# Windows NT Server 4.0 Notes
Module 11: Windows NT Network Services
Installing Network Services
Use Services tab in Network program in Control Panel to perform the functions Add, Remove, Properties and Update. Network services included with Windows NT Server include the following: DHCP = Dynamic Host Configuration Protocol WINS = Windows Internet Name Service DNS = Domain Name System Computer Browser Service
Dynamic Host Configuration Protocol (DHCP)
The DHCP Server service centralizes and manages the allocation of TCP/IP configuration information by automatically assigning IP addresses Subnet mask and Default Gateway to computers that have been configured to use DHCP. The Process in Brief Each time a DHCP client starts, it request TCP/IP configuration info from DHCP server. The DHCP server receives request, selects an IP address from pool of addresses defined in database and then offers it to the client for a specified period of time. Manual Configuring IP Addresses Potential problems: Entering an invalid address, or an address currently in use, can result in network problems. Entering an incorrect subnet mask can cause communication problems with other networks. There is administrative overhead if computers frequently move from one subnet to another. Using DHCP to Configure IP Addresses Advantages: Client receives valid IP address Configuration information is correct. DHCP Requirements A DHCP Server requires: DHCP Server service must be installed and properly configured on Windows NT Server (PDC, BDC or member server). It doesn't have to be on the PDC. DHCP Server must be configured with static IP address, subnet mask, and default gateway (optionally). If IP routers don't support RFC 1542, a DHCP Server is required on each subnet. DHCP scope must be created on DHCP Server.
Note:
A Windows NT Workstation can't be a DHCP Server
A DHCP Client is supported by following operating systems: ONLY Microsoft O/S's Windows NT Server or Workstation 3.5 or later Windows 95 Windows for Workgroups 3.11 Network Client 3.0 for MS-DOS LAN Manager 2.2c
The Four phase process to configure a DHCP client
Use ROSA as mnemonic
Phase | What happens | Description
1 - R | IP lease request | Client initializes a limited version of TCP/IP and broadcasts a request
2 - O | IP lease offers | All DHCP servers with valid IP addresses send an offer to client
3 - S | IP lease selection | Client selects IP address from first offer it receives and broadcasts request to lease the IP address
4 - A | IP lease acknowledgment | DHCP server that made offer responds to message and all other DHCP servers withdraw their offers. IP address is assigned to client and then an acknowledgment is sent to client. Client finishes initializing and binding TCP/IP protocol
Note:
If the computer has multiple network adapters, the DHCP process occurs separately for each adapter. A UNIQUE IP address will be assigned to each adapter in the computer.
Installing and Configuring the DHCP Server Service
First the Microsoft DHCP Server must be installed by means of Add in Services tab of the Network program. Now you can complete DHCP configuration by using DHCP Manager located in Administrative Tools group.
Creating and Configuring a DHCP Scope
Scope = range of IP addresses which the DHCP server can assign. Every DHCP server needs at least one scope. Each scope much contain UNIQUE IP addresses To create a DHCP scope, in DHCP Manager, on the Scope menu click Create. Following options can be configured in Create Scope dialog box.
Option | Use this option to
IP Address Pool Start Address | Specify first IP address that can be assigned to DHCP client. Required field.
IP Address Pool End Address | Specify last IP address that can be assigned to DHCP client. Required field.
Subnet Mask | Specify subnet mask to be assigned to all DHCP clients. Required field.
Exclusion Range Start Address | Specify first IP address to be excluded from IP addresses pool because of static IP addresses. This is important if there are static IP Addresses configured on non-DHCP clients Not required field.
Exclusion Range End Address | Specify last IP address to be excluded from IP addresses pool because of static IP addresses. This is important if there are static IP Addresses configured on non-DHCP clients Not required field.
Lease Duration Unlimited | DHCP leases assigned to clients will never expire.
Lease Duration Limited to | Specify number of days hours and minutes that a DHCP client lease is available before it must be renewed.
Name | Name to be assigned to DHCP scope. Is displayed after IP address in DHCP Manager. Required field.
Comment | Optional comments for scope.
Remember:
The Scope must be activated before the DHCP server can provide a DHCP client with a valid IP address. On Scope menu, click Activate.
Other DHCP Network Settings
Background: Setting up DHCP allows clients to participate in a TCP/IP network, but you probably want them to communicate with other computers beyond your subnet and beyond (i.e. the internet). You can give the client computers additional information automatically. What information? Domain name DNS addresses Default Gateway address by setting the DHCP global and scope options. Global options apply to all the scopes managed by the DHCP server. Scope options apply to a single scope. For example, if you had separate DNS and WINS servers in each IP subnet, you would use scope options. You reach Global and Scope options from the DHCP Options Menu These are just a few of the many network settings DHCP clients have access to, all of which can be configured through DHCP Manager.
Option | Use this option to configure a
003 Router | Default gateway
006 DNS Servers | IP addresses for name servers for client
044 WINS/NBNS Servers | IP addresses for NetBIOS name servers
Global Options Apply to all DHCP scopes defined on the selected DHCP server and all clients that lease an address from these scopes. Are used when all clients on all subnets require the same configuration information Global Options are always used unless scope or client options are configured DHCP Options menu, click Global Scope Options Apply to only the Specified scope and clients that lease an address from that scope Override global options; For example, use it to specify a unique default gateway address for each subnet DHCP Options menu, click Global Possible question: Client can't see past its subnet -->means Router Scope Option containing the IP address of the local router wasn't set. Client Options Apply to a specific client that has a reserved DHCP address lease Override scope or global options To configure client options, first create a client reservation; then in DHCP Manager, on Scope menu, click Active Leases. In Client Properties dialog box, click Client, click Properties and Options. Use this option for Win95 clients WfW 3.11 as long as its running TCP/IP MS-DOS 3.0 Clients can also get DHCP IP address assignment.
Background on NetBIOS Names
NetBIOS name is used for NetBIOS processes to communicate with each other. Is the computer name (or host name or UNC name) assigned during installation. Is stored as an entry in the registry, and can be changed through the Network Program in Control Panel. Is always specified in Windows NT commands, such as net use and net view. Can be determined by typing nbtstat -n at command prompt. Can be 15 characters in length. A 16 character can added to the name to designate the service or application that registered the name. ### Name Resolution: The process of converting a computer name to a media access control address (MAC address, physical address or burned-in address) is known as name resolution. Name resolution in a TCP/IP network is really a two-step process. Computer name-->IP address-->hardware address. Microsoft TCP/IP can use the following methods to resolve computer name to IP address. NetBIOS name cache: The local cache containing the locally registered computer names and the computer names that the local computer recently resolved to IP addresses. NetBIOS Name Server (NBNS) such as WINS: a server implemented under RFC 1001/1002 to provide name resolution of NetBIOS computer names. WINS is MS implementation of this. Local broadcast: A broadcast on the local network for the IP address of the destination NetBIOS name. LMHOSTS file: A local text file that maps IP addresses to NetBIOS computer names of Windows networking computers outside the local network. The file is stored in the \systemroot\System32\Drivers\Etc directory. HOSTS file: A local text file in the same format as the 4.3 Berkeley Software Distribution (BSD) UNIX/etc/hosts file. This file maps host names to IP addresses. This file is typically used to resolve host names for TCP/IP utilities. DNS: A server configured with the DNS daemon that maintains a database of IP address/computer name (host name) mappings. A DNS is common to UNIX environments. ### NetBIOS Over TCP/IP Name Resolution Modes B-node (broadcast): Uses broadcasts (UDP datagram) for name registration and resolution. In a large internetwork, broadcasts can increase the network load. Routers typically do not forward broadcasts, so only computer on the local network can respond. P-node (peer-to peer): Use NBNS, such as WINS to resolve NetBIOS name. P-node does not broadcast; instead, it queries the Name Server directly. Computer can span routers NBNS is down, computers will not be able to communicate even on the local network. M-node (mixed): First use b-node, then p-node. H-node (hybrid): First use p-node, then b-node. Microsoft enhanced b-node: Enhanced b-node utilizes the LMHOSTS file. Entries in the LMHOSTS file that marked with #PRE are cached when TCP/IP initializes. Before a b-node broadcast is sent, the cache is checked for the NetBIOS name/IP address mapping. If the mapping is not found in cache, a b-node broadcast is initiated. If the broadcast is not successful, the LMHOSTS file is parsed in an attempt to resolve the name. Summary: the order of inquiry is Look in name Cache from #PRE entry---> B-node broadcast---> Parse LMHOSTS FILE.
General Note:
You usually have to exclude the static IP address from the automatic workings of DHCP or WINS services, and it is a pain to keep entering them if you have a large network, so it is best to limit their use. You will have to supply a static IP address for DHCP server DNS server Default Gateway WINS server Actually, on a small network, one computer could do all of this. So then use DHCP to dole out all the other IP addresses to all other computers.
Windows Internet Name Service (WINS)
WINS Overview
WINS is used to register NetBIOS computer names (host names or UNC names) and resolve them to IP addresses. The WINS database is DYNAMIC It eliminates the need for an LMHOSTS file On a TCP/IP network a computer NEEDS an IP address to establish connections and can't do it using a NetBIOS computer name. This is the procedure: In a WINS environment, each time a WINS client starts, it registers its NetBIOS name/IP address mapping with a designated WINS server. When a WINS client initiates a NetBIOS command to communicate with another host, the name query request is sent directly to WINS server instead of being broadcast on the local network. If the WINS server finds a NetBIOS name/IP address mapping for the destination host in its database, it returns the destination host's IP address to the WINS client. Because WINS database obtains NetBIOS name/IP address mappings dynamically, it is always current. If the WINS server is unavailable, the client switches to b-node and sends the query as a broadcast message on the local subnet. WINS Server : WINS servers maintain a database that maps the NetBIOS computer names of WINS clients to their IP addresses. When WINS client requests an IP address, a WINS server retrieves the IP address from its database and routes it to the client. Requires: Must be configured on at least one computer running Windows NT Server within TCP/IP internetwork. Doesn't have to be a PDC or BDC Static IP address, subnet mask and default gateway WINS Clients: Registers its computer name and IP address with a WINS server during system startup; it then queries the WINS server for computer name resolution. To be a WINS client you need two things: NOTICE only Microsoft Clients can use WINS, because WINS is the Microsoft implementation of the resolution of host names -->IP addresses 1. To be one of these operating systems: These Windows-based systems can use WINS directly Windows NT Server/Workstation 3.5 or later Windows 95 Windows for Workgroups 3.11 running MS TCP/IP-32 These systems, which use broadcasts, can use WINS through a proxy Microsoft Network Client 3.0 for MS-DOS with real mode TCP/IP driver from NT Server CD LAN Manager 2.2c for MS-DOS (NT Server CD); LAN Manager 2.2c for OS/2 not supported 2. The IP address of a WINS server
Note:
Windows based network clients can use WINS directly. Non WINS computers that use broadcasts can access WINS through proxies. Proxies are WINS enabled computers that listen to name-query broadcast messages, forward the request to the WINS server, and then respond for names that are not on the local subnet.
Installing and Configuring WINS Same procedure as with DHCP but now select Windows Internet Name Service. WINS Manager appears in Administrative Tools group only on NT server on which it is installed. To give WINS a list of computers that have static IP addresses, you select Mappings --> Static Mappings-->Add Mappings ### Configuring a WINS Client Manually: You can manually add WINS server address to the WINS tab of TCP/IP properties dialog. Automatically: You can configure DHCP to provide WINS server address by add and configure 044 WINS/NTNS Server and 046 WINS/NBT Node Type.
Domain Name System
DNS is a distributed database providing a hierarchical naming system for identifying hosts on Internet. Below the root of the DNS file tree there are organizational names that classify the type of business. These are the top-level organizational names:
Name | Brief Description
com | commercial organizations
gov | government organizations
mil | Military organizations
net | Networking and Internet Service Providers
org | Non-commercial or non-profit organizations
int | International organizations
edu | Educational Institutions
The Domain Name Space
The DNS database is a tree structure called the domain name space. Each domain has a name and can contain subdomains, the root of the tree is at the top, and is represented by a period (.) With the exception of the root, each node in DNS database has a name (label) of up to 63 characters. Each subdomain must have a unique name within its parent domain. DNS domain names are formed by following the path from the bottom of the tree to the root. The node names are concatenated , and a period (.) separates each part. An optional period (.) that signifies the root can appear at the end of the name. What's a FQDN (Fully Qualified Domain Name)? DNS computer names consist of two parts: a host name and a domain name, which combine to form the FQDN. With the exception of the root, each node in the DNS database has a name (label) of up to 63 characters. DNS Server Service DNS Server service is a name resolution service that resolves an FQDN to the IP address that is then used by the internetwork.
DNS Operation
The main function of DNS is to resolve domain names to IP addresses. This is known as name resolution. DNS uses a client server model, in which DNS servers (name servers) contain information about the DNS database and make this information available to clients (resolvers) The name resolution process is as follows finding an IP address this FQDN: widgets.universal.com Resolver (client) passes a query to local name server. Local name server sends an iterative request to one of the DNS root servers, requesting resolution of the FQDN. DNS root server returns referral to name servers that are authoritative for the com DNS domain. Local name server sends an iterative request to one of the com name servers, which responds with a referral to the universal name servers. Local name server sends an iterative request to one of the universal name servers. Universal name servers are running the DNS Server service on a computer running Windows NT Server. They are configured to use WINS to resolve the leftmost portion (host name) of the FQDN. When the universal name server receives the request from the local name server, it passes the widgets piece of the DNS name to its local WINS server for resolution. WINS returns the IP address for widgets to the universal name server, which returns the IP address of the FQDN to the local DNS server, which then sends it back to the client resolver. Notice this done by integrating DNS and WINS: Integrating WINS and DNS Integration of WINS will allow DNS to query WINS for name resolution of the lower levels of the DNS tree in your zones. This way, DNS resolves the upper layers of the domain names and passes the final resolution to WINS for the local computer host name to IP address resolution. To configure DNS to use WINS to resolve the host name of a FQDN, use DNS Manager. Right-click the zone that will consult the WINS database for name resolution, and then click Properties. Click the WINS Lookup tab, and then select the Use WINS Resolution check box and type the WINS server IP address that will be used for resolution. DNS Benefits Access UNIX-based systems using friendly names. Connect to Internet systems using Internet naming conventions. Maintain an consistent hierarchical naming scheme across an organization.
Installing and Configuring the DNS Server Service
To Install: Double click on the Network Program of the Control Panel. On Services tab click Add and then select Microsoft DNS Server. To Configure: Use DNS Manager (in Administrative Tools group) to configure and manage DNS. Following table lists the objects that can be configured:
Object | Description
DNS Resource Record (RR) | Principle object in DNS. The component that contains actual information elements managed by DNS Three properties are common to all RR types: Owner, Class and TTL (Time to Live)
DNS Domain | Node in DNS tree that holds all resource records for that domain
DNS Zone | Subtree of the DNS database that is administered as a single entity. May contain single domain, or domain with subdomains
DNS Server | Used to administer at least one DNS zone
Server List | Contain DNS servers that can be administered with DNS Manager
Resource Record (RR) property set depends on the RR type. Next three are common.
Property | Function
Owner | Identifies DNS domain or host to which the RR applies.
Class | Identifies defined and standardized family of RR types. Almost all are "IN" or Internet class
TTL (Time to Live) | Shows how long information in RR will remain valid.
Note:
DNS Server requires a static IP address Servers are searched in the order that they appear in the DNS Manager
Configuring DNS Client:
DNS resolver functionality is included with Windows NT Server/Workstation Windows 95 ,and Windows for Workgroups 3.11 with Microsoft TCP/IP-32 installed. Manual Configuration Control Panel, Network, Protocols tab, TCP/IP Protocol, Properties. In Microsoft TCP/IP Properties dialog box, click DNS tab, and provide domain name for client, and search order for all DNS servers. In Conjunction with DHCP saves administrative overhead of individually configuring DHCP clients to also be DNS clients.
Integrating DNS and WINS
Differences:
DNS | WINS
Resolves Internet names to IP addresses | Resolves NetBIOS names to IP addresses
Static database and manually updated whenever a new host is added or when an existing host is moved to another subnet. | Dynamically database and dynamically updated
For clients running Microsoft operating systems and Non-Microsoft clients and hosts such as mainframes running TCP/IP and UNIX based computers | For Microsoft operating systems only
Computer Browser Service
The Computer Browser service maintains a centralized list of available network resources. This eliminates the need for all computers to maintain a list of shared resources on the network. This reduces network traffic.
The Browser Process
Browsers exist to provide networked computers with a list of the resources that are available on the networks. The steps that the requesting computer and the network browsers perform before and during a request are as follows: When each computer starts up and connects to the network, the computer announces its existence to the master browser in the workgroup or domain. If the computer has resources to share, it advertises them to the master browser. (Client to Master Browser: I'm here and this is what I have to share!) When the computer attempts to locate network resources for the first time, the computer contacts the master browser and retrieves a list of backup browsers. (Client to Master Browser: I want something-where do I get a list of what's available?) The computer contacts a backup browser and requests the network resource list. (Client to Backup Browser: Give me a who else in on the network) The backup browser responds with the list of domains and workgroups and the list of servers and client computers participating in the domain or workgroup that the computer is a part of. (Backup Browser to Client : Here's a list of who else is on the network) The computer contacts the server, domain controller, or workstation to request the list of resources shard by that entity. (Client to Resource holder: What stuff do you have to share?) That computer returns a list of resources to the requesting computer. Resources may now be selected by the client and a session established between the client and the share provider (Resource holder to Client : Here's the stuff I have to share. Connect to it if you can, depending on permissions I've set.)
Browser Types
Computers running Windows NT can perform any of the Browser service roles.
Browser type | Description
Domain Master Browser | There is only one Domain Master Browser in the domain, and it is the PDC collects and maintains the master list of available network servers and names of other domains and workgroups distributes this list to master browser of each subnet in domain
Preferred Master Browser | You can designate a computer on the network to be the preferred master browser. When this computer joins the network, it announces itself as the Master Browser. If the network already has a Master Browser, it will force an election that reevaluates the roles of computers as browsers in the network. The computer that is designated as the preferred master browser will win the election unless another computer is the primary domain controller or more than one computer is designated as the preferred master browser. To set a computer to be the Preferred Master Browser: Navigate in the registry to the following key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services Browser\Parameters Set the value of 'IsDomainMaster' to 'Yes'.
Master Browser | There is only one Master Browser for each workgroup or subnet of a domain. In a domain that spans multiple subnets, each subnet has it's own Master Browser that reports to the Domain Master Browser collects and maintains master list of available network servers in workgroup or subnet receives info about other workgroups, domains and subnets from domain master browser and incorporates this in the list distributes this list (browse list) to backup browser NOTE: only one Master Browser can exist in a workgroup or domain, except in the case of a TCP/IP internetwork. Because TCP/IP does not route broadcasts, the browsing process will not reveal shared resources through routers. Therefore, a master browser must exist in each TCP/IP subnetwork, with the PDC acting as a coordinating or Domain Master Browser.
Backup Browser | receives copy of browse list from master browser distributes list to browser clients upon request
Potential Browser | not a browser server but is capable of becoming backup or master browser if instructed by master browser or in absence of other browser servers
Non-Browser | configured that it will not maintain browse list peer-to-peer networked computers are commonly non-browsers despite their having server services.
Browser Elections
Elections happen when a master browser for the network or subnetwork can't be found. If client cannot locate master browser, or if backup browser attempts to update its network resource list, but cannot locate master browser, a new master browser must be elected. Network computers initiate election by broadcasting a special message called election packet this contains the requesting computer's criteria value. All browsers process the packet. When browser receives packet, it examines the packet and compares criteria of requesting computer with its own election criteria. If own criteria are higher, the browser issues its own election packet and enters "election-in-progress" state. This process continues until master browser is elected based on highest value.
Browser Criteria
Every domain or workgroup must have one and only one Master Browser (except TCP/IP as noted above). The hierarchical order is determined according to these criteria: This is the hierarchy: Browsing Role Operating System Operating System version The computer that is designated the Preferred Master Browser wins the election unless the network has a PDC. If the network doesn't have a Preferred Master Browser or a PDC, then these criteria are used to select the Master Browser: Designated role of the computer in network browsing. Preferred Master Master Browser Backup Browser Potential browser When computers run different operating systems but have the same browsing role, the operating system decides the election. This is the order of priority: Windows NT Server that is a PDC Windows NT Server that is a BDC Windows NT Server Windows NT Workstation Windows 95 Windows for Workgroups) When the Windows NT computers have the same role and the same operating system, the computer first in the list according to operating system version will win: 4.0 3.51 3.5 3.1
Configuring the Browser Role
To configure the browser role use Registry Editor There are three possibilities: become a browser never be a browser potentially be a browser This is the Registry path: \HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Browser \Parameters\MaintainServerList: These are the possible value in this key:
Value | Use this value to configure the computer to
Yes | Attempt to become browser server default for domain controllers
No | Never participate as browser server (computers which are frequently off line such as mobile computers)
Auto | Possibly be a browser server This is the default for non PDC or BDC Windows NT Server/Workstations
Trouble Shooting
Upon examining your TCP/IP configuration, you found that your subnet mask is 0.0.0.0, what's wrong? Duplicate IP addresses cause subnet mask to show 0.0.0.0 (i.e. When you make a mistake and manually assign duplicate IP address, the IP address will appear, but the subnet mask will show you 0.0.0.0 Upon examining your TCP/IP configuration, you found that your IP address is 0.0.0.0, what's wrong? The DHCP address is not available or no more addresses available. Your network contains both NT and UNIX computers and TCP/IP is the only protocol available on your network. You have a computer running NTW that is configured to use DNS and WINS. You can connect to NT computer but can not even Ping UNIX host on your network. What's wrong? The DNS server is either unavailable or does not contain a resource record for the UNIX host. Because DNS is not dynamic, you must manually enter resource records for your hosts. Connections to computers running NT are successful because these connections use WINS, not DNS.
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Last Updated: Wednesday, March 10, 1999 | Grant Wilson, Tisdale, SK. Canada