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Microsoft DNS Server Registry Parameters, Part 1 of 3

This article was previously published under Q198408
IMPORTANT: This article contains information about editing the registry.Before you edit the registry, make sure you understand how to restore it ifa problem occurs. For information about how to do this, view the "Restoringthe Registry" Help topic in Regedit.exe or the "Restoring a Registry Key"Help topic in Regedt32.exe.
This article consists of 3 parts and describes settings for the MicrosoftDomain Name Service (DNS) SERVER. You can modify most settings using theDNSADMIN tool, although some settings can only be altered using RegistryEditor.

For additional information, please see the following articles in theMicrosoft Knowledge Base:

198409Microsoft DNS Server Registry Parameters, Part 2 of 3

198410Microsoft DNS Server Registry Parameters, Part 3 of 3
WARNING: Using Registry Editor incorrectly can cause serious problems thatmay require you to reinstall your operating system. Microsoft cannotguarantee that problems resulting from the incorrect use of Registry Editorcan be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing KeysAnd Values" Help topic in Registry Editor (Regedit.exe) or the "Add andDelete Information in the Registry" and "Edit Registry Data" Help topicsin Regedt32.exe. Note that you should back up the registry before you editit.

To change these parameters, use the following procedure:

  1. Start Registry Editor (Regedt32.exe).
  2. From the HKEY_LOCAL_MACHINE subtree, go to the following key:
  3. From the Edit menu, click Add Value and add a value to the key described in the appropriate entry below. Type in the value, and use the "Data Type" check box to set the value type.
  4. Click OK.
  5. Quit Registry Editor.
  6. Restart the DNS Server for the above changes to take affect.
All of the DNS parameters are registry values located under subkeys of:

Server Parameters

Several registry parameters determine behavior of the entire server. Eachof these is a registry value under

NOTE: These registry keys are read only at startup. Some may be reset and,in some cases, the server behavior dynamically changed, through the DNSAdministrator. But if manually reset the DNS server MUST be restarted topick up the new value.


   Value:      BootMethod   Added:    SP4 (April 98)   Type:     DWORD   Defaul    NoKey   Functio   Determine boot method.				

This key determines the source of the DNS boot information serverconfiguration, and list and configuration of authoritative zones. This keymakes the EnableBootMethod key (see below) obsolete.

NOTE: If the EnableRegistryBoot key is read, the DNS server will read itsvalue to determine the proper value of the BootMethod key; no administratorintervention is required. The EnableRegistryBoot key is kept around forbackward compatibility.

There are three possible sources of boot information and three possibleBootMethod values:
   #define BOOT_METHOD_UNINITIALIZED   (0)   #define BOOT_METHOD_FILE            (1)   #define BOOT_METHOD_REGISTRY        (2)				

  • When starting from a file, the DNS server attempts to locate a traditional BIND-style boot file. The file must be in the System32\Dns folder and be named <boot>. Note that, when starting from a boot file, the DNS server will still read server registry parameters that have no boot file analog. However, some server registry parameters may be configured in standard boot files:

    • Forwarders
    • Slave
    • NoRecursion
    For these, any existing registry entry will be deleted, whether or not they are specified in the boot file.

    NOTE: New versions of BIND have a new boot file style to attempt to provide a similar level of detailed control available in the Windows NT DNS server. This new style is NOT supported. Users should simply configure the DNS server through the DNS Manager and use registry or directory boot.
  • For a registry boot, all the server and zone configuration information is read from the registry. It is located in:
Starting with Windows NT 4.0 SP4, the DNS server is able to write back aboot file. Thus, administrator updates that alter boot file informationcause a new boot file to be written back. Furthermore, when starting fromthe boot file, the server will still check existing registry zoneinformation for values (for example, notify lists, secure secondaries) thatcan not be specified in a boot file.


   Value:      EnableRegistryBoot   Added     Windows NT 4.0   Type:     DWORD (Boolean)   Defaul    NoKey   Function: Determine boot method.				

Use of this key is only for pre-Service Pack 4 versions of Dns.exe; seeabove key "BootMethod" for explanation.

If the key does not exist or is 0, the server attempts to find a "boot"file in the DNS directory and use it to determine server configuration andauthoritative zones. If the boot file is NOT found, the server will startup with no authoritative zones as a caching-only server (a message islogged to this effect).

If the key is nonzero, DNS starts using only registry information, and theboot file, if any, is ignored.


   Value:      RpcProtocol   Added:    Windows NT 4.0   Type:     DWORD   Default:  0xffffffff (Use all protocols)   Function: Determine which protocols administrative RPC runs over				

If the key is nonzero, the key value is matched bit-wise against availableRPC protocols:
   TCP/IP      -- 0x1   NamedPipes  -- 0x2   LPC         -- 0x4				

For those protocols contained in the key, the DNS server sets up RPCendpoints to allow connections over those protocols from the admin tool.

Disabling RPC

If a computer is on the Internet, it is often desirable to disable RPC. Ifthis is being done for the entire computer, the DependOnService DNS serverkey (this is under DNS key, not under DNS\Parameters) should be edited toremove the last two entries, RpcSS and NtLmSsp. This eliminates thedependency of the DNS server on RPC and the standard Windows NT networksecurity information, allowing it to boot without those services.

Starting with Windows NT 4.0 SP4, the code is more responsive to a desireto turn RPC off. Setting the RpcProtocol key to zero will suffice.


   Value:      EventLogLevel   Added:    SP4 (April 98)   Type:     DWORD   Default:  NoKey (Log all events)   Function: Determines level of logging to event log.				

The DNS server can generate quite a few events of both a serious and aroutine nature. This key allows the administrator to limit the logging tothe level preferred.

The value of the key is the value of the LEAST serious event the DNS serverwill log, with the event types taken directly from the Win32 SDK:
   #define EVENTLOG_ERROR_TYPE             0x0001   #define EVENTLOG_WARNING_TYPE           0x0002   #define EVENTLOG_INFORMATION_TYPE       0x0004				

Examples: By default, a nonexistent EventLogLevel key has the value 4, andall events are logged. To log only warning and error events, set theregistry key to 2. To log only errors, set the registry key to 1. Todisable event logging completely, set the registry key to 0.


   Value:      LogLevel   Added:    SP4 (April 98)   Type:     DWORD (Bitfield)   Default:  NoKey (Zero -- No logging)   Function: Determines level of logging to file (Dns.log).				

The DNS server can generate a more detailed log than is practical toinclude in the Windows NT event log. This includes everything from simplyincluding events excluded from the event log, to a summary of every packetin and out of the server.

The registry key is a DWORD bit field indicating the various portions oflogging to enable:
   #define DNS_LOG_LEVEL_ALL_PACKETS      0x0000ffff   #define DNS_LOG_LEVEL_NON_QUERY        0x000000fe   #define DNS_LOG_LEVEL_QUERY            0x00000001   #define DNS_LOG_LEVEL_NOTIFY           0x00000010   #define DNS_LOG_LEVEL_UPDATE           0x00000020   #define DNS_LOG_LEVEL_QUESTIONS        0x00000100   #define DNS_LOG_LEVEL_ANSWERS          0x00000200   #define DNS_LOG_LEVEL_SEND             0x00001000   #define DNS_LOG_LEVEL_RECV             0x00002000   #define DNS_LOG_LEVEL_UDP              0x00004000   #define DNS_LOG_LEVEL_TCP              0x00008000   #define DNS_LOG_LEVEL_DS_WRITE         0x00010000   #define DNS_LOG_LEVEL_DS_UPDATE        0x00020000   #define DNS_LOG_LEVEL_FULL_PACKETS     0x01000000   #define DNS_LOG_LEVEL_WRITE_THROUGH    0x80000000				


   Value:      NoRecursion   Added:    Windows NT 4.0   Type:     DWORD (Boolean)   Default:  NoKey  (Do recursion)   Function: Determine whether or not server does recursive lookups.				

DNS server can answer queries for names outside of their authoritativezones in two ways:

  • Referral: Respond to query with the list (NS and A records) of "closest" servers to the queried name that it knows.
  • Recursion: Send query on to the "closest" DNS server to the queried name that it knows, and continue process (if necessary) until it gets a response back for the original query. Then send the response back to the client. A bit in the header of the DNS packet indicates the method preferred by the client.
If the NoRecusion key does not exist or is zero, the DNS server useswhichever method is requested in the packet.

If the NoRecursion key is nonzero, the DNS server always uses referralregardless of the client request. NoRecursion would generally be used whenclients are being limited to resolving names on a given server (forexample, names on an intranet), or when the server is incapable ofresolving external names and the clients are expected to fall over toanother DNS server for resolution of external (Internet) names.


   Value:      Forwarders   Added:    Windows NT 4.0   Type:     BINARY   Default:  NoKey (No forwarders)   Function: Determines forwarders server list.				

DNS servers may be configured to send all their recursive queries to aselected list of servers. Queries to these forwarders are done recursively(as a normal client query), rather than iteratively. The forwarder contactsthe remote server or servers until it gets the response and responds to theDNS server with the complete query response, suitable for sending back tothe client. During this process, the DNS server using forwardersessentially behaves as a DNS client to the forwarding server.

This behavior is often desirable when access to remote DNS servers (on theInternet) requires use of a slow or more expensive link. Using forwarderscan cut down on expensive traffic in two ways.

  • Cutting traffic across slow links.

    Example: Your DNS has a slow expensive dial-up connection to an ISP. When the DNS receives a query for a remote name, it can directly contact remote servers on the Internet until it can determine the authoritative server for the name, contact it, and get a response. This may involve several queries across the slow link. It is better to specify (if allowed) the ISP's DNS server on the Internet as a forwarder. The query is forwarded to this server and it does all the remote queries and responds only when it has the complete answer. This is a single round trip across the slow link.
  • Sharing remote results.

    Example: Your organization has several DNS servers on a LAN. Rather than have each server try and send queries through a firewall and out to the Internet, all the DNS servers are configured to forward queries to one DNS server (perhaps sitting on the firewall), which makes the necessary queries to the remote servers. In the process, this forwarding server will build up a rich cache from the responses it receives. And, when a local DNS server forwards a query to it, there is a reasonable chance that it already has the answer (or a head start on getting to the answer) from a previous query it answered for another DNS server. Thus, the total amount of remote traffic is reduced.
The forwarders list is a list of IP addresses of servers to forward to. Oneserver should be preferred (to preferentially build up its cache), but morethan one should generally be given. Retries are indicated by repeatingentries.

The Forwarders key is a list of IP addresses for the DNS server to forwardto. The list is not dotted IP strings, but a counted array of raw addressesin net byte order. It should be configured through the Server Properties,Forwarders dialog box in the Administrator tool. Editing the registry keyis discouraged. If the Forwarders key exists, the DNS server forwards toservers in the list. If the Forwarders key does not exist, the DNS serveruses the normal iterative query process to answer recursive queries forremote names.


   Value:      IsSlave   Added:    Windows NT 4.0   Type:     DWORD (Boolean)   Default:  NoKey (Not a slave)   Function: Determine if slave server.				

When a DNS server is using Slave (and Forwarders -- see Forwarders keydescription), it can stop and fail the query when it does not get aresponse from any of the forwarders servers /Vs Forwarders: configurationwhere the DNS server can attempt to resolve the query itself using normaliterative queries. The key is NOT read if Forwarders are not configured. Ifthe IsSlave key does not exist or is zero, the DNS falls back to normalrecursive query resolution when forwarders fail to respond.

If the IsSlave key is nonzero, the server fails (answers the original querywith SERVER_FAILURE) when the forwarders do not respond.

Do NOT change this key. Use the Forwarders dialog box in the DNSAdministrator tool to set forwarding properties. If this key is deletedwhile forwarders are configured, the server may fail to start or fail toresolve remote names properly.


   Value:      ForwardingTimeout   Added:    Windows NT 4.0   Type:     DWORD   Default:  NoKey   Function: Set forwarding timeout.				

When using forwarders, queries are sent to each forwarder in the list,which is given a timeout within which to respond before the next forwarderis tried. The ForwardingTimeout key is read ONLY when forwarders areconfigured. Its value determines the forwarding timeout in seconds.

Do NOT adjust this key. Use the Forwarders dialog box in the DNSAdministrator tool to set forwarding properties. If this key is deletedwhile forwarders are configured, the server may fail to start or fail toresolve remote names properly.


   Value:      ForwardDelegations   Added:    SP4 (April 1998)   Type:     DWORD (Boolean)   Default:  NoKey (Do NOT forward delegations.)   Function: Determine whether queries to delegated sub-zones are   forwarded.				

Queries to delegations are sent directly, not forwarded.


A server hosts and it is set up to forward across afirewall to Another server has a delegation to, acomputer inside the firewall. If the second server receives a query, the desired behavior is NOT tosend the query out to the forwarder. Rather it should send it directly

The ForwardDelegations value allows you to revert to previous forwardeverything behavior. This would only be desired when the delegation itselfwas at a remote site that was reachable through the forwarder.


   Value:      MaxCacheTtl   Added:    SP4 (April 1998)   Type:     DWORD   Default:  NoKey (Cache for up to one day)   Function: Set maximum caching TTL.				

Records from recursive queries are cached by the DNS server. The length oftime they remain in the cache is determined by the TimeToLive (TTL) fieldin the record. This field is a DWORD giving the caching time in seconds;therefore, the TTL can be quite long. Limiting the caching time can helplimit the memory used by the cache and make sure that stale data does notaccumulate in the cache.

Article ID: 198408 - Last Review: 10/31/2006 19:12:19 - Revision: 1.3

  • Microsoft Windows NT Server 4.0 Standard Edition
  • kbinfo KB198408