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Microsoft KB Archive/128233

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Article ID: 128233

Article Last Modified on 11/1/2006


  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Advanced Server 3.1

This article was previously published under Q128233


The following article on Windows NT protocols is a copy of an article published in Microsoft's "Premier Showing" newsletter.


Comparison of Windows NT Network Protocols


Microsoft provides three transport drivers (i.e., protocols) with Windows NT 3.5: TCP/IP, NWLink, and NBF. Windows NT 3.5 also ships with the DLC protocol, which does not provide transport layer services. In this article the terms TCP/IP, NWLink and NBF refer to the Windows NT transport drivers that implement the Internet TCP/IP, Novell SPX/IPX and IBM NetBEUI network protocol suites, respectively. This article compares these protocols as implemented in the Windows NT 3.5 transport drivers, to assist users in selecting the appropriate protocol(s) for their network.

Since each customer will be concerned with a different set of protocol characteristics, this article does not recommend which protocol customers should use. Instead, it discusses the merits of each, thereby enabling customers to make the best choice for their environment. Microsoft will continue to support these three protocols, today and in the long term.

Windows NT installs NWLink by default, primarily because IPX is the most common protocol in PC networks and it has relatively simple configuration requirements. However, administrators can modify setup.inf files to install other protocols by default. This default setting does not imply preference of NWLink over TCP/IP or NBF.

NOTE: In the Windows NT 3.51 release, TCP/IP is now installed by default.

Customers should generally use the minimum protocols necessary, because multiple protocols usually result in the following:

  • Higher memory requirement for clients.
  • More complex client configuration and network administration.
  • Higher support and software license costs.

Windows NT Transport Driver Architecture

The Network Basic Input/Output System (NetBIOS) standard, which was originally developed for IBM by Sytek in 1983 defines two entities:

  • A Session Layer interface that is a standard API for user applications to submit network I/O and control directives to underlying network protocol software. NetBIOS commands are submitted via Network Control Blocks (NCBs).
  • A session management/data transport protocol called NetBIOS Frames Protocol (NBFP). NBFP functions at the Session and Transport Layers to perform the network I/O to accommodate the NetBIOS interface command set.

An application program that uses the NetBIOS interface API for network communication can operate on any transport driver that exposes the NetBIOS interface. Transport drivers that do not implement NBFP (e.g., TCP/IP and IPX) must expose the NetBIOS interface and have a means of mapping each NetBIOS interface command to some sequence of their own native network frames and protocols.

Unlike the 16 bit Windows, MS DOS and OS/2 versions of Microsoft Network software, Windows NT transport drivers do not expose the NetBIOS interface; instead, they expose the more flexible Transport Driver Interface (TDI). Windows NT includes a NetBIOS Emulator to map NetBIOS commands to TDI commands and events. Internal Windows NT network components use TDI commands and events, rather than NetBIOS commands, to communicate with underlying transport drivers.

The TDI clients require support for NetBIOS address format and message mode data transfer. NBF supports this natively through NBFP. Transports that do not include NBFP implement a NetBIOS compatibility layer to resolve NetBIOS format addresses to the transport's native address format, and to implement message mode data transfer over the transport's native data transfer protocol.

Windows NT transport drivers provide the services defined in several layers of the OSI Reference Model: Some Session Layer services; all Transport and Network Layer services; and the services of the LLC sub layer of the Data Link Layer. This constitutes all services between the TDI and the Network Driver Interface Specification 3.0 (NDIS) interface. All Windows NT transport drivers except DLC export the TDI interface at their upper edge for communication with TDI client applications, such as the Windows NT redirector and server. They export the NDIS interface at the lower edge for communication with the underlying network interface card (NIC) driver.

Background on Windows NT Transport Drivers


IBM first introduced the NetBIOS Extended User Interface (NetBEUI) protocol specification in 1985. It is optimized for departmental LANs or LAN segments. The Windows NT NetBEUI Frame (NBF) transport driver implements the IBM NetBEUI 3.0 specification, and is completely compatible with the NetBEUI shipped with past Microsoft networking products. NBF implements NBFP, and therefore requires no NetBIOS compatibility layer.


Windows NT includes an implementation of the Transmission Control Protocol/Internet Protocol (TCP/IP). In general usage, the term TCP/IP refers to a suite of protocols that includes TCP, UDP, IP, ICMP, and ARP. Since TCP/IP is available for many diverse operating systems such as UNIX, MVS, VM, VMS, NetWare and OS/2, Windows NT can use TCP/IP to communicate with these different operating systems. TCP/IP also provides compatibility with the global Internet. TCP/IP is Microsoft's strategic protocol for scaleable Windows-based networking. The Windows NT TCP/IP transport driver includes TCP, UDP, IP, ICMP, ARP and NBT. Microsoft completely redesigned the TCP/IP transport driver in Windows NT 3.5, providing many enhancements over the Streams based TCP/IP transport driver in Windows NT 3.1. The NetBIOS compatibility layer for TCP/IP is NetBIOS over TCP/IP (NetBT in Windows NT 3.5; NBT in Windows NT 3.1).

NWLink (IPX)

Novell NetWare currently has the largest market share among PC based network operating systems. NetWare's native Network Layer protocol is IPX, a Novell proprietary descendant of the Xerox XNS protocol. Microsoft implements the lower level NetWare protocols in the NWLink transport driver, which includes IPX, SPX, RIPX and NBIPX. The NetBIOS compatibility layer for NWLink is NetBIOS over IPX, also known as NBIPX (NwLnkNb in Windows NT 3.5; NWNBLink in Windows NT 3.1).

Comparing Transport Driver Characteristics

This section compares the Windows NT transport drivers in each of the following areas:

  • Industry acceptance and experience
  • Open or proprietary specifications
  • Interoperability
  • Simplicity of configuration and administration
  • Network segmentation
  • Routing capabilities
  • Name registration and resolution requirements
  • Network traffic
  • Network status reporting
  • Memory requirements
  • Performance
  • Application programming support

As mentioned previously, the customer's computing environment will determine which protocol characteristics are desired, and which are most important. The applicability and importance of the foregoing characteristics will be dependent upon factors such as the following:

  • Size of the network
  • Single or multiple locations
  • Homogeneous or heterogeneous nodes
  • Internet connectivity requirements
  • Application programming requirements
  • Size and expertise of support staff

Industry Acceptance and Experience

The more popular protocols have a larger based of experienced support and design engineers. In late 1994 Sage Research, Inc. performed a study of router based LAN backbones with at least 250 nodes in Fortune 500 companies. Their study concluded that TCP/IP is used on 95% of all such networks, while SPX/IPX is used on 87%.

  • NetBEUI usage is limited primarily to Microsoft and IBM PC network environments.
  • TCP/IP is widely accepted, established and understood, especially in UNIX and non PC networks. It is the protocol of the global Internet.
  • SPX/IPX is the most popular protocol in PC network environments.

Open or Proprietary Specifications

Open protocol specifications enable programmers to obtain all the information necessary to develop their own protocol drivers without paying license fees.

  • NetBEUI is a proprietary specification owned by IBM. However, IBM makes this specification available to developers.
  • TCP/IP is an open specification. Anyone can easily obtain RFCs for implementing the TCP/IP protocols. Anyone can also submit RFCs to the Internet Engineering Task Force (IETF) for consideration.
  • SPX/IPX is a proprietary specification owned by Novell, which can make it difficult to obtain specifications for the upper layers like NCP. However, Novell has made the new SPX II specification available.


The availability of a protocol on a variety of operating systems and hardware platforms provides the advantage of interoperability. Windows NT provides native support for NetBEUI, TCP/IP and SPX/IPX through the NBF, TCP/IP and NWLink transport drivers.

  • NetBEUI is limited almost exclusively to Microsoft and IBM PC networks: Microsoft LAN Manager, Windows NT, Windows for Workgroups; LAN Manager for UNIX; and IBM PCLAN and LAN Server environments.
  • TCP/IP is available on a wide variety of operating systems such as Windows NT, UNIX, NetWare, VMS, VM, MVS, MS DOS, Macintosh, and OS/2. It is the protocol of the global Internet. NetWare/IP will enable NetWare customers to run TCP/IP-only networks, accessing NetWare services without requiring SPX/IPX. However, NetWare/IP is not native IP for NetWare; it emulates the IPX stack to NCP, which still requires an underlying IPX (or emulated IPX) layer. In comparison, Windows NT provides true protocol independent networking, running SMBs over its transport drivers without emulation requirements.
  • IPX is the native protocol of Novell NetWare. However, SPX/IPX is also available on other operating systems: Microsoft provides NWLink for Windows NT; TGV provides IPX for DEC VMS; Novell offers IPX on UnixWare.

Simplicity of Configuration and Administration

Administrators of any size network desire simplicity of client configuration and network administration. Large sites have many clients to configure, while small sites may not have sufficient support personnel. All three protocols are self tuning in their Windows NT 3.5 implementation. However, Microsoft exposes certain tuning parameters for manual configuration in special situations.

  • NBF requires little or no initial configuration or network administration.
  • TCP/IP is potentially difficult to configure due to the relative complexity of its multi part naming scheme, and the fact that a default gateway (router) must be identified for each station. To reduce the client configuration burden, Windows NT 3.5 supports the Dynamic Host Configuration Protocol (DHCP), an open standard that transparently provides dynamic negotiation of client configuration. DHCP clients require no manual IP configuration, and administrators do not have to manually assign IP addresses. However, DHCP does require proper planning and administration of DHCP servers.
  • NWLink requires little or no initial client configuration on small non routed networks. The node ID component of the IPX address is simply the six byte MAC address of the NIC. This simple node ID eliminates the need for manual client configuration. Configuring a server's external and internal networks is more complex, however.

Network Segmentation

Administrators of large networks desire the ability to differentiate between multiple interconnected networks. Hierarchical network addresses provide the ability to manage a hierarchy of subnetworks within networks, allowing smarter forwarding and security. Creating smaller segments with fewer stations produces more manageable networks with reduced traffic levels. This ability may not be critical for small networks.

  • NetBEUI uses a single part naming scheme, and therefore has no facility for differentiating between multiple interconnected networks.
  • TCP/IP uses a multi part naming scheme that allows very large multi location networks to be logically segmented into multiple levels of subnets. Network administrators can use the network ID component of the IP address in conjunction with a subnet mask to configure and manage subnetworks within subnetworks. IP uses subnetworks to logically segment large networks into separate, smaller interconnected subnetworks.
  • IPX uses a simple two part naming scheme that allows large multi location networks to be logically segmented into multiple subnets. However, the IPX network ID is not hierarchical; it does not divide into subcomponents.

Routing Capabilities

Multi location networks require routing capabilities, while single location networks have little use for such capabilities. Routable protocols do not generally allow broadcast packets to traverse routers, thereby reducing network congestion. Both IP and IPX are natively routable; they do not require encapsulation for routing. Both employ interior gateway protocols (IGPs) to exchange routing information among routers within an autonomous network (i.e., a group of nodes controlled by a single administrative authority). One of the most common IGPs is the Routing Information Protocol (RIP), which uses a vector distance algorithm to determine optimum routes. The RIP implementations used in IP and IPX are based upon the XNS RIP developed by Xerox Corporation's Palo Alto Research Center (PARC).

  • NetBEUI is not routable. NBF does support a simple form of routing known as Token ring Source Routing, offered only on Token Ring networks. However, source routing is not actually implemented at the OSI Network Layer.
  • TCP/IP packets are routeable by third-party routers that use RIP, IGPs such as Cisco Systems' Interior Gateway Routing Protocol (IGRP), or IETF's Open Shortest Path First (OSPF) protocol, even though Windows NT itself does not understand these protocols. However, if MPR is installed, Windows NT uses RIP. You may configure Windows NT as a static TCP/IP router by checking the Enable IP Routing check box in Control Panel. Dynamic routing must be implemented with third party routers.
  • Windows NT cannot act as an IPX router, but IPX provides full inter network routing support. NWLink uses Routing Information Protocol over IPX (RIPX) to implement route and router discovery services used by SPX and NBIPX. When NWLink loads, it sends out a RIPX request for a network number to be used for addressing at the IPX level. NetWare servers respond with a RIP packet containing the network number of the local network. If there is no RIPX response, NWLink uses 0 for the network number and indicates that the IPX packet is for the local subnet.

Name Registration and Resolution Requirements

Name resolution requirements impact the simplicity of client configuration and network administration. The methods of name registration and resolution impact the amount of broadcast or multicast activity present on the network, discussed later in the section on network traffic.

NetBIOS Name Registration

All transport drivers must register NetBIOS names to ensure that each name is unique.

NetBIOS Name Resolution

Application Layer names (NetBIOS and Sockets host names) must ultimately resolve to Data Link Layer (MAC) addresses. Transport drivers that do not process NetBIOS names natively have an intermediate name resolution step at the Network Layer, where the NetBIOS names resolve to the transport's native address format.

  • NBF uses NetBIOS names natively, then resolves them to MAC addresses.
  • In TCP/IP, NetBT resolves NetBIOS names to IP addresses, which then resolve to MAC addresses via ARP cache or broadcast.
  • In NWLink, NBIPX resolves NetBIOS names to IPX addresses. IPX addresses contain the MAC address as the host ID, so IPX requires no further resolution.

Sockets Host Name Resolution

For Windows Sockets applications, TCP/IP resolves host names to IP addresses, which then resolve to MAC addresses.

Network Traffic

The method of name registration and resolution often impacts the amount of broadcast or multicast (limited broadcast) activity present on the network. Broadcast and multicast activity uses network bandwidth on the local segment and on all bridged segments, and consumes processing cycles on every network station the same protocol. Protocols with a high level of broadcast or multicast activity are not generally well suited for large networks.

Name Registration Broadcasts

NetBIOS names must be registered to ensure that each name is unique. All transport drivers use broadcast, with one exception. In TCP/IP, WINS clients send directed name registration request to the WINS server. Non WINS clients may use WINS proxy agent for name resolution, but rely on broadcast for name registration. The MS DOS WINS clients send directed name resolution requests to the WINS server, but rely on broadcast for name registration.

Name Resolution Broadcasts

Name resolution may be accomplished by broadcast, cached mappings, lookup in a local mapping file or query a name service.

  • NBF does not cache NetBIOS names that have already been resolved to MAC addresses. NBF also does not use a mapping file or name service. Therefore, NBF will generate multicast activity each time a link to another station is re established.
  • TCP/IP in Windows NT 3.5 provides many options for name resolution, resulting in few broadcasts if configured properly. For NetBIOS name resolution, TCP/IP can use cache, LMHOSTS lookup, WINS query, broadcast, DNS query and HOSTS lookup. For host name resolution, TCP/IP can use all of these methods except cache. Regardless of the method used for resolving NetBIOS and host names, IP must resolve IP addresses to MAC addresses. This final resolution stage is accomplished by ARP cache or ARP broadcast.
  • NWLink uses broadcast to resolve names to addresses. However, NWLink reduces name resolution broadcast activity by caching NetBIOS name to IPX address mappings. NWLink does not use an address mapping file or name service. A future version may implement a name service similar to WINS or DNS.

Router Broadcasts

NetBEUI is not routable, and therefore has no impact on router broadcasts. Dynamic IP and IPX routers maintain routing tables by issuing a RIP broadcast on every port at regular intervals. IP broadcasts every 30 seconds; IPX, every 60 seconds. All NetWare file servers are inherently routers, and therefore issue RIP broadcasts. IP RIP allows for active or passive participants. Active participants issue RIP broadcasts; passive or silent participants only listen. IP routers are active whereas IP hosts are typically passive. Unfortunately, IP RIP does not communicate with IPX RIP, resulting in redundant RIP broadcasts on networks running both IP and IPX.

SAP Broadcasts

IPX servers use the Service Advertising Protocol (SAP) to automatically notify other IPX nodes of their presence and the services they provide. IPX servers, but not routers, issue SAP broadcasts every 60 seconds. Clients use SAP to determine what network resources are available. These SAP broadcasts may cause congestion on networks with numerous services, especially over WAN links. NWLink does not issue SAP broadcasts.

To address this problem on NetWare, Novell implemented SAP filters and the NetWare Link Service Protocol (NLSP) in its Multiprotocol Router (MPR) with NetWare 4.x. NLSP couples OSPF-based route information with Novell's SAP functions, substantially reducing the overhead traffic commonly generated by RIP and SAP.

DHCP Broadcasts

DHCP will greatly simply IP client configuration. However, DHCP will slightly increase network traffic. DHCP accomplishes client configuration negotiation through broadcast. Once the client accepts the IP address offered by the DHCP server, all activity is by directed packets. Since DHCP servers act autonomously, there is no replication traffic between DHCP servers.

WINS Replication

WINS can significantly reduce name query broadcasts. However, WINS will introduce network traffic for replication among multiple WINS servers. If configured properly, this replication traffic will be minimal and the net effect will be reduced network traffic.

Network Status Reporting

  • NBF does not provide any information about the state of the network.
  • TCP/IP routers use ICMP to notify the source that errors have been encountered, such as Destination Unreachable, Source Quench, etc.
  • IPX does not provide any information about the state of the network. IPX has no internet control management protocol, such as TCP/IP's ICMP. An IPX router has no way to indicate to a sending station that a destination is unreachable, that it should decrease its transmission rate, etc.

Memory Requirements

Network administrators generally desire a small memory footprint, especially on clients. Protocol memory requirements are typically a characteristic of the transport driver implementation rather than the protocol itself.

  • NBF has relatively small memory usage.
  • TCP/IP and IPX have similar memory usage requirements, but require more than NBF.


Protocol performance is typically dependent upon the efficiency and tuning of the transport driver implementation rather than the protocol itself.

  • NBF is tuned for small LAN communication, and therefore is very fast. Its performance across WANs is poor.
  • TCP/IP is not as fast as NBF on small LANs. The TCP/IP driver in Windows NT 3.1 was significantly slower than NBF on a local area network. However, the re designed TCP/IP in Windows NT 3.5 is only slightly slower than NBF.
  • NWLink is not as fast as NBF on small LANs. The NWLink driver in Windows NT 3.1 was significantly slower than NBF on a local area network. However, the re designed NWLink in Windows NT 3.5 is only slightly slower than NBF.
  • IPX/SPX protocols have some significant performance limitations in a routed (wide-area) network, which is why Novell has been modifying them with "packet burst" and "SPX II" changes.
  • IPX is only slightly faster than TCP/IP for file and print operations, and only slightly slower than TCP/IP for application services.

Application Programming Support

  • NBF enables NetBIOS, Named Pipes, Mailslot, NetDDE, RPC over NetBIOS, and RPC over Named Pipes programming using NBFP. NBF does not support Sockets or RPC over Sockets programming.
  • TCP/IP enables Sockets and RPC over Sockets application programming over TCP and UDP. TCP/IP also enables NetBIOS, Named Pipes, Mailslot, NetDDE, RPC over NetBIOS and RPC over Named Pipes programming over NBT.
  • IPX enables Sockets and RPC over Sockets application programming over SPX and IPX. IPX also enables NetBIOS, Named Pipes, Mailslot, NetDDE, RPC over NetBIOS and RPC over Named Pipes programming over NBIPX. IPX supports Socket IDs for use by Sockets applications and other applications that use IPX directly. This direct hosting capability allows IPX to realize performance advantages for small I/O by bypassing NBIPX and calling IPX directly.

       API                    TCP/IP          NWLink          NBF
       --------------------   -------------   -------------   ---
       NetBIOS                Yes (NBT)       Yes (NBIPX)     Yes
       Named Pipes            Yes (NBT)       Yes (NBIPX)     Yes
       Mailslot               Yes (NBT)       Yes (NBIPX)     Yes
       NetDDE                 Yes (NBT)       Yes (NBIPX)     Yes
       Sockets                Yes (TCP/UDP)   Yes (SPX/IPX)   No
       RPC over NetBIOS       Yes (NBT)       Yes (NBIPX)     Yes
       RPC over Named Pipes   Yes (NBT)       Yes (NBIPX)     Yes
       RPC over Sockets       Yes (TCP/UDP)   Yes (SPX/IPX)   No

Other Considerations

Users who wish to connect to the global Internet must obtain a network ID from InterNIC. The supply of unallocated IP addresses on the global Internet is rapidly declining. In an effort to address this problem the Internet Engineering Task Force (IETF) has formed IP Version 4 Address Lifetime Estimation (IPv4 ALE) working group to determine how much longer IPv4 can last. The IETF is also developing IP Version 6 (IPv6), also known as IP Next Generation (IPng), to replace the current IPv4. IPng increases the IPv4 addresses from four bytes (32 bits) to sixteen bytes (128 bits). However, there is much controversy over IPng.


Characteristic             TCP/IP           NWLink           NBF
Industry Acceptance        Most popular,    Primary protocol Limited to IBM
and Experience             especially in    in PC networks   & Microsoft PC
                           non PC networks                   networks
Open vs. Proprietary       Open             Proprietary      Proprietary,
Specification                                                but published</H3>
Interoperability           Available on     Available on     Limited to IBM
                           nearly every     many platforms   & Microsoft PC
                           platform                          networks
Simplicity of Client       Can be           Simple           Simple
Configuration              difficult
Simplicity of              Can be           Simple           Simple
Administration             difficult
Network Segmentation:

   Differentiates          Yes              No               No
   Between Networks
   Hierarchy of Subnets    Yes              Yes              No
   within Networks

Routing Capabilities       Native           Native           No
Name Resolution Requirements:

   Application Layer to    Resolves host    Resolves         Uses NetBIOS
   Network Layer           or NetBIOS name  NetBIOS name     names natively
                           to  IP address   to IPX address

   Network Layer to        Resolves IP      IPX address      Resolves
   Data Link Layer         address to MAC   contains MAC     NetBIOS name
                           address          address          to MAC address
Network Traffic:
   NetBIOS Name            WINS, Broadcast  Broadcast        Broadcast
   NetBIOS Name            Cache, WINS,     Cache,           Multicast
   Resolution              WINS Proxy,      Broadcast
                           HOSTS, DNS
   Router Broadcasts       Dynamic routers  Dynamic routers  N/A
                           issue RIP        & NetWare file
                           broadcasts       servers issue
                           every 30         RIP broadcasts
                           seconds          every 60 seconds
   SAP Broadcasts          N/A              IPX servers      N/A
                                            issue SAP
                                            broadcasts every
                                            60 seconds.
   DHCP Broadcasts         Client IP        N/A              N/A
                           negotiated via
   WINS Replication        Replication      N/A              N/A
                           traffic when
                           using multiple
                           WINS servers
Network Status Reporting   Yes              No               No
   Small LANs              Fast             Fast             Fastest
   File and Print          Fast             Fastest          Fast
   Application Services    Fastest          Fast             Fast


  • Windows NT 3.5 Concepts and Planning Guide, Chapter 2
  • Windows NT Server TCP/IP
  • Windows NT Server Solutions for NetWare Networks
  • Novell IPX Router Specification, Novell part number 107-000029-001
  • IBM LAN Technical Reference, IBM Publications, 39F9353, SC30-3383-03
  • Internetworking with TCP/IP, Volumes I and II, by Douglas E. Comer

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Keywords: kbnetwork KB128233