Lecture 3:More on Servers & ServicesNetwork Design & Administration

Net

wor

k D

esig

n &

Adm

inist

ratio

n

“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

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!• We will cover AD DS in more detail in a future

lecture.

2

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Server Roles: File & Print Servers• Some servers may simply provide file storage.• Some may be used to ease latency in printing (covered in

a later session)• Question:• 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”[1]

3

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Server Role: Windows Internet Name 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 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 secondary's 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

query)[2]

4

Net

wor

k D

esig

n &

Adm

inist

ratio

n

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.• 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

Net

wor

k D

esig

n &

Adm

inist

ratio

n

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.• 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

Net

wor

k D

esig

n &

Adm

inist

ratio

n

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

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 users to be assigned IP addresses from pool provided by ISP.

7

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Windows Server 2008 Editions[3]

• Standard• Enterprise• Datacentre• Web Server• HPC Server• Itanium• Foundation

• Editions are not the same as versions (which normally denote releases).• Editions relate to expected usage.

8

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Windows Server Differences[4]

9

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Windows Server Differences[4]

10

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Why a Server? (Revisited & extended)Why not a desktop machine running Windows 7?Hardware Reasons:• Server hardware needs to be more reliable:• 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

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Why a Server?

• Servers need more performance:• Tend to have leading edge CPU’s, higher spec

network interfaces and associated upgrade options.

• 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

Net

wor

k D

esig

n &

Adm

inist

ratio

n

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• 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

Net

wor

k D

esig

n &

Adm

inist

ratio

n

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

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.• Consider provision of spares pack for quick

repair.

14

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Case Study: NTU infrastructure

15

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Clifton Distribution

16

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Summary of NTU Intranet

• 700 Switches and Routers• 400 Servers• 14,000 PC’s(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

Net

wor

k D

esig

n &

Adm

inist

ratio

n

Next time & References

• Client machines and their relationships to servers.

[1] www.samba.org[2] http://technet.microsoft.com/en-us/library/cc781189%28WS.10%29.aspx (Windows Server 2003 article)[3] http://www.microsoft.com/en-us/server-cloud/windows-server/2008-r2-editions.aspx[4] http://download.microsoft.com/download/F/C/6/FC6006B5-866E-42C1-88F8-9AC4B8BC610D/WS%20Brand%20Pages%20-%20Editions%20Comparison%20Guide.pdf

18