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- Ensuring Integrity and Availability
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- Identify the characteristics of a network that keep 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
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- Integrity
- Soundness of a network’s programs, data, services, devices, and
connections
- Availability
- Refers to how consistently and reliably a file system to be accessed by
authorized personnel
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- Prevent anyone other than a network administrator from opening or
changing the system files
- Monitor the network for unauthorized access or change
- Process of monitoring a network for unauthorized access to its devices
is known as intrusion detection
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- Record authorized system changes in a change management system
- Install redundant components
- Situation in which more than one component is installed and ready to
use for storing, processing, or transporting data is referred to as redundancy
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- Perform regular health checks on the network
- Monitor system performance, error logs, and the system log book
regularly
- Keep backups, boot disks, and emergency repair disks current and
available
- Implement and enforce security and disaster recovery policies
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- Virus
- Program that replicates itself so as to infect more computers
- Trojan horse
- Disguises itself as something useful but actually harms your system
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- Boot sector viruses
- Reside on the boot sector of a floppy disk and become transferred to
the partition sector or the DOS boot sector on a hard disk
- Macro Viruses
- Take the form of a word-processing or spreadsheet program macro
- File infected viruses
- Attach themselves directly to executable files
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- Network viruses
- Propagate themselves via network protocols, commands, messaging
programs, and data links
- Worms
- Technically not viruses, but rather programs that run independently and
travel between computers across networks
- Trojan horse
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- Encryption
- Stealth
- Polymorphism
- Time-dependence
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- Symptoms of a virus
- Unexplained increases in file sizes
- Programs launching, running, or exiting more slowly than usual
- Unusual error messages appearing without probable cause
- Significant, unexpected loss of system memory
- Fluctuations in display quality
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- Functions your antivirus software should perform
- Signature scanning
- Comparison of a file’s content with known virus signatures in a
signature database
- Integrity checking
- Method of comparing current characteristics of files and disks against
an archived version of these characteristics to discover any changes
- It should detect viruses by monitoring unexpected file changes or
virus-like behaviors
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- Functions your antivirus software should perform (cont.)
- Receive regular updates and modifications from a centralized network
console
- Consistently report only valid viruses, rather than reporting “false
alarms”
- Heuristic scanning
- Attempt to identify viruses by discovering “virus-like” behavior
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- General guidelines for an antivirus policy
- Every computer in an organization should be equipped with virus
detection and cleaning software that regularly scans for viruses
- Users should not be allowed to alter or disable the antivirus software
- Users should know what to do in case their antivirus program detects a
virus
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- General guidelines for an antivirus policy (cont.)
- Every organization should have an antivirus team that focuses on
maintaining the antivirus measures in place
- Users should be prohibited from installing any unauthorized software on
their systems
- Organizations should impose penalties on users who do not follow the
antivirus policy
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- False alert about a dangerous, new virus that could cause serious damage
to your workstation
- Usually have no realistic basis and should be ignored
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- Capacity for a system to continue performing despite an unexpected
hardware or software malfunction
- Failure
- Deviation from a specified level of system performance for a given
period of time
- Fault
- Involves the malfunction of one component of a system
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- Fail-over
- Process of one component immediately assuming the duties of an
identical component
- A sophisticated means for dynamically replicating data over several
physical hard drives is known as hard disk redundancy, called RAID (for Redundant
Array of Inexpensive Disks)
- To assess the fault tolerance of your network, you must identify any
single point of failure
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- Environment
- Analyze the physical environments in which your devices operate
- Power
- Whatever the cause, networks cannot tolerate power loss or less than
optimal power
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- Surge
- Line noise
- Brownout
- Blackout
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- Battery-operated power source directly attached to one or more devices
and to a power supply
- Standby UPS
- Switches instantaneously to the battery when it detects a loss of power
from the wall outlet
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- Online UPS
- Uses the A/C power from the wall outlet to continuously charge its
battery, while providing power to a network device through its battery
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- Amount of power needed
- A volt-amp (VA) is the product of the voltage and current of the
electricity on a line
- Period of time to keep a device running
- Line conditioning
- Cost
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- If your organization cannot withstand a power loss of any duration,
consider investing in an electrical generator for your building
- Generators do not provide surge protection, but do provide clean (free
from noise) electricity
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- Hot swappable
- Identical components that automatically assume the functions of their
counterpart if one suffers a fault
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- Load balancing
- Automatic distribution of traffic over multiple links or processors to
optimize response
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- Server mirroring
- Fault tolerance technique in which one server duplicates the
transactions and data storage of another
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- Fault-tolerance technique that links multiple servers together to act as
a single server
- Clustered servers share processing duties and appear as a single server
to users
- Clustering is more cost-effective than mirroring
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- Redundant Array of Inexpensive Disks (RAID)
- Collection of disks that provide fault tolerance for shared data and
applications
- A group of hard disks is called a disk array
- The collection of disks working together in a RAID configuration is
often referred to as the “RAID drive”
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- Simple implementation of RAID in which data are written in 64 KB blocks
equally across all disks in the array
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- Data from one disk are copied to another disk automatically as the
information is written
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- Disk stripping with a special type of error correction code (ECC)
- Term parity refers to the mechanism used to verify the integrity of data
by making the number of bits in a byte sum to either an odd or even
number
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- Parity error checking
- Process of comparing the parity of data read from disk with the type of
parity used by the system
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- Data are written in small blocks across several disks
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- Specialized storage device or group of storage devices providing
centralized fault-tolerant data storage for a network
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- Distinct networks of storage devices that communicate directly with each
other and with other networks
- Extremely fault tolerant
- Extremely fast
- Much of their speed can be attributed to Fibre Channel
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- Copy of data or program files created for archiving purposes
- Without backing up data and storing them off-site, you risk losing
everything
- Note that backing up workstations or backing up servers and other host
systems are different operations
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- Most popular method for backing up networked systems
- Vault
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- Questions to ask when selecting the appropriate tape backup solution for
your network:
- Does the backup drive and/or media provide sufficient storage capacity?
- Are the backup software and hardware proven to be reliable?
- Does the backup software use data error checking techniques?
- Is the system quick enough to complete the backup process before daily
operations resume?
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- Questions to ask when selecting the appropriate tape backup solution for
your network (cont.):
- How much do the tape drive, software, and media cost?
- Will the backup hardware and software be compatible with existing
network hardware and software?
- Does the backup system require frequent manual intervention?
- Will the backup hardware, software, and media accommodate your
network’s growth?
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- Online backups
- Questions to ask in developing a backup strategy:
- What kind of rotation schedule will backups follow?
- At what time of day or night will the backups occur?
- How will you verify the accuracy of the backups?
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- Questions to ask in developing a backup strategy (cont.):
- Where will backup media be stored?
- Who will take responsibility for ensuring that backups occurred?
- How long will you save backups?
- Where will backup and recovery documentation be stored?
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- Full backup
- All data on all servers are copied to a storage medium
- Incremental backup
- Only data that have changed since the last backup are copied to a
storage medium
- Differential backup
- Only data that have changed since the last backup are copied to a
storage medium, and that information is then marked for subsequent
backup
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- Specifies when and how often backups will occur
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51
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- Process of restoring critical functionality and data after
enterprise-wide outage that affects more than a single system or limited
group of users
- Must take into account the possible extremes, rather than relatively
minor situations
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- Contact names for emergency coordinators who will execute the disaster
recovery response
- Details on which data and servers are being backed up, how frequently
backups occur, where backups are kept, and how backup data can be
recovered in full
- Details on network topology, redundancy, and agreements with national
service carriers
- Regular strategies for testing the disaster recovery plan
- Plan for managing the crisis
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- Integrity refers to the soundness of your network’s files, systems, and
connections
- Availability of a file or system refers to how consistently and reliably
it can be accessed by authorized personnel
- 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
- In broad terms, a failure is a deviation from a specified level of
system performance for a given period of time
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- Fault tolerance is a system’s capacity to continue performing despite an
unexpected hardware or software malfunction
- Networks cannot tolerate power loss or less than optimal power
- Type of network topology that offers the best fault tolerance is a mesh
topology
- A backup is a copy of data or program files created for archiving or
safekeeping purposes
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- Have a strategy for backup
- Different backup methods provide varying levels of certainty and
corresponding labor and cost
- Disaster recovery is the process of restoring critical functionality and
data after an enterprise-wide outage that affects more than a single
user or limited group of users
- Every organization should have a disaster recovery team and disaster
recovery plan
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