Layered architecture

• Shows how communication should take place
• Clarify the general functions of a communication process
• To break down complex networking processes into more manageable sub-layers
• Using industry standard interfaces enables interoperability
• To change the features of one layer without changing the code in every layer
• Easier troubleshooting

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Open Systems Interconnect (OSI) Model

Layer 7 – Application

• Responsible for all application-to-application communications
• User information maintained at this layer is user data
• Security: Confidentiality, Authentication, Data Integrity, Non-repudiation
• Technology: Gateways
• Protocols: FTP, SMB, Telnet, TFTP, SMTP, HTTP, NNTP, CDP, GOPHER, SNMP, NDS, AFP, SAP, NCP, SET

Layer 6 – Presentation

• Responsible for the formatting of the data so that it is suitable for presentation
• Responsible for character conversion (ASCII/EBCDIC)
• Encryption/Decryption, Compressions and Virtual Terminal Emulation
• User information maintained at this layer is called messages
• Security: Confidentiality, Authentication, Encryption
• Technology: Gateway
• Protocols: ASCII, EBCDIC, Postscript, JPEG, MPEG, GIF

Layer 5 – Session

• Responsible for the setup of the links, maintaining of the link and the link tear-down between applications
• Security: None
• Technology: Gateway
• Protocols: Remote Procedure Calls (RPC), SQL, RADIUS, DNS, ASP

Layer 4 – Transport

• Responsible for the guaranteed delivery of user information
• Also responsible for error detection, correction and flow control
• User information at this layer is called datagram
• Security: Confidentiality, Authentication, Integrity
• Technology: Gateway
• Protocols: TCP, UDP, SSL, SSH-2, SPX, NetBIOS, ATP

Layer 3 – Network

• Responsible for the routing of user data from one node to another through the network including the path selection
• Logical addresses are used at this layer
• User information maintained at this layer is called packets
• Security: Confidentiality, Authentication, Data Integrity
• Technology: Virtual Circuits (ATM), routers
• Protocols: IP, IPX, ICMP, OSPF, IGRP, EIGRP, RIP, BOOTP, DHCP, ISIS, ZIP, DDP, X.25

Layer 2 – Data Link

• Responsible for the physical addressing of the network via MAC addresses
• There are two sublevels: MAC & LLC
• Has error detection, frame ordering and flow control
• User information maintained at this layer is called frames
• Security: Confidentiality
• Technology: Bridges, switches
• Protocols: L2F, PPTP, L2TP, PPP, SLIP, ARP, RARP, SLARP, IARP, SNAP, BAP, CHAP, LCP, LZS, MLP, Frame Relay, Annex A, Annex D, HDLC, BPDU, LAPD, ISL, ,MAC, Ethernet, Token Ring, FDDI

Layer 1 – Physical

• Responsible for the physical transmission of the binary digits through the physical medium
• Includes things such as the physical cables, interfaces and data rate specifications
• User information maintained at this layer is called bits
• Security: Confidentiality
• Technology: ISDN, Hubs, Repeaters, Cables

Anyway…

This week’s Yeah Boy! (should have been last week, but who’s tracking?)…

Efren Peñaflorida and the rest of the 10 CNN 2009 Heroes. Their stories are simply the true silver lining in the dark clouds that has been laying over our dear planet. Efren Peñaflorida was named the CNN Hero of the Year, but even though I am truly proud of this man from my home country, I can easily say that any of the other 9 folks recognized in this event are equally deserving.

My hat’s off to these heroes: http://www.cnn.com/SPECIALS/cnn.heroes/archive09/index.html

What else is there to say but YEAH BOY!!!

This week’s Yah Suck, well there are so many choices:

1. The publicity-craving-I-want-my-15-minutes-of-fame-damn-the-fucking-security-and-dignity-of-our-nation  Salahi’s… I saw an interview of these Whitehouse party crashers and they said: “This event has totally ruined our lives.” Well, if you weren’t so egotistically-inept did you ever think that you will get away with breaching the security of the home of the President of the United States? You crash the party of celebrities, you are bound to get sued for tresspassing, and you wonder why you are getting so much flack for crashing the Whitehouse? You are not only STOOPID, but also YAH SUCK!!!

2. The 3 Secret Service officers who failed to follow protocol and let the Salahi’s talk their way into the Whitehouse…. Dude, dude, DUDE!!! YAH SUCK!!!

3.Tiger Woods… Dude, sorry but you got caught, so YAH SUCK!!!

4. The Lamestream Media who thrive in sensationalizing the “imperfections” of celebrities… Seriously, don’t you have other more real-earth-changing/shattering news to cover than to waste 15 minutes of the news hour on a man who despite what many claims is also human and bound to make really bad decisions just like the rest of us… I know that he is a celebrity and that if he is ever caught peeing in public, its news… BUT CHEEZE-WHIZ-CRY-ME, HE IS NOT THE ONLY NEWS!!! We are still fighting 2 wars, our economy is actually showing a little bit of life, our healthcare is in the hands of a few inept well-insured politicians, people are doing great things despite all odds and you will devote so much time of your news segment on some man’s infidelity? YAH SUCK!!!

5. The Network Gremlins I had to battle most of the week and particularly early this morning. Just gotta put this in because seriously it has been a pain… To all Network Gremlins out there who ruins IT Geeks day by causing havoc for no apparent or explanable reason, YAH SUCK!!!

For example: In 2000 Amazon, CNN, eBay, and Yahoo! were victims of a DoS attack.

Fault Tolerance is the ability of a system to respond gracefully to an unexpected hardware or software failure. There are many levels of fault tolerance, the lowest being the ability to continue operation in the event of a power failure. Many fault-tolerant computer systems mirror all operations — that is, every operation is performed on two or more duplicate systems, so if one fails the other can take over. Source: http://www.webopedia.com/term/f/fault_tolerance.html

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Network Availability

• RAID – Redundant Array of Inexpensive Disks
• Back-up Concepts
• Manage Single Point of Failure

RAID – Redundant Array of Inexpensive Disks

• Fault tolerance against server crashes
• Secondary – improve system performance
• Striping – caching and distributing on multiple disks
• RAID – employs the technique of striping, which involves partitioning each drive’s storage space into units ranging from a sector (512 bytes) up to several megabytes. The stripes of all disks are interleaved and addressed in order
• Hardware and software implementation

RAID Advisory Board

• Three types
  • Failure Resistant Disk Systems (FRDS) – the only current standard;
  • Failure Tolerant Disk Systems;
  • Disaster Tolerant Disk Systems
• FRDS
  • Provides the ability to reconstruct the contents of a failed disk onto a replacement disk
  • Enables continuous monitoring of these parts and the alerting of their failure
• FRDS+
  • Protect from disk failure – can reconstruct disks by automatically hot swapping while server is running
  • Includes environmental controls
  • FRDS+ adds hazard warning

RAID Levels

RAID 0 – Striping

• Creates one large disk by using multiple disks – striping
• No redundancy
• No fault tolerance (1 fail = all fail)
• Read/write performance is increased

RAID 1 – Mirroring

• Duplicates data on other disks (usually a one to one ratio)
• Expensive (doubles cost of storage)

RAID 2 – Hamming Code Parity

• Multiple disks
• Parity information created using a hamming code
• Can be used in 39 disk array 32 data and 7 recovery
• Not used, replaced by more flexible levels

RAID 3 – Byte Level Parity / RAID 4 – Block Level Parity

• Stripe across multiple drives
• Parity information on a parity drive
• Provides redundancy
• Can effect performance with a single parity drive

RAID 5 – Interleave Parity

• Most popular
• Stripes data and parity information across all drives
• Uses interleave parity
• Reads and writes performed concurrently
• Usually 3-5 drives – if one drive fails, can reconstruct the failed drive by using the information from the other 2

RAID 7 – Single Virtual Disk

• Functions as a single virtual disk
• Usually software over Level 5 hardware
• Enables the drive array to continue to operate if any disk or any path to any disk fails

RAID Summary

• 0 – Striping
• 1 – Mirroring
• 2 – Hamming Code Parity
• 3 – Byte level parity
• 4 – Block level parity
• 5 – Interleave parity
• 7 – Single Virtual Disk

Other Types of Fault Tolerance

Redundant Servers

• Primary Server mirrors to secondary server
• Fail-over or rollover to secondary in the event of a failure
• Server fault tolerance can be warm or hot

Server Cluster

• Group of independent servers managed as a single system
• Load balancing
• Improves performance
• “Server Farm”
• Microsoft Cluster Server