Microsoft KB Archive/102973

= TCP/IP Transport Entries, Part 1 =

Article ID: 102973

Article Last Modified on 10/31/2006

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APPLIES TO


 * Microsoft Windows NT Advanced Server 3.1
 * Microsoft Windows NT Workstation 3.1
 * Microsoft Windows NT Advanced Server 3.1

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This article was previously published under Q102973



SUMMARY
The article contains REGISTRY entries for the TCP/IP Transport Entries, Part 1. These subgroups are included:


 * TCP/IP Parameters Subkey Entries
 * Adapter Card Parameters for TCP/IP

This is the first of two articles on these entries; for the other entries, see "TCP/IP Transport Entries, Part 2."

TCP/IP TRANSPORT ENTRIES
The various TCP/IP keys do not appear in the Registry unless TCP/IP is installed using the Network icon in Control Panel.

With Registry Editor, you can modify the following parameters for the TCP/IP transport. This section does not include all the TCP/IP parameters that can be set using the Networks application in Control Panel.

The startup parameters defined in this section are found in these subkeys of HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services:

  TCPIP\Parameters adapter_name#\Parameters\TCPIP, (where adapter_name# indicates a Services   subkey for a network adapter card)   Ftpsvc\Parameters NBT\Parameters Streams\Parameters

Parameters for network bindings for this service are described in the article "NetRules Subkey Entries." See also IsDomainMasterBrowser in the article "Browser Service Entries."

TCP/IP PARAMETERS SUBKEY ENTRIES
The entries for TCP/IP parameters appear under the following Registry path:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

ArpCacheLife REG_DWORD Number of Seconds
Default: 600 (10 minutes)

Determines the default lifetime for entries in the ARP cache table. Once an entry is placed in the ARP cache, it is allowed to remain there until its lifetime expires or until its table entry is reused because it is the oldest entry.

ArpCacheSize REG_DWORD Number
Default: 62

Determines the maximum number of entries that the ARP cache table can hold. The ARP cache is allowed to grow dynamically until this size is reached. After the table reaches this size, new entries can only be added by replacing the oldest entries that exist.

DatabasePath REG_EXPAND_SZ Pathname
Default: %SystemRoot%\system32\drivers\etc

Determines where TCP/IP and NBT look for the hosts, services, networks, protocols, NETRC, and LMHOSTS files.

IpEnableRouter REG_DWORD 0 or 1
Default: 0 (false)

Determines whether IP routing is enabled between local interfaces. IP routing is always enabled for packets generated by the local host. This parameter determines whether, for packets received on an interface and not destined for this host, IP will attempt to actively forward the packets to hosts that can be reached via its other interfaces.

IpReassemblyTimeout REG_DWORD Number of seconds
Default: 60 seconds

Determines how long IP accepts fragments when attempting to reassemble a previously fragmented packet. That is, if a packet is fragmented, all of the fragments must make it to the destination within this time limit; otherwise, the fragments will be discarded and the packet will be lost.

TcpDisableReceiveChecksum REG_DWORD 0 or 1
Default: 0 (false, that is, checksums will be checked on receives)

Specifies whether Checksums is disabled on receive.

TcpDisableSendChecksum REG_DWORD 0 or 1
Default: 0 (false, that is, checksums will be generated on sends)

Specifies whether Checksums is disabled on send.

TcpKeepCnt REG_DWORD Number in Minutes
Default: 120

Specifies how often TCP/IP will generate keep-alive traffic. When TCP/IP determines that no activity has occurred on the connection within the specified time, it generates keep-alive traffic to probe the connection. After trying TcpKeepTries number of times to deliver the keep-alive traffic without success, it marks the connection as down.

TcpKeepTries REG_DWORD Number
Default: 20

Specifies the maximum number of times that TCP/IP will attempt to deliver keep-alive traffic before marking a connection as down.

TcpLogLevel REG_DWORD Number
Default: 16 (log everything)

Specifies how verbose TCP/IP should be about logging events in the event log. The highest level of verbosity is 16, and 1 is the lowest level. The following shows general information about these levels.

  Level   Events to be included -  1     Only the most critical errors 4    Serious protocol violations 8    Nonserious protocol violations 12   Information about unusual events 16   Information about unusual events that some networks normally allow

TcpMaxConnectAttempts REG_DWORD Number
Default: 3

Specifies the maximum number of times TCP/IP attempts to establish a connection before reporting failure. The initial delay between connection attempts is 3 seconds. This delay is doubled after each attempt.

TcpMaxRetransmissionAttempts REG_DWORD Number
Default: 7

Specifies the maximum number of times that TCP/IP attempts to retransmit a piece of data on an established connection before ending the connection. The initial delay before retransmitting is based on the current estimate TCP/IP makes of the round-trip time on the connection. This delay is doubled after each retransmission. Acknowledgment of the data results in a recalculation of the estimate for the round-trip time.

TcpNumConnections REG_DWORD Number
Default: 64

Specifies the maximum number of TCP endpoints.

TcpRecvSegmentSize REG_DWORD Bytes
Default: 1460

Specifies the maximum receive segment size.

TcpSendDownMax REG_DWORD Number
Default: 16384

Specifies the maximum number of bytes queued by TCP/IP.

TcpSendSegmentSize REG_DWORD Bytes
Default: 1460

Specifies the maximum send segment size.

TcpWindowSize REG_DWORD Number
Default: 8192

Sets the size of the TCP send and receive windows, which is the amount of data that can be accepted in a single transaction. This parameter is important in transferring files between a client and a server and is critical for performance for one-way traffic, such as for FTP.

UdpDisableReceiveChecksum REG_DWORD 0 or 1
Default: 0 (false--that is, checksums will be checked on receives)

Specifies whether Checksums is disabled on receive.

UdpDisableSendChecksum REG_DWORD 0 or 1
Default: 0 (false--that is, checksums will be generated on sends)

Specifies whether Checksums is disabled on send.

UdpNumConnections REG_DWORD Number
Default: 64

Specifies the maximum number of UDP endpoints.

ADAPTER CARD PARAMETERS FOR TCP/IP
These parameters for TCP/IP are specific to individual network adapter cards. These appear under the following Registry path, where adapter name# refers to the Services subkey for the specific adapter card:

  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services

\adapter name#\Parameters\Tcpip

BroadcastType REG_DWORD 0 or 1
Default: 1 (all 1's)

Determines whether broadcast packets contain all 0's or all 1's as the broadcast address. The most common broadcast type is all 1's. The all-0's setting is provided for compatibility with BSD 4.2 systems.

ForwardBroadcasts REG_DWORD 0 or 1
Default: 0 (false)

Specifies whether broadcasts should be forwarded between adapters. If enabled, broadcasts seen by this interface are forwarded to other IP interfaces.

KeepAlive REG_DWORD 0 or 1
Default: 1 (true)

Determines whether TCP connections that request keep-alive packets result in keep-alive packets being sent. This feature is used to determine when inactive connections can be disconnected. When a connection becomes inactive, keep-alive packets are periodically exchanged. When 20 (the default value for TCPKeepTries) consecutive keep-alive packets go unanswered, the connection is broken. This disconnect is initiated by the endpoint that is sending keep-alive packets.

MTU REG_DWORD Number in octets
Default: 0 (That is, use the value supplied by the adapter.)

Specifies the maximum transmission unit size of an interface. Each interface used by TCP/IP may have a different MTU value specified. The MTU is usually determined through negotiation with the lower driver, using that lower driver's value. However, that value may be overridden.

Ideally, the MTU should be large enough to hold any datagram in one frame. The limiting factor is usually the technology making the transfer. Some technologies limit the maximum size to as little as 128; Ethernet limits transfers to 1500; and proNet-10 allows as many as 2044 octets per frame.

Datagrams larger than the MTU value are automatically divided into smaller pieces called fragments; size is a multiple of eight octets. Fragmentation usually occurs somewhere through which the traffic must pass whose MTU is smaller than the encapsulated datagram. If fragmentation occurs, the fragments travel separately to the destination computer, where they are automatically reassembled before the datagram is processed.

RouterMTU REG_DWORD Number in octets
Default: 0 (That is, use the value supplied by the lower interface.)

Specifies the maximum transmission unit size that should be used when the destination IP address is on a different subnet. Each interface used by TCP/IP may have a different RouterMTU value specified. In many implementations, the value of RouterMTU is set to 576 octets. This is the minimum size that must be supported by any IP node. Because modern routers can usually handle MTUs larger than 576 octets, the default value for this parameter is the same value as that used by MTU.

Trailers REG_DWORD 0 or 1
Default: 0 (false)

Specifies whether the trailer format is used. This feature provides compatibility with BSD 4.2 systems. When this feature is enabled, TCP/IP header information follows the data area of IP packets.

