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Appendix B: NetBIOS over TCP/IP Configuration Parameters

Updated: July 6, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

All of the NetBIOS over TCP/IP (NetBT) parameters are registry values located under one of two different subkeys of HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services:

  • NetBT\Parameters

  • NetBT\Adapters\Interfaces\interface, in which interface refers to the subkey for a network interface to which NetBT is bound

Values under the latter key(s) are specific to each interface. If the system is configured using DHCP, a change in parameters takes effect if you issue the command ipconfig /renew from a command prompt. Otherwise, you must reboot the system for a change in any of these parameters to take effect.

Parameters Configurable Using the Registry Editor

The following parameters are installed with default values by Control Panel-Network Connections during the installation of the TCP/IP components. They may be modified using the Registry Editor (Regedit.exe). 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 NetBT driver.

BacklogIncrement

Key: Netbt\Parameters

Value Type: REG_DWORD—number

ValidRange: 3–0x14 (1–20 decimal)

Default: 3

Description: This parameter was added in response to Internet SYN-ATTACK issues. When a connection attempt is made to the NetBIOS TCP port (139), if the number of free connection blocks is below 2, a BackLogIncrement number of new connection blocks are created by the system. Each connection block consumes 78 bytes of memory. A limit on the total number of connection blocks allowed can be set using the MaxConnBackLog parameter. One connection block is required for each NetBT connection.

BcastNameQueryCount

Key: Netbt\Parameters

Value Type: REG_DWORD—number

Valid Range: 1–0xFFFF

Default: 3

Description: This value determines the number of times NetBT broadcasts a query for a specific name without receiving a response.

BcastQueryTimeout

Key: Netbt\Parameters

Value Type: REG_DWORD—time in milliseconds

Valid Range: 100–0xFFFFFFFF

Default: 0x2ee (750 decimal)

Description: This value determines the time interval between successive broadcast name queries for the same name.

BroadcastAddress

Key: Netbt\Parameters

Value Type: REG_DWORD—4-byte, little-endian encoded IP address

Valid Range: 0–0xFFFFFFFF

Default: The 1s-broadcast address for each network

Description: This parameter can be used to force NetBT to use a specific address for all broadcast name-related packets. By default, NetBT uses the 1s-broadcast address appropriate for each net (that is, for a network of 10.101.0.0 with a subnet mask of 255.255.0.0, the subnet broadcast address would be 10.101.255.255). This parameter would be set, for example, if the network uses the 0s-broadcast address (set using the UseZeroBroadcast TCP/IP parameter). The appropriate subnet broadcast address would then be 10.101.0.0 in the example above. This parameter would then be set to 0x0b650000. This parameter is global and is used on all subnets to which NetBT is bound.

CachePerAdapterEnabled

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 1 (true)

Description: This value determines whether NetBIOS remote name caching is done on a per-adapter basis. Nbtstat -c has been enhanced to show the per-adapter name cache.

CacheTimeout

Key: Netbt\Parameters

Value Type: REG_DWORD—time, in milliseconds

Valid Range: 0xEA60–0xFFFFFFFF

Default: 0x927c0 (600000 milliseconds = 10 minutes)

Description: This value determines the time interval that names are cached in the remote name table. The nbtstat –c command can be used to view the remaining time for each name in the cache.

ConnectOnRequestedInterfaceOnly

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 0 (false)

Description: This value can be used to allow NetBT connections on the requested adapter only. When the redirector on a multihomed computer calls another computername, it places calls on all NetBT transports (protocol/adapter combinations) to which it is bound. Each transport independently attempts to reach the target name. Setting this parameter limits each transport to connecting to other computers that are reachable via its own adapter, preventing crossover traffic. For more details, see the "NetBIOS Name Registration and Resolution for Multihomed Computers” section of this article.

It no longer works no wonder it doesn’t make sense.

EnableDns

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 1 (true)

Description: If this value is set to 1 (true), NetBT queries the DNS server for names that cannot be resolved by WINS, broadcast, or the Lmhosts file.

EnableProxyRegCheck

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 0 (false)

Description: If this parameter is set to 1 (true), the proxy name server sends a negative response to a broadcast name registration if the name is already registered with WINS or is in the proxy’s local name cache with a different IP address. This feature prevents a system from changing its IP address as long as WINS has a mapping for the name. For this reason, it is disabled by default.

InitialRefreshT.O.

Key: Netbt\Parameters

Value Type: REG_DWORD—time, in milliseconds

Valid Range: 960000–0xFFFFFFF

Default: 960000 (16 minutes)

Description: This parameter specifies the initial refresh time-out used by NetBT during name registration. NetBT tries to contact the WINS servers at one-eighth of this time interval when it is first registering names. When it receives a successful registration response, that response contains the new refresh interval to use.

LmhostsTimeout

Key: Netbt\Parameters

Value Type: REG_DWORD—time in milliseconds

Valid Range: 1000–0xFFFFFFFF

Default: 6000 (6 seconds)

Description: This parameter specifies the time-out value for Lmhosts and DNS name queries submitted by NetBT. The actual time-out could be as much as twice the value.

MaxConnBackLog

Key: Netbt\Parameters

Value Type: REG_DWORD—number

ValidRange: 2–0x9c40 (1-40,000 decimal)

Default: 1000

Description: This value determines the maximum number of connection blocks that NetBT allocates. See the BackLogIncrement parameter for more details.

MaxPreloadEntries

Key: Netbt\Parameters

Value Type: REG_DWORD—number

ValidRange: 0x3E8–0x7D0 (1000–2000 decimal)

Default: 1000 decimal

Description: This value determines the maximum number of entries that are preloaded from the Lmhosts file. Entries to preload into the cache are flagged in the Lmhosts file with the #PRE tag.

MaxDgramBuffering

Key: Netbt\Parameters

Value Type: REG_DWORD—number of bytes

Valid Range: 0x20000–0xFFFFFFFF

Default: 0x20000 (128K)

Description: This parameter specifies the maximum amount of memory that NetBT dynamically allocates for all outstanding datagram sends. Once this limit is reached, further sends fail due to insufficient resources.

MinimumRefreshSleepTime

Key: Netbt\Parameters

Value Type: REG_DWORD—number

Valid Range: 21600000-4294967295

Default: 21600000 ms (6 hours)

Description: This parameter is used to reset the TTL on the WakeupTimer if ½ of the TTL is less than 6 hours when the machine is put into sleep or hiberate mode.

MinimumFreeLowerConnections

Key: Netbt\Parameters

Value Type: REG_DWORD—number

Valid Range: 20-500

Default: 50

Description: This parameter is used allocate the number of free handles that the system has upon boot to accept incoming connections. These handles are allocated in addition to the number of active connections that are being serviced. Once the machine is in a steady state the number of free handles increases to ½ the value of the used handles. The number of free handles is never less than 50 unless specified in the registry.

NameServerPort

Key: Netbt\Parameters

Value Type: REG_DWORD—UDP port number

Valid Range: 0–0xFFFF

Default: 0x89

Description: This parameter determines the destination port number to which NetBT sends name service-related packets, such as name queries and name registrations, to WINS. The Microsoft WINS Server listens on port 0x89 (138 decimal). NetBIOS name servers from other vendors may listen on different ports.

NameSrvQueryCount

Key: Netbt\Parameters

Value Type: REG_DWORD—number

Valid Range: 0–0xFFFF

Default: 3

Description: This value determines the number of times that NetBT sends a query to a WINS server for a specified name without receiving a response.

NameSrvQueryTimeout

Key: Netbt\Parameters

Value Type: REG_DWORD—time in milliseconds

Valid Range: 100–0xFFFFFFFF

Default: 1500 (1.5 seconds)

Description: This value determines the time interval between successive name queries to WINS for a specified name.

NodeType

Key: Netbt\Parameters

Value Type: REG_DWORD—number

ValidRange: 1, 2, 4, 8 (b-node, p-node, m-node, h-node)

Default: 1 or 8 based on the WINS server configuration

Description: This parameter determines what methods NetBT uses to register and resolve names. A b-node system uses broadcasts. A p-node system uses only point-to-point name queries to a name server (WINS). An m-node system broadcasts first, and then queries the name server. An h-node system queries the name server first, and then broadcasts. Resolution through Lmhosts and DNS, if enabled, follows these methods. If this key is present, it overrides the DhcpNodeType key. If neither key is present, the system defaults to b-node if there are no WINS servers configured for the client. The system defaults to h-node if there is at least one WINS server configured.

NoNameReleaseOnDemand

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 0 (false)

Description: This parameter determines whether the computer releases its NetBIOS name when it receives a name-release request from the network. It was added to allow the administrator to protect the machine against malicious name-release attacks.

RandomAdapter

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 0 (false)

Description: This parameter applies to a multihomed host only. If it is set to 1 (true), NetBT randomly chooses the IP address to put in a name-query response from all of its bound interfaces. Usually, the response contains the address of the interface to which the query arrived. This feature would be used for load balancing by a server with two interfaces on the same network.

RefreshOpCode

Key: Netbt\Parameters

Value Type: REG_DWORD—number

Valid Range: 8, 9

Default: 8

Description: This parameter forces NetBT to use a specific opcode field in name-refresh packets. The specification for the NetBT protocol is somewhat ambiguous in this area. Although the default of 8 that is used by Microsoft implementations appears to be the intended value, some other implementations, such as those by Ungermann-Bass, use the value 9. Two implementations must use the same opcode field to interoperate.

ScopeId

Key: Netbt\Parameters

Value Type: REG_SZ—character string

ValidRange: Any valid DNS domain name consisting of two dot-separated parts or an asterisk (*).

Default: None

Description: This parameter specifies the NetBIOS name scope for the node. This value must not begin with a period. If this parameter contains a valid value, it overrides the DHCP parameter of the same name. A blank value (empty string) is ignored. Setting this parameter to the value “*” indicates a null scope and overrides the DHCP parameter.

SessionKeepAlive

Key: Netbt\Parameters

Value Type: REG_DWORD—time in milliseconds

Valid Range: 60,000–0xFFFFFFFF

Default: 3,600,000 (1 hour)

Description: This value determines the time interval between keep-alive transmissions on a session. Setting the value to 0xFFFFFFF disables keep-alives.

SingleResponse

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 0 (false)

Description: This parameter applies to a multihomed host only. If this parameter is set to 1 (true), NetBT supplies only the IP address from one of its bound interfaces in name-query responses. By default, the addresses of all bound interfaces are included.

Size/Small/Medium/Large

Key: Netbt\Parameters

Value Type: REG_DWORD

ValidRange: 1, 2, 3 (small, medium, large)

Default: 1 (small)

Description: This value determines the size of the name tables that are used to store local and remote names. In general, a setting of 1 (small) is adequate. If the system is acting as a proxy name server, the value is automatically set to 3 (large) to increase the size of the name cache hash table. Hash table buckets are sized as follows:

  • Small: 16

  • Medium: 128

  • Large: 256

SMBDeviceEnabled

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 1 (true)

Description: Windows Server 2003 supports a new network transport known as the SMB Device, which is enabled by default. This parameter can be used to disable the SMB device for troubleshooting purposes. See the "NetBT Internet/DNS Enhancements and the SMB Device" section of this article for more details.

TryAllNameServers

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 0 (false)

Description: This parameter controls whether the client continues to query additional name servers from the list of configured servers when a NetBIOS session setup request to one of the IP addresses fails. If this parameter is enabled, attempts are made to query all the WINS servers in the list and connect to all the IP addresses supplied before failing the request to the user.

TryAllIPAddrs

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 1 (true)

Description: When a WINS server returns a list of IP addresses in response to a name query, they are sorted into a preference order based on whether any of them are on the same subnet as an interface belonging to the client. This parameter controls whether the client pings the IP addresses in the list and attempts to connect to the first one that responds, or whether it tries to connect to the first IP address in the (sorted) list and fails if that connection attempt fails. By default, the client pings each address in the list and attempts to connect to the first one that answers the ping.

UseDnsOnlyForNameResolutions

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 0 (false)

Description: This parameter is used to disable all NetBIOS name queries. NetBIOS name registrations and refreshes are still used, and NetBIOS sessions are still allowed. To completely disable NetBIOS on an interface, see the NetbiosOptions parameter.

WinsDownTimeout

Key: Netbt\Parameters

Value Type: REG_DWORD—time in milliseconds

Valid Range: 1000–0xFFFFFFFF

Default: 15,000 (15 seconds)

Description: This parameter determines the amount of time that NetBT waits before trying to use WINS again after it fails to contact any WINS server. This feature primarily allows computers that are temporarily disconnected from the network, such as laptops, to proceed through boot processing without waiting to time out each WINS name registration or query individually.

Parameters Configurable from the Connections UI

The following parameters can be set using the Control Panel-Network Connections. There should be no need to configure them directly.

EnableLmhosts

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 1 (true)

Description: If this value is set to 1 (true), NetBT searches the Lmhosts file, if it exists, for names that cannot be resolved by WINS or broadcast. By default, there is no Lmhosts file database directory (specified by Tcpip\Parameters\DatabasePath), so no action is taken. This value is written by the Advanced TCP/IP Configuration dialog box.

EnableProxy

Key: Netbt\Parameters

Value Type: REG_DWORD—Boolean

ValidRange: 0, 1 (false, true)

Default: 0 (false)

Description: If this value is set to 1 (true), the system acts as a proxy name server for the networks to which NetBT is bound. A proxy name server answers broadcast queries for names that it has resolved through WINS. A proxy name server allows a network of b-node implementations to connect to servers on other subnets that are registered with WINS.

NameServerList

Key: Netbt\Parameters\Interfaces\interfaceGUID

Value Type: REG_MULTI_SZ—space separated, dotted decimal IP address (that is, 10.101.1.200)

ValidRange: any list of valid WINS server IP addresses.

Default: blank (no address)

Description: This parameter specifies the IP addresses of the list of WINS servers configured for the computer. If this parameter contains a valid value, it overrides the DHCP parameter of the same name. This parameter replaces the Windows NT 4.0 parameters NameServer and NameServerBackup, which are no longer used.

NetbiosOptions

Key: Netbt\Parameters\Interfaces\interfaceGUID

Value Type: REG_DWORD—number

Valid Range: 1, 2

Default: 1

Description: This parameter controls whether NetBIOS is enabled on a per-interface basis. On the Start menu, point to Settings, and click Network Connections. Right-click Local Area Connection, and click Properties. Select Internet Protocol (TCP\IP), and click Properties, then click Advanced. Click the WINS tab. The NetBIOS options are Enable NetBIOS over TCP\IP, Disable NetBIOS over TCP\IP, or Use NetBIOS setting from the DHCP server, the default. When enabled, the value is 1. When disabled, the value is set to 2. If this key does not exist, the DHCPNetbiosOptions key is read. If this key does exist, DHCPNetbiosOptions is ignored.

Non-Configurable Parameters

The following parameters are created and used internally by the NetBT components. They should never be modified using the Registry Edit or it can cause the component to become unstable. They are listed here for reference only.

DHCPNameServerList

Key: Netbt\Parameters\Interfaces\interfaceGUID

Value Type: REG_MULTI_SZ—space separated, dotted decimal IP address (that is, 10.101.1.200)

ValidRange: any list of valid WINS server IP addresses.

Default: blank (no address)

Description: This parameter specifies the IP addresses of the list of WINS servers, as provided by the DHCP service. This parameter replaces the Windows NT 4.0 parameters DHCPNameServer and DHCPNameServerBackup, which are no longer used. See also NameServerList, which overrides this parameter if it is present.

DHCPNetbiosOptions

Key: Netbt\Parameters\Interfaces\interfaceGUID

Value Type: REG_DWORD—number

Valid Range: 1, 2

Default: 1

Description: This parameter is written by the DHCP client service. See the NetbiosOptions parameter for a description.

DhcpNodeType

Key: Netbt\Parameters

Value Type: REG_DWORD—number

Valid Range: 1–8

Default: 1

Description: This parameter specifies the NetBT node type. It is written by the DHCP client service, if enabled. A valid NodeType value overrides this parameter. See the entry for NodeType for a complete description.

DhcpScopeId

Key: Netbt\Parameters

Value Type: REG_SZ—character string

ValidRange: a dot-separated name string such as microsoft.com

Default: none

Description: This parameter specifies the NetBIOS name scope for the node. It is written by the DHCP client service, if enabled. This value must not begin with a period. See the entry for ScopeId for more information.

NbProvider

Key: Netbt\Parameters

Value Type: REG_SZ—character string

ValidRange: _tcp

Default: _tcp

Description: This parameter is used internally by the RPC component. The default value should not be changed.

TransportBindName

Key: Netbt\Parameters

Value Type: REG_SZ—character string

Valid Range: N/A

Default: \Device\

Description: This parameter is used internally during product development. The default value should not be changed.

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