1. Network+ Guide to Networks, Fourth Edition
Chapter 13
Ensuring Integrity and Availability

2. 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
Network+ Guide to Networks, 4e

3. 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
Network+ Guide to Networks, 4e

4. 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, write-protected 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
Network+ Guide to Networks, 4e

5. 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
Network+ Guide to Networks, 4e

6. 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
Network+ Guide to Networks, 4e

7. 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
Network+ Guide to Networks, 4e

8. 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”)
Network+ Guide to Networks, 4e

9. 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
Network+ Guide to Networks, 4e

10. 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
Network+ Guide to Networks, 4e

11. 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
Network+ Guide to Networks, 4e

12. 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
Network+ Guide to Networks, 4e

13. 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
Network+ Guide to Networks, 4e

14. 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
Network+ Guide to Networks, 4e

15. 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
Network+ Guide to Networks, 4e

16. Storage: RAID (Redundant Array of Independent (or Inexpensive) 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
Network+ Guide to Networks, 4e

17. RAID Level 0―Disk Striping
Simple implementation of RAID
Not fault-tolerant
Improves performance
Figure 13-6: RAID Level 0—disk striping
Network+ Guide to Networks, 4e

18. 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
Network+ Guide to Networks, 4e

19. RAID Level 1—Disk Mirroring (continued)
Figure 13-7: RAID Level 1—disk mirroring
Network+ Guide to Networks, 4e

20. RAID Level 5—Disk Striping with Distributed Parity
Data written in small blocks across several disks
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
Network+ Guide to Networks, 4e

21. RAID Level 5—Disk Striping with Distributed Parity (continued)
Figure 13-9: RAID Level 5—disk striping with distributed parity
Network+ Guide to Networks, 4e

22. 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
Network+ Guide to Networks, 4e

23. NAS (continued) Figure 13-10: Network attached storage on a LAN
Network+ Guide to Networks, 4e

24. SANs (Storage Area Networks)
Figure 13-11: A storage area network
Network+ Guide to Networks, 4e

25. 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
Network+ Guide to Networks, 4e

26. 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
Network+ Guide to Networks, 4e

27. 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+ Guide to Networks, 4e

28. 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
Network+ Guide to Networks, 4e

29. Disaster Recovery: 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
Network+ Guide to Networks, 4e

30. 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
Network+ Guide to Networks, 4e