Lecture 3:More on Servers &ServicesNetwork Design & Administration
“Domain” Controller• A Domain Controller provides centralised control of users and access control to resources (e.g. shares, printers, etc)• Microsoft Server systems can be promoted to be Network Design & Administration domain controllers – in Active Directory Domain Services (AD DS) they hold a copy of the AD DS database.• They are so important, there should be redundant ones! 2• We will cover AD DS in more detail in a future lecture.
Server Roles: File & PrintServers• Some servers may simply provide file storage.• Some may be used to ease latency in printing (covered in a later session)• Question: Network Design & Administration • Are there any other operating systems which could be found within a corporate network?• SAMBA allows Linux server to provide these services to Windows or Linux clients.• “Samba is an open source / free software suite that provides file and print services to SMB/CIFS clients” 3
Server Role: Windows InternetName Service (WINS)• Provides resolution of names to IP address.• Works on NetBIOS names (flat namespace).• Needed if Microsoft machines prior to Windows 2000 on network. Since then, DNS preferred and best not to install WINS.• However, some apps, e.g. SQL Server 2000, Exchange Server 2003 Network Design & Administration still need WINS.• Recommended to have redundant WINS servers – a primary and multiple secondary servers.• No difference between servers – clients just choose to query to query in specific order.• Clients use secondarys only when primary is: • Unavailable on the network when the service request is made, or • Unable to resolve a name for the client (in the case of a name 4 query)
Domain Name System (DNS)• Originally networks were very small – even ARPANET – so used a (manually modified) list of machines and addresses on each host and then a central list file at a particular server. Network Design & Administration• The manual list still exists as etc/hosts on both Linux and Windows (mine just contains: 127.0.0.1 localhost).• Unrealistic for large dynamic nets (e.g. the internet).• Needs servers to work out the IP addresses given a human memorable symbolic name for a machine.• If name servers are not available, small networks can survive by broadcast queries. 5
Domain Name Service (DNS)• Software to resolve names against addresses has been around since 1983.• Tree structure of domain names allows client to find out address by sending request up the tree. Network Design & Administration• DNS servers try to resolve a request from a client (though client apps may have their own cache of recently resolved names). If they cannot deal with it directly, then pass it on.• Bind is a standard open source implementation of this software.• DNS and DHCP together link MAC, IP and names. 6
Dynamic DNS & DHCP• In this, client hosts tell DHCP server their hostname & DHCP server tells DNS server.• In theory, means DNS information always correct for host whatever subnet it is plugged into.• But only need to know hostname if it is running services – so it Network Design & Administration should have permanent lease anyway!• Also, security risk – could have host claiming same name as a critical server.• Dynamic DNS is an essential part of MS Active Directory, since AD DS Domain Controllers register themselves to let other machines in AD DS see them.• Within the Internet, dynamic DNS updates have to encrypted to avoid attempted security breaches but dynamic is necessary to allow 7 users to be assigned IP addresses from pool provided by ISP.
Windows Server 2008Editions• Standard• Enterprise• Datacentre• Web Server Network Design & Administration• HPC Server• Itanium• Foundation• Editions are not the same as versions (which normally denote releases).• Editions relate to expected usage. 8
Windows Server Differences Network Design & Administration9
Windows Server Differences Network Design & Administration 10
Why a Server? (Revisited &extended)Why not a desktop machine running Windows 7?Hardware Reasons:• Server hardware needs to be more reliable: Network Design & Administration • Potentially want redundant power supplies, redundant disks (including disk controllers), hot swap memory (not just hot-plug)• Server hardware needs to be extensible: • Need room for more disks, more cards, more memory, more fans … 11
Why a Server?• Servers need more performance: • Tend to have leading edge CPU’s, higher spec network interfaces and associated upgrade options. Network Design & Administration• Servers need to be supported: • Usually business-critical, so need maintenance contracts• Servers need to last longer: • Maintenance contracts, upgrades, spares have to be available for longer 12
Why a Server?• Software is the main reason.• Although desktop operating system has support for most features but normally curtailed in some way.• E.g. Internet Information Services Network Design & Administration • On XP was limited to 10 concurrent connections (it would block HTTP connections) • With Windows 7 / Vista, IIS version 7.5 will queue requests for a limited number of connections at the same time, but connections can be from more machines.• Microsoft Terminal Services limited to one connection at a time (although 3rd party tools provide more connections). 13
Running Servers• Preferably have a clean, lockable environment to keep them in (no dust or coffee in the works and basic security).• Use remote methods to control / monitor (see Network Design & Administration later sessions) but provide local screen / keyboard in case.• Preferably use rack-mount system even if only 1 server in rack) to allow for easy extensibility / replacement. 14• Consider provision of spares pack for quick repair.
Case Study: NTU infrastructure Network Design & Administration 15
Clifton Distribution Network Design & Administration16
Summary of NTU Intranet• 700 Switches and Routers• 400 Servers• 14,000 PC’s Network Design & Administration(approximately)• This is a very big system! Such a system tends to have ‘grown’ and then been occasionally re- engineered rather than built from scratch. 17
Next time & References• Client machines and their relationships to servers. www.samba.org http://technet.microsoft.com/en- Network Design & Administrationus/library/cc781189%28WS.10%29.aspx (Windows Server 2003article) http://www.microsoft.com/en-us/server-cloud/windows-server/2008-r2-editions.aspx http://download.microsoft.com/download/F/C/6/FC6006B5-866E-42C1-88F8-9AC4B8BC610D/WS%20Brand%20Pages%20-%20Editions%20Comparison%20Guide.pdf 18