Network+ Guide to Networks, Fourth Edition

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