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Islam and Internet
ALAM Maritime
MISC Malaysia
What is Internet
American People
Rotterdam
50 States
Provinces of Canada
Palm Tree
TCP IP
Concept of Network
Specialized Servers
Workstaion Vs Server
Quraan in English
Dr Israr Ahmad
Poetry
Introducing NT
NT Protocols
Win NT Services
The Islands
Cool Links
Islamabad
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| WINDOWS NT SERVICES |
| The Material is provided by New Zealand University |
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| This section covers some of the basic Windows NT network services. These services run on a Windows NT server machine, and must be configured separately. All the following services rely on the TCP/IP protocol being installed on the server. ___________________________________________________________ Table of Contents: 1. DHCP 2. WINS 3. DNS 4. FTP 5. IIS 6. Peer Web Server ___________________________________________________________ DHCP (DYNAMIC HOST CONFIGURATION): Dynamic Host Configuration Protocol [DHCP] In TCP/IP networks, each computer must have a valid TCP/IP address. This address uses four digits separated by dots, e.g., 156.59.20.1 Each digit has a value between 1 and 254 [0 and 255 are special cases, 0 defining a network, 255 defining a group of computers]. This address can be assigned to the computer either statically or dynamically. Static TCP/IP addresses are generally used for servers which do not change their location on the network. The address of the computer is entered in via Control Panel->Networks->TCP/IP Protocol->Properties Dynamic TCP/IP numbers are numbers which are assigned to computers when they turn on, and in the past, have been assigned to these computers for a duration of time [how long they were powered on for]. Dynamic numbers have previously relied upon a BOOTP SERVER. This is a server which uses a static table, which has entries for all computers which require a TCP/IP address. This table, called the bootp table, has an entry which lists the network card MAC address and its TCP/IP number. When the computer is turned on, it issues a bootp request to the server. This bootp request contains the card address of the workstation issuing the request. The bootp server looks up the table and finds the correct TCP/IP address to issue to the workstation, then replies to the workstation with the TCP/IP address that the workstation is to use. The problems with the bootp approach is that - it relies upon static entries in a bootp table - if there is no entry for the workstation, the workstation cannot connect to the network - it requires administration in keeping the table up to date - IP addresses are allocated and cannot be used for another computer even if not currently in use - easy to run out of available IP addresses as the network grows An alternative to BOOTP has been to statically configure each workstation with a static IP address. This is done via the network configuration panel. This binds the IP address to the card. Whilst this might seem to be a good idea, the problems with this approach are, - a user can pick an IP address which conflicts with one already assigned to another computer - wrong values causes the computer to function incorrectly - moving the computer to a different part of the network requires allocation of a new IP address Microsoft addressed all of the above issues by using the Dynamic Host Configuration Protocol. A server acts as a DHCP server, and holds a number of free IP addresses available for allocation to workstation clients. A client computer, upon startup for the first time, issues a DHCP Discover to a DHCP server by sending a broadcast on the local subnet. The server responds to the client workstation with one of the unallocated IP addresses it has to offer, called a DHCP Offer. This is accepted by the client, which issues a DHCP request to the DHCP server. The DHCP server replies to the client with a DHCP acknowledgment, then marks this IP address as in use. The IP address given to the client is marked by the DHCP server as existing for a specific time duration. Periodically, the client will attempt to renew the leased IP address by contacting the DHCP server [occurs after 50% of the lease time has expired]. Whenever a client workstation is rebooted, it attempts to verify that its IP lease is valid for the subnet it is currently on. If the workstation is moved to a new subnet, this would be marked invalid by any DHCP server on that subnet, and the workstation will then request a new IP lease from any available DHCP server. The length of the lease time can be configured, and after a certain percentage of that lease time, the client workstation will contact the DHCP server to re-negotiate the IP lease. The advantages of the DHCP concept are: - IP addresses can be re-used, when the lease expires they are returned to the available pool - eliminates errors in configuration as subnet masks, DNS server and gateway IP addresses can be included in the lease - easy to move computers to another part of the network - require little or no intervention once configured [no tables to maintain] - setting up clients is simple [just enable it as a DHCP client], no need to know what the correct IP addresses are for things like subnet mask, gateway, wins servers or DNS servers - IP addresses conflicts are eliminated ___________________________________________________________ WINS (WINDOWS NAMING SERVICE): This service was designed to eliminate the need for broadcasts to resolve computer names to IP addresses. Previously, to find the address of a computer, a network broadcast packet was sent to all computers on the network. This broadcast contained the name of the computer which needed to be contacted. Each computer looked at the broadcast packet. The computer that recognized that the packet was destined for it responded with its IP address. The problem with this approach is that in large networks, the number of broadcasts becomes excessive and consumes the network. The name resolution has to take place, because Windows uses computer names to map drives and resources, e.g., \\ICE\WWW. The underlying protocol, TCP/IP, however, knows only IP addresses, like 156.59.21.12, so the broadcast is necessary to resolve the computer name to an IP address so that TCP/IP can establish the connection between the two computers. A WINS server maintains a database that maps computer names to IP addresses. Client workstations using WINS can query a WINS server and resolve computer names. A computer configured to use WINS as a client will register it's computer name and IP address with the WINS server. This happens at boot time. When a client workstation using WINS needs to resolve a computer name to an IP address, it will send a query to the WINS server, which will respond with the desired information. Using WINS servers in a Windows NT Domain helps to reduce broadcast traffic. It also is self maintaining, in that computers automatically add themselves to the database, and are automatically expired after a time interval when they shut down. ___________________________________________________________ DNS [Domain Name Service] DNS is a service which resolves computer names [like www.cit.ac.nz] to IP addresses [156.59.19.21] and IP addresses back to computer names [called a reverse lookup]. A DNS service has traditionally been implemented on a UNIX platform, but with the release of Windows NT 3.51, Microsoft released a beta version of its DNS server which will be an integral part of the Windows NT 4.0 release. We have already covered DHCP, which is a Windows NT service which dynamically allocates IP addresses to client computers, and WINS, which allows users to connect to resources using machine names [like \\cscp5nts], and acts in a similar way to DNS, resolving computer names to IP addresses. The important issue here is that the Windows NT services of DHCP and WINS are dynamic. DNS is a static service. It relies on a series of static files which contain mappings between computer names and IP addresses. There are two main lookup files, one for names to IP addresses, and the other for reverse name lookups. In NT 4.0, the DNS has a graphical interface, and can be remotely administered. In addition, the DNS is integrated with DHCP and WINS and the IP addresses which are dynamically allocated by DHCP are automatically reflected into the DNS. References: DNS and Bind: Paul Albitz and Cricket Lu [O'Reilly and Associates] FAQ: ftp://rtfm.mit.edu/pub/usenet/news.answers/internet/tcp-ip/domains-faq DNS Resources Directory: http://www.dns.net/dnsrd/ DNS Database Files: http://www.wcmh.com/uworld/archives/95/pcunix/005.html ___________________________________________________________ FTP [File Transfer Protocol]: Previous to version 4.0, Microsoft provided a separate FTP server for Windows NT. The server allows users to access files stored on the server using the FTP service. By combining NTFS security on the directory structure being used by the FTP service, a good level of security is achievable. The current trend is for Microsoft to combine this service with the IIS server being provided with Windows NT 4.0. You are recommended to run this server, rather than the separate FTP service. The FTP server portion of IIS is fully integrated with the WWW and other servers which form part of IIS. ___________________________________________________________ IIS [Internet Information Server]: This is a combination of servers [WWW, FTP, Gopher] which can be used to construct internet and intranet servers. Some advantages of IIS are: - fully integrated into Windows NT server - graphical installation - combines separate servers into one package [WWW, FTP, Gopher] - snmp mib provided for remote viewing of performance and statistics collection integrated into performance monitor, allowing real-time measuring of all Internet events - supports virtual servers [host multiple sites] - extensible API (application programming interface, which lets users write programs that use functionality within IIS) for custom server extensions - support for easy integration with existing databases - provides security using anonymous or NT domain accounts, or SSL (secure sockets layer, a means of secure transmission of information using web servers) References Microsoft IIS Home Page: http://www.microsoft.com/iis ___________________________________________________________ PEER WEB SERVER: This allows you to create a low-volume personal Web site on your local computer running Windows NT Workstation or Windows 95. You have the ability to share information over your network with others, an alternative to sharing files. Other users access your files by using Web browsers such as Microsoft Internet Explorer or Netscape Navigator. A personal Web Server is installed on your computer, which responds to HTTP requests from Web Browsers. Additional services such as FTP and Gopher can also be installed. The workstation must be running the TCP/IP protocol for the Peer Web Services to be installed and configured. You must also be logged on with Administrative privileges in order to install the product. A publishing directory [the root of the WWW] is created, and if documents are stored in or under this directory, those documents can then be accessed via a WWW browser by other users. The Peer Web Services installs an IUSR_computername account on the local Windows NT workstation computer. This account is used by the Web Server to access the files. As such, it is given rights to the publishing directory and local logon rights. Users who do not have a username account on the workstation computer logon to the computer as the IUSR_computername account. You can specify the directories to be used, enable logging and also enable authentification so that users have to enter usernames to access files. Actual file level permissions at the NTFS level determine whether users will be allowed access. |
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