Download pt08_2008 - Carl Rebman Associate Professor of Information

Business Data Communications
Chapter Eight
Servers in the Enterprise
Primary Learning Objectives
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Differentiate between clients and servers
Describe five server physical components
Identify major server types
Understand the concept of well-known ports
Explain server clustering
Define “system area network”
Clients and Servers
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Networks commonly make use of both clients and
servers:
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Clients request networked resources from servers
Servers manage and distribute networked resources to
clients
Clients and servers both have operating systems
that differentiate them from each other
Modern client operating systems are network-aware
Server operating systems are specialized
Clients and Servers
Client and Server Software
Server Physical Components
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A server has a variety of physical components
Five physical components particularly important to
a server’s performance are:
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Physical case
Memory
Processor
Drive interface
Network Interface Card
Physical Case
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A client desktop’s physical case is usually kept to a
minimal size as it occupies and shares space in a
user’s work environment
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The case occupies a “footprint”
Servers are typically secured and locked away, with
infrequent physical access by staff:
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Therefore, a server’s footprint can be larger than a client’s
The server’s physical case is often more rugged
The server’s physical case is referred to as its chassis
Physical Case
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A larger server physical chassis:
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Allows technicians more room for working within the
chassis
Facilitates upgrading the server
Provides more bays for expansion
Offers more space for additional components
Allows for a larger and more robust power supply
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A server may require a redundant power supply, as well as
its own internal power surge protector
Physical Case
Intel Server Chassis SC5250-E:
Has four fixed-drive bays and
supports up to five hot-swap SCSI or
four hot-swap SATA hard-drive bays.
This chassis allows adding more
storage without having to take the
server offline.
Expansion cards can be easily added
due to the tool-free access enabled
by thumb screws on side panels.
Memory
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Memory is also called RAM, for random access
memory
RAM “sticks” plug into slots housed on a server
computer’s motherboard
Servers generally support much higher capacities of
RAM than do clients
A server’s RAM slots are often able to support
higher capacity RAM sticks than a client’s
Memory
Processor
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A server’s processor is also called a CPU, for central
processing unit
The CPU is the workhorse of the server and is
critical for processing of instructions and data
Server motherboards often support multiple CPUs
If a server has multiple CPUs, its server operating
system (SOS) must be able to support the number
configured
If multiple CPUs are used, the SOS must be capable
of managing the CPUs that reference each other’s
cache
Processor
An INTEL
server
motherboard,
model
S845WD1-E
Drive Interface
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Servers usually support more drives than does a
typical client device
Drives include:
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Floppy
Tape
CD
Hard drive
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Hard drives, in particular, are a key server component
Drives require an interface to the server’s CPU
Drive Interface
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Two common drive interfaces are:
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IDE – Integrated Drive Electronics
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Is used mostly by clients
Requires a controller
SCSI – Small Computer System Interface
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Is used mostly by servers
Requires a controller
The SCSI controller is often an adapter card that plugs into a
motherboard’s expansion slot
The SCSI adapter card uses a parallel bus to communicate
with devices connected to the parallel bus
The SCSI adapter can support up to 15 internal and/or
external devices
Drive Interface
Network Interface Card – NIC
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Critical server NIC considerations include:
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Throughput capacity
Half- or full-duplex communications
Direct memory access (DMA)
Bus mastering
Buffers
On-board processor
Major Types of Servers
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If a resource needs to be shared or managed, a
server can likely be configured to do it
Many types of servers are possible, including:
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File and application
Database
Web, e-mail, and FTP
Domain Name System (DNS)
Dynamic Host Configuration Protocol (DHCP)
File and Application
Servers
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Having duplicate files and applications on multiple
devices raises numerous questions, including:
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Who has the most current version of the file or
application?
How can multiple copies be adequately secured?
How many copies have been distributed?
Who maintains these multiple copies?
File and application servers allow for centralized
management, control, and distribution
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Users are typically authenticated before being given
access to networked file and application resources
File and Application
Servers
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Must be fast and reliable
Require sufficient storage to accommodate user needs
Are often implemented in software
File servers transmit the entire file from the server to the
client:
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For small files this may be suitable
For large files this may result in a server bottleneck
Application servers control applications, using two
components:
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The client front-end
The server back-end
File and Application
Servers
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Licensing is an additional legal and ethical
consideration when sharing files and applications
across the network
Three forms of licensing are:
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Individual
Metered
Site
For a file or application to be distributed across a
network, it must be network-compatible
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Not all applications, nor other resources, can be shared
Database Servers
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Provide management access control software that
makes database records available to users across
the network
In most implementations, perform much of the
processing, with only the result being transmitted
to the client
As with application servers, require a client frontend process and a server back-end process
Allow for distributed databases
Database Server
Web, E-mail, and FTP Servers
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A Web server runs application layer TCP/IP
protocols
A client accessing a Web server utilizes a browser
Web pages hosted on a Web server are expressed
using HTML – HyperText Markup Language
Two popular Web server programs are:
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Apache – an open system program
Internet Information Server (IIS) – a Microsoft program
Web, E-mail, and FTP Servers –
Well-known Ports
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Requests come to a Web server through “ports”
These ports are logical designations that represent
a particular type of requested service
Port values are also called “well-known ports”
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The most common port used by a client Web browser is
well-known port 80
Well-known ports are primary targets by hackers
Many application layer server requests have been
standardized to use particular well-known ports
Web, E-mail, and FTP Servers –
A few Well-known Ports
Web, E-mail, and FTP Servers
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A client request is initiated through a Uniform
Resource Locator, or URL
For most users of a Web server the URL takes the
form of a World Wide Web (WWW) address:
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www.woodbury.edu
A URL has four parts:
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The protocol (HTTP or FTP, for example)
The server’s IP or Domain Name System address
An optional port number
The directory or file being requested
Web, E-mail, and FTP Servers
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Popular e-mail Web server protocols include:
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SMTP – Simple Mail Transfer Protocol
POP3 – Post Office Protocol version 3
IMAP – Internet Message Access Protocol
A single physical mail server might be running
multiple logical mail services
FTP provides for transfer of files from a server to a
client, and vice-versa
Whether Web, e-mail, or FTP, a client component
and a server component must both be configured
Domain Name System (DNS)
Servers
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DNS servers are critical in a TCP/IP network
DNS servers resolve logical IP network layer
addresses to logical application layer domain name
addresses
The DNS system is designed around a hierarchy of
domains:
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There are top- and second-level domains
A domain can have subdomains
A domain name is resolved when the DNS server matches
a host’s IP address to a domain name address
Domain Name System (DNS)
Servers
Clients must
be configured
to know who
their DNS
server is.
A redundant
DNS server
can be
specified.
Domain Name System (DNS)
Hierarchy
Dynamic Host Configuration Protocol
(DHCP) Servers
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Clients in a TCP/IP network must be configured to
know their logical network layer IP address
This IP address can be manually configured or
automatically configured using software:
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In a small enterprise, manual configuration is often
practical
In a large enterprise, with hundreds or thousands of
clients, manual configuration is not practical
DHCP servers are used primarily to automate a client IP
addressing configuration
Dynamic Host Configuration Protocol
(DHCP) Servers
This Windows
client has been
configured so
that DHCP has
been
automatically
enabled.
Proxy Servers
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Are used primarily to provide increased security:
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A “proxy” literally means authorization to act on behalf of
another
A proxy server:
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Intercepts an internal networked client’s request
Attaches its own IP address to that request
Hands the request out to the external world, so that the
external world sees the address of the proxy, not the address
of the originating client
Reverses the above process when requested resources are
returned
Maintains an address list of which internal client is making
what request
Is often used in conjunction with a firewall
Proxy Servers
Server Clusters
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Connect multiple physical servers into a single
logical group:
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To clients accessing the server cluster, the servers in the
cluster appear to be one single server
Servers in the cluster can share their workload, resulting in
load balancing of network traffic
Should one of the servers in the cluster fail, other servers
in the cluster can take over its duties
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This is called failover capability
Servers in a cluster must have a server operating system
that supports clustering
Server clusters are highly scalable
Server Clusters
System Area Networks
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Are a local network designed for high-speed
interconnection in cluster environments
Almost exclusively use a “switched fabric”
technology:
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A switched fabric refers to the way that physical ports
within a switch are linked, allowing the ports to
communicate and transfer data amongst themselves
Fibre Channel, a switching fabric implementation, is
particularly associated with System Area Networks
In summary
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Servers play a critical role in the enterprise
Important server components typically include:
case, memory, processors, drive interface, and
Network Interface Cards
Common types of servers include: file, application,
database, Web, e-mail, FTP, DNS, and DCHP
Server clustering allows the grouping of multiple
physical servers into a single logical group
System Area Networks are one way in which server
clusters are being implemented