this value and by then setting it to 1. After doing so, you may need to configure static routes for hosts that are reached using a router other than the default gateway.
EnableDeadGWDetect
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Boolean
Valid Range: 0, 1 (False, True)
Default: 1 (True)
Description: Setting this parameter to 1 causes TCP to perform dead gateway detection. With this feature enabled, TCP may ask IP to change to a backup gateway if a number of connections are experiencing difficulty. Backup gateways may be defined by using the Route utility or the IP Helper API.
EnableDhcp
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_DWORD — Boolean
Valid Range: 0, 1 (False, True)
Default: 0 (False)
Description: If this parameter is set to 1 (True), the DHCP client service will attempt to use DHCP to configure the first IP interface on this adapter.
EnablePMTUDiscovery
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Boolean
Valid Range: 0, 1 (False, True)
Default: 1 (True)
Description: Setting this parameter to 1 (True) causes TCP to attempt to discover the Maximum Transmission Unit (MTU, or largest packet size) over the path to a remote host. By discovering the Path MTU and limiting TCP segments to this size, TCP can eliminate fragmentation at routers along the path that connect networks with different MTUs. Fragmentation adversely affects TCP throughput and increases network congestion. Setting this parameter to 0 causes an MTU of 576 bytes to be used for all connections that are not to hosts on the local subnet.
ExpireTime
SubKey: Comm\Tcpip\Hosts\Host Name
Value Type: REG_BINARY
Value Length: 8
Default: <none>
Description: If the current time, obtained by calling GetCurrentFT, exceeds the value in ExpireTime, the entire Host Name subkey is deleted the next time that gethostbyname is called.
GlobalMaxTcpWindowSize
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Number of bytes
Valid Range: 0–0xFFFF (0–65,535 decimal)
Default: This parameter does not exist by default.
Description: The TcpWindowSize parameter can be used to set the receive window on a per-interface basis. This parameter can be used to set a global limit for the TCP window size on a system-wide basis.
Host Name
Key: Comm\Tcpip\Hosts
Description: This value stands for the name of a host, and is a subkey that contains three values: ExpireTime, ipaddr, and aliases. For more information about these values, see the separate entries for these values. The registry is queried first when an application calls gethostbyname, before a DNS or WINS request is sent. If the host name is found in the registry, the registry values are returned.
IGMPLevel
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Number
Valid Range: 0,1,2
Default: 2
Description: This parameter determines to what extent the system supports IP multicasting and how fully it participates in the Internet Group Management Protocol (IGMP). At level 0, the system provides no multicast support. At level 1, the system can send IP multicast packets, but cannot receive them. At level 2, the system can send IP multicast packets and fully participate in IGMP to receive multicast packets.
ipaddr
Subkey: Comm\Tcpip\Hosts\Host Name
Value Type: REG_BINARY
Value Length: 4 bytes per address
Default: <none>
Description: This value stores the list of IP addresses associated with this host name.
IPAddress
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_MULTI_SZ — List of dotted-decimal IP addresses
Valid Range: Any set of valid IP addresses
Default: <None>
Description: This parameter specifies the IP addresses of the IP interfaces to be bound to the adapter. A system with more than one IP interface for an adapter is logically multihomed. There must be a valid subnet mask value in the SubnetMask parameter for each IP address specified in this parameter. To add parameters use any registry editor to select this key and type the list of IP addresses, pressing the ENTER key after each one. Then select the SubnetMask parameter, and type a corresponding list of subnet masks.
IPEnableRouter
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Boolean
Valid Range: 0, 1 (False, True)
Default: 0 (False)
Description: Setting this parameter to 1 (True) causes the system to route IP packets between the networks to which it is connected.
KeepAliveInterval
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Time in milliseconds
Valid Range: 1–0xFFFFFFFF (1–4,294,967,295 decimal)
Default: 1000 (one second)
Description: This parameter determines the interval between keep-alive retransmissions until a response is received. Once a response is received, the delay until the next keep-alive transmission is again controlled by the value of KeepAliveTime. The connection will be aborted after the number of retransmissions specified by TcpMaxDataRetransmissions have gone unanswered.
KeepAliveTime
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Time in milliseconds
Valid Range: 1–0xFFFFFFFF (1–4,294,967,295 decimal)
Default: 7,200,000 (two hours)
Description: The parameter 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.
Name
Key: \Ident\
Value Type: REG_DWORD
Valid Range: none
Default: <none>
Description: This parameter stores the name of the device if an OEM decides to specify a name. Redirector or MSMQ need to be started before you can register the name with WINS. Also, if you update this registry key after Redirector and /or MSMQ has started, you need to reset the interface by either removing and then reinserting the PCMCIA card, using the ipconfig /release command followed by the ipconfig /renew command, or using the IP Helper API.
NoIdleIfConnected
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Boolean
Description: This setting controls going into Idle mode during TCP/IP communications, and is independent of the NoIdleIfAdapter setting. If set to 0 (FALSE), the device may enter Idle mode even in the middle of communicating with another device, or over loopback. If set to TRUE, the device will not idle and will maintain an active TCP/IP connection, even if there is no active network adapter.
NoIdleIfAdapter
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Boolean
Description: This setting controls going into Idle mode during TCP/IP communications, and is independent of the NoIdleIfConnected setting. If set to TRUE, the device will not idle as long as there is a network adapter in use in the device.
ResolverCheckCacheFirst
Key: Comm\AFD\
Value Type: REG_DWORD — Boolean
Valid Range: 0, 1 (false, true)
Default: 1 (true)
Description: This parameter controls whether or not the cache is checked first when resolving names, before the WINS and DNS servers are queried.
ResolverRetryCount
Key: Comm\Adapter Name\Parms\Tcpip
Valid Range: Any number greater than or equal to 1
Default: 3
Description: This parameter specifies the number of times that name resolution tries to resolve a name with DNS or WINS.
SackOpts
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — Boolean
Valid Range: 0, 1 (false, true)
Default: 1 (true)
Description: This parameter controls whether or not Selective Acknowledgment (SACK, specified in RFC 2018) support is enabled. For more information about SACK, see TCP Selective Acknowledgment.
SubnetMask
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_MULTI_SZ — List of dotted decimal IP addresses
Valid Range: Any set of valid IP addresses
Default: <none>
Description: This parameter specifies the subnet masks to be used with the IP interfaces bound to the adapter. There must be a valid subnet mask value in this parameter for each IP address specified in the IPAddress parameter.
TCP1323Opts
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD — number (flags)
Valid Range: 0, 1, 2, 3
| Value | Description |
|---|---|
| 0 | Disables RFC 1323 options |
| 1 | Enables window scaling only |
| 2 | Enables timestamps only |
| 3 | Enables both options |
Default: No value; the default behavior is: do not initiate options but provide them if requested.
Description: This parameter controls RFC 1323 time stamps and window-scaling options. Time stamps and window scaling are enabled by default, but can be manipulated with flag bits. Bit 0 controls window scaling, and bit 1 controls timestamps.
TcpDelAckTicks
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_DWORD — Number, expressed in milliseconds
Valid Range: 0–6
Default: 200
Description: Specifies the number of milliseconds to use for the delayed-ACK timer on a per-interface basis. By default, the delayed-ACK timer is 200 milliseconds. Setting this value to 0 disables delayed acknowledgments, which will cause the device to immediately ACK every packet it receives. Microsoft does not recommend changing this value from the default without careful study of the environment.
TcpInitialRTT
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_DWORD — Number
Valid Range: 0–0xFFFF (0–65,535 decimal)
Default: 3
Description: This parameter controls the initial time-out used for a TCP connection request on a per-interface basis. Use caution when tuning with this parameter, because exponential backoff is used. Setting this value larger than 3 will result in much longer time-outs to nonexistent addresses.
TcpMaxConnectRetransmissions
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD-number
Valid Range: 0–0xFF (0-255 decimal)
Default: 2
Description: This parameter determines the number of times that TCP retransmits a connect request (SYN) before aborting the attempt. The retransmission time-out is doubled with each successive retransmission in a given connect attempt.
TcpMaxConnectResponseRetransmissions
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD-number
Valid Range: 0–0xFF (0-255 decimal)
Default: 2
Description: This registry setting controls how many times a SYN-ACK is retransmitted before aborting the attempt when responding to a SYN from a remote device.
TcpMaxDataRetransmissions
Key: Comm\Tcpip\Parms
Value Type: REG_DWORD-number
Valid Range: 0–0xFF (0-255 decimal)
Default: 5
Description: This parameter controls the number of times that TCP retransmits an individual data segment (not connection request segments) before aborting the connection. The retransmission time-out is doubled with each successive retransmission on a connection. It is reset when responses resume. The Retransmission Timeout (RTO) value is dynamically adjusted, using the historical measured round-trip time (Smoothed Round Trip Time, or SRTT) on each connection.
TcpWindowSize
Key: Comm\Tcpip\Parms, Comm\Adapter Name\Parms\Tcpip
Value Type: REG_DWORD — Number of bytes
Valid Range: 0–0x3FFFFFFF (0–1073741823 decimal). Values greater than 64K can be achieved only when connecting to other systems that support RFC 1323 Window Scaling, which is discussed in the TCP section of this document.
Default: The smaller of the following values:
0xFFFF (65,535 decimal)
GlobalMaxTcpWindowSize (another registry parameter)
The larger of four times the maximum TCP data size on the network
16,384 rounded up to an even multiple of the network TCP data size.
The default can start at 17,520 for Ethernet, but may shrink slightly when the connection is established to another device that supports extended TCP head options, such as SACK and TIMESTAMPS. These options increase the TCP header beyond the usual 20 bytes, leaving slightly less room for data.
Description: This parameter determines the maximum TCP receive window size offered. The receive window specifies the number of bytes a sender can transmit without receiving an acknowledgment. In general, larger receive windows will improve performance over high-delay, high-bandwidth networks. For greatest efficiency, the receive window should be an even multiple of the TCP Maximum Segment Size (MSS). This parameter is both a per-interface parameter and a global parameter, depending upon where the registry key is located. If there is a value for a specific interface, then that value overrides the system-wide value. See also GobalMaxTcpWindowSize.
WINS
Key: Comm\Adapter Name\Parms\Tcpip
Value Type: REG_MULTI_SZ — Dotted decimal IP address
Valid Range: Any valid IP address
Default: <none>
Description: This value stores the IP address of the WINS name server. Note that there can be two WINS servers listed.
WinsBroadcastTimeOut
Key: Comm\Adapter Name\Parms\Tcpip
Valid Range: stored in milliseconds
Default: 500
Description: This parameter stores the length of time, in milliseconds, that name resolution waits for a response to the IP subnet broadcast.
WinsTimeOut
Key: Comm\Adapter Name\Parms\Tcpip
Valid Range: stored in milliseconds
Default: 2000
Description: This parameter stores the length of time, in milliseconds, that name resolution waits for a response from the WINS server.
Last updated on Friday, April 02, 2004
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