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Network+ Guide to Networks, Fourth Edition
Chapter 13
Ensuring Integrity and Availability
Objectives
• Identify the characteristics of a network that keeps
data safe from loss or damage
• Protect an enterprise-wide network from viruses
• Explain network- and system-level fault-tolerance
techniques
• Discuss issues related to network backup and
recovery strategies
• Describe the components of a useful disaster
recovery plan and the options for disaster
contingencies
What Are Integrity and Availability?
• Integrity: soundness of network’s programs, data,
services, devices, and connections
• Availability: how consistently and reliably file or
system can be accessed by authorized personnel
– Need well-planned and well-configured network
– Data backups, redundant devices, protection from
malicious intruders
• Phenomena compromising integrity and availability:
– Security breaches, natural disasters, malicious intruders,
power flaws, human error
What Are Integrity and Availability?
• General guidelines for protecting network:
– Allow only network administrators to create or modify
NOS and application system files
– Monitor network for unauthorized access or changes
– Record authorized system changes in a change
management system
– Install redundant components
– Perform regular health checks
What Are Integrity and Availability?
(continued)
• General guidelines for protecting network
(continued):
– Check system performance, error logs, and system log
book regularly
– Keep backups, boot disks, and emergency repair disks
current and available
– Implement and enforce security and disaster recovery
policies
Viruses
• Program that replicates itself with intent to infect
more computers
– Through network connections or exchange of external
storage devices
– Typically copied to storage device without user’s
knowledge
• Trojan horse: program that disguises itself as
something useful but actually harms system
– Not considered a virus
Types of Viruses
• Boot sector viruses: located in boot sector of
computer’s hard disk
– When computer boots up, virus runs in place of
computer’s normal system files
– Removal first requires rebooting from uninfected, writeprotected disk with system files on it
• Macro viruses: take form of macro that may be
executed as user works with a program
– Quick to emerge and spread
– Symptoms vary widely
Types of Viruses (continued)
• File-infected viruses: attach to executable files
– When infected executable file runs, virus copies itself to
memory
– Can have devastating consequences
– Symptoms may include damaged program files,
inexplicable file size increases, changed icons for
programs, strange messages, inability to run a program
• Worms: programs that run independently and travel
between computers and across networks
– Not technically viruses
– Can transport and hide viruses
Types of Viruses (continued)
• Trojan horse: program that claims to do something
useful but instead harms system
• Network viruses: propagated via network protocols,
commands, messaging programs, and data links
• Bots: program that runs automatically, without
requiring a person to start or stop it
– Many bots spread through Internet Relay Chat (IRC)
– Used to damage/destroy data or system files, issue
objectionable content, further propagate virus
Virus Characteristics
• Encryption: encrypted virus may thwart antivirus
program’s attempts to detect it
• Stealth: stealth viruses disguise themselves as
legitimate programs or replace part of legitimate
program’s code with destructive code
• Polymorphism: polymorphic viruses change
characteristics every time transferred
• Time-dependence: time-dependent viruses
programmed to activate on particular date
Virus Protection: Antivirus Software
• Antivirus software should at least:
– Detect viruses through signature scanning
– Detect viruses through integrity checking
– Detect viruses by monitoring unexpected file changes or
virus-like behaviors
– Receive regular updates and modifications from a
centralized network console
– Consistently report only valid viruses
• Heuristic scanning techniques attempt to identify viruses by
discovering “virus-like” behavior (may give “false positives”)
Antivirus Policies
• Provide rules for using antivirus software and
policies for installing programs, sharing files, and
using floppy disks
• Suggestions for antivirus policy guidelines:
– Every computer in organization equipped with virus
detection and cleaning software
– Users should not be allowed to alter or disable antivirus
software
– Users should know what to do in case virus detected
Antivirus Policies (continued)
• Suggestions for antivirus policy guidelines
(continued):
– Antivirus team should be appointed to focus on
maintaining antivirus measures
– Users should be prohibited from installing any
unauthorized software on their systems
– Systemwide alerts should be issued to network users
notifying them of serious virus threats and advising them
how to prevent infection
Virus Hoaxes
• False alerts about dangerous, new virus that could
cause serious damage to systems
– Generally an attempt to create panic
– Should not be passed on
– Can confirm hoaxes online
Fault Tolerance
• Capacity for system to continue performing despite
unexpected hardware or software malfunction
• Failure: deviation from specified level of system
performance for given period of time
• Fault: involves malfunction of system component
– Can result in a failure
• Varying degrees
– At highest level, system remains unaffected by even most
drastic problems
Environment
• Must analyze physical environment in which devices
operate
– e.g., excessive heat or moisture, break-ins, natural
disasters
• Can purchase temperature and humidity monitors
– Trip alarms if specified limits exceeded
Power: Power Flaws
• Power flaws that can damage equipment:
– Surge: momentary increase in voltage due to lightning
strikes, solar flares, or electrical problems
– Noise: fluctuation in voltage levels caused by other
devices on network or electromagnetic interference
– Brownout: momentary decrease in voltage; also known as
a sag
– Blackout: complete power loss
UPSs (Uninterruptible Power Supplies)
• Battery-operated power source directly attached to
one or more devices and to power supply
– Prevents undesired features of outlet’s A/C power from
harming device or interrupting services
– Standby UPS: provides continuous voltage to device
• Switch to battery when power loss detected
– Online UPS: uses power from wall outlet to continuously
charge battery, while providing power to network device
through battery
UPSs (continued)
• Factors to consider when deciding on a UPS:
– Amount of power needed
• Power measured in volt-amps
– Period of time to keep a device running
– Line conditioning
– Cost
Generators
Figure 13-2: UPSs and a generator in a network design
Topology and Connectivity
• Key to fault tolerance in network design is supplying
multiple possible data paths
– If one connection fails, data can be rerouted
– On LANs, star topology and parallel backbone provide
greatest fault tolerance
– On WANs, full mesh topology offers best fault tolerance
– SONET networks highly fault-tolerant
• Redundancy in network offers advantage of
reducing risk of lost functionality and profits from
network faults
Topology and Connectivity (continued)
Figure 13-3: VPNs linking multiple customers
Topology and Connectivity (continued)
• Automatic fail-over: use redundant components able
to immediately assume duties of an identical
component in event of failure or fault
• Can provide some level of fault tolerance by using
hot swappable parts
• Leasing redundant T1s allows for load balancing
– Automatic distribution of traffic over multiple links or
processors to optimize response
Topology and Connectivity (continued)
Figure 13-5: Fully redundant T1 connectivity
Servers
• Make servers more fault-tolerant by supplying them
with redundant components
– NICs, processors, and hard disks
– If one item fails, entire system won’t fail
– Enable load balancing
Server Mirroring
• Mirroring: one device or component duplicates
activities of another
• Server Mirroring: one server duplicates transactions
and data storage of another
–
–
–
–
Must be identical machines using identical components
Requires high-speed link between servers
Requires synchronization software
Form of replication
• Servers can stand side by side or be positioned in
different locations
Clustering
• Link multiple servers together to act as single server
– Share processing duties
– Appear as single server to users
– If one server fails, others automatically take over data
transaction and storage responsibilities
– More cost-effective than mirroring
– To detect failures, clustered servers regularly poll each
other
– Servers must be close together
Storage: RAID (Redundant Array of Independent Disks)
• Collection of disks that provide fault tolerance for
shared data and applications
– Disk array
– Collection of disks that work together in RAID
configuration, often referred to as RAID drive
• Appear as single logical drive to system
• Hardware RAID: set of disks and separate disk
controller
– Managed exclusively by RAID disk controller
• Software RAID: relies on software to implement and
control RAID techniques
RAID Level 0―Disk Striping
• Simple implementation of RAID
– Not fault-tolerant
– Improves performance
Figure 13-6: RAID Level 0—disk striping
RAID Level 1—Disk Mirroring
• Data from one disk copied to another disk
automatically as information written
– Dynamic backup
– If one drive fails, disk array controller automatically
switches to disk that was mirroring it
– Requires two identical disks
– Usually relies on system software to perform mirroring
• Disk duplexing: similar to disk mirroring, but
separate disk controller used for each disk
RAID Level 1—Disk Mirroring (continued)
Figure 13-7: RAID Level 1—disk mirroring
RAID Level 3—Disk Striping with Parity ECC
• Disk striping with special error correction code
(ECC)
– Parity: mechanism used to verify integrity of data by
making number of bits in a byte sum to either an odd or
even number
•
•
•
•
Even parity or odd parity
Tracks integrity of data on disk
Parity bit assigned to each data byte when written to disk
When data read, data’s bits plus parity bit summed (parity should
match)
RAID Level 3—Disk Striping with Parity ECC
Figure 13-8: RAID Level 3—disk striping with parity ECC
RAID Level 5—Disk Striping with Distributed Parity
• Data written in small blocks across several disks
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–
–
–
Parity error checking information distributed among disks
Highly fault-tolerant
Very popular
Failed disk can be replaced with little interruption
• Hot spare: disk or partition that is part of array, but
used only in case a RAID disks fails
• Cold spare: duplicate component that can be
installed in case of failure
RAID Level 5—Disk Striping with Distributed Parity
Figure 13-9: RAID Level 5—disk striping with distributed parity
NAS (Network Attached Storage)
• Specialized storage device that provides centralized
fault-tolerant data storage
– Maintains own interface to LAN
– Contains own file system optimized for saving and
serving files
– Easily expanded without interrupting service
– Cannot communicate directly with network clients
NAS (continued)
Figure 13-10: Network attached storage on a LAN
SANs (Storage Area Networks)
Figure 13-11: A storage area network
Data Backup
• Copy of data or program files created for archiving
or safekeeping
– No matter how reliable and fault-tolerant you believe your
server’s hard disk (or disks) to be, still risk losing
everything unless you make backups on separate media
and store them off-site
• Many options exist for making backups
Backup Media and Methods
• To select appropriate solution, consider following
questions:
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Sufficient storage capacity?
Reliability?
Data error checking techniques?
System efficient enough to complete backup process
before daily operations resume?
Cost and capacity?
Compatibility?
Frequent manual intervention?
Scalability?
Optical Media
• Capable of storing digitized data
– Uses laser to write and read data
– CD-ROMs and DVDs
• Requires proper disk drive to write data
• Writing data usually takes longer than saving data to
another type of media
Tape Backups
• Relatively simple, capable of storing large amounts
of data, at least partially automated
• On relatively small networks, standalone tape drives
may be attached to each server
• On large networks, one large, centralized tape
backup device may manage all subsystems’ backups
– Usually connected to computer other than file server
External Disk Drives
• Storage devices that can be attached temporarily to a
computer via USB, PCMCIA, FireWire, or
Compact-Flash port
– Removable disk drives
• For backing up large amounts of data, likely to use
external disk drive with backup control features,
high capacity, and fast read-write access
• Faster data transfer rates than optical media or tape
backups
Network Backups
• Save data to another place on network
– Must back up data to different disk than where it was
originally stored
• Most NOSs provide utilities for automating and
managing network backups
• Online backup: saves data across Internet to another
company’s storage array
– Strict security measures to protect data in transit
– Backup and restoration processes automated
Backup Strategy
• Strategy should address following questions:
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What data must be backed up?
Rotation schedule?
Time backups occur?
Method of accuracy verification?
Where and how long will backup media be stored?
Who will take responsibility?
How long will backups be saved?
Where will documentation be stored?
Backup Strategy (continued)
• Archive bit: file attribute that can be checked or
unchecked
– Indicates whether file must be archived
• Backup methods use archive bit in different ways
– Full backup: all data copied to storage media, regardless
of whether data is new or changed
• Archive bits set to “off” for all files
– Incremental backup: copies only data that has changed
since last full or incremental backup
• Unchecks archive bit for every file saved
– Differential backup: does not uncheck archive bits for
files backed up
Backup Strategy (continued)
• Determine best possible backup rotation scheme
– Provide excellent data reliability without overtaxing
network or requiring a lot of intervention
– Several standard backup rotation schemes
• Grandfather-father-son: Uses DAILY (son), weekly (father), and
monthly (grandfather) backup sets
• Make sure backup activity recorded in backup log
• Establish regular schedule of verification
Backup Strategy (continued)
Figure 13-13: The “grandfather-father-son” backup rotation scheme
Disaster Recovery Planning
• Disaster recovery: process of restoring critical
functionality and data after enterprise-wide outage
• Disaster recovery plan accounts for worst-case
scenarios
– Contact names and info for emergency coordinators
– Details on data and servers being backed up, backup
frequency, backup location, how to recover
– Details on network topology, redundancy, and agreements
with national service carriers
– Strategies for testing disaster recovery plan
– Plan for managing the crisis
Disaster Recovery Contingencies
• Several options for recovering from disaster
– Cold site: place where computers, devices, and
connectivity necessary to rebuild network exist
• Not configured, updated, or connected
– Warm site: same as cold site, but some computers and
devices appropriately configured, updated, or connected
– Hot site: computers, devices, and connectivity necessary
to rebuild network are appropriately configured, updated,
and connected to match network’s current state
Summary
• Integrity refers to the soundness of your network’s
files, systems, and connections
• Several basic measures can be employed to protect
data and systems on a network
• A virus is a program that replicates itself so as to
infect more computers, either through network
connections or through external storage devices
passed among users
• A good antivirus program should be able to detect
viruses through signature scanning, integrity
checking, and heuristic scanning
Summary (continued)
• The goal of fault-tolerant systems is to prevent faults
from progressing to failures
• Fault tolerance is a system’s capacity to continue
performing despite an unexpected hardware or
software malfunction
• A UPS is a battery power source that prevents
undesired features of the power source from harming
the device or interrupting its services
• For utmost fault tolerance in power supply, a
generator is necessary
Summary (continued)
• Critical servers often contain redundant NICs,
processors, and/or hard disks to provide better fault
tolerance
• Server mirroring involves utilizing a second,
identical server to duplicate the transactions and data
storage of one server
• Clustering links multiple servers together to act as a
single server
• RAID is an important storage redundancy feature
Summary (continued)
• Backups can be saved to optical media (such as CDs
and DVDs), tapes, external disk drives, or to another
location on a network
• The aim of a good backup rotation scheme is to
provide excellent data reliability but not to overtax
your network or require much intervention
• Disaster recovery is the process of restoring your
critical functionality and data after an enterprisewide outage that affects more than a single system or
a limited group of users