Chapter 15; network management

Whew. Last chapter. What a ride it's been.

Chapter 15 was the shortest since something like chapter 2. It covered some final points of managing a network that don't fall (completely anyway) under accessibility and integrity. The chapter touched on things like documentation, which, while not strictly an integrity thing, will sure help when the printer at IP address 192.168.4.7 stops talking to the printer server at 172.100.38.9.

The chapter also covered baseline measurements, policies, procedures, and regulations, network management software, system and event logs, traffic shaping, and forth.

The real unifying theme amongst all of this material was that it's the tools you need to accomplish the things in chapters 12, 13, and 14. Sudden spike in inbound traffic? Is that a hacker, or were we just slashdotted?

The chapter also covered the day-to-day tasks of network management like updating obsolete hardware and software, scheduled maintenance, and so forth.

A final note: Thanks, Mike. It's been a good class.

Chapter 14: Integrity and Availability

Chapter 14 dealt with the finer points of keeping a network working and useful, or, as the title indicates, maintaining integrity and availability.

Integrity is the soundness of a network - how reliable the OS and hardware are.

Availability is how much "uptime" the network has and how, well, available it is for the user to use.

This chapter covered a lot of very practical, day-to-day stuff. Backups, malware protection, and things like error log checking, redundancy, and so forth were covered, as well as power protection via generators and Uninterruptible Power Supplies, Network Attached Storage, Storage Area Networks, firewalls, RAID systems, and all sorts of other wonderful toys and procedures that make paranoid users like myself all warm and fuzzy inside. If it has to do with preparedness, efficiency, or protection, it's covered either by this chapter or chapter 12. I spent a good chunk of the time reading this feeling incredibly vindicated about a lot of stuff about responsible computing that I've told people over the years.

I loved this chapter, I loved the classroom discussion that followed, and I really look forward to this part of my future career. I like making things work better and keeping them working come what may.

Chapter 13: Troubleshooting network problems

Chapter 13 dealt with what to do when something on a network inevitably goes wrong.

Most systems eventually experience some kind of trouble, and when they do, it's imperative that the trouble be as short-lived as possible. When something does crop up, it's best to identify what the problems and symptoms are (often, this will be obvious) and then move on to a fix. The first step in this direction often takes the form of identifying the affected area, determining what changed to cause the problem in the first place, and then making adjustments of one sort or another (replacing cables, updating or rolling back updates, fixing faulty hardware, reconfiguring something, and so forth) until the problem is solved and then documenting it afterwards.

The chapter also covered various types of troubleshooting tools - various instruments and devices for checking the integrity of a network's cables, the quality of its power flow, and even the traffic emitted by its nodes were discussed. I now want a butt set, a multimeter, and a wireless network testing tool.

An interesting chapter, if for no other reason than I see this kind of stuff as where a lot of the real fun of working with computers comes in. Problem solving is good.

Chapter 12: Network Security

This chapter covered something of a "pet subject" of mine - network security. The fact of the matter is that the modern computing world is analogous to a bad neighborhood and if one isn't careful, horrible fates can befall any network out there.

The weakest link in many networks is often the group of people using it, either the authorized users or outside intruders. Problems can arise from user negligence, policy problems, or deliberate outside attacks. Things as simple as weak passwords or infrequently changed ones can turn into serious security breaches. For example:

Bad Password: "Rover" (The name of the user's dog) - short, a word from a dictionary, and easily discovered through social engineering.
Good Password: 7391-d4V3*ln80 - long, special characters, no recognizable words. In this case, it could be the first 4 digits from the user's library card, a password set on a Wednesday, after the user bought his third Volkswagen and his wife's maiden initials and birth year. If you knew everything about the user and his life, the contents of his wallet, and so forth, you might be able to guess this, but it would be hard.
Excellent password: "xq'@R$JD/W`hn`.*;XvHULwbv+CFP9Y.H<"C$]4lR6(ci/nAhuvU;Yg&Z.rM3S;" - long, random, derived from a random password generator rather than a human mind, uses the full ASCII set, nearly impossible to brute force

There are also risks associated with the equipment itself. Easily-accessed ports or terminals just invite an attack. Wireless signals can be captured and spoofed. Improperly-configured firewalls and routers can be bypassed.

And then there are software risks. TCP/IP wasn't designed with security in mind, so it has several holes. No NOS is completely bulletproof (even the most secure versions of BSD have had one or two successful attacks over the years) and even one improper setting can provide a malicious hacker an entry point.

To combat all of this, good security policies need to be in place. The goal of these policies is to prevent unauthorized access and damage to hardware or software, intentional or unintentional, from happening. Securing data and providing for what to do when an attack inevitably happens should also be on the list of goals for a security policy. Also important is a clear definition of what "confidential" means in an organization.

The chapter also covered encryption, authentication protocols, and wireless network security.

Chapter 11: VOIP

One of the reasons that traditional land-line telephone service is going the way of the dinosaur is cell phones. The other is Voice (or Video) Over Internet Protocol. The advantages of VOIP are obvious - let's say you're in the US and you want to talk to somebody in the UK. Traditional phone service will absolutely kill you for that privilege. VOIP will be free. Other advantages include webcam integration (video phones, in other words) and the ability to more carefully and granularly manage a site's voice and data network.

VOIP can go over traditional analog phone sets via an adapter (in this case, a VOIP router, PBX or even a workstation with an Analog Telephone Adapter) over specialized IP telephones, or over a workstation with a softphone program (like Skype or Ventrillo) installed on it and a headset plugged in.

VOIP can also mean Video Over Internet protocol and in this case encompasses things like the aforementioned videophone, but also live camera feeds (a lot of modern security systems use this) or streaming video from a server (such as youtube).

Behind the scenes VOIP uses a protocol called SIP (Session Initiation Protocol) to regulate the packets and make sure the incoming data is formatted in a manner the player it's going to can make sense of.

This one is near and dear to me - I use Skype to stay in touch with some friends who are out of state, and I watch online TV on hulu and movies via Netflix.

Chapter 10: TCP/IP Arcana (In depth TCP/IP)

This chapter covered three primary topics: subnetting, mail services, and TCP/IP utilities.

Subnetting is the process by were a single IP address can be split into more sub-nets. This is great (for example) for large networks that use a significant potion of their private IP space. It's also good for added security, improved performance, and simplified troubleshooting. Subnetting is a achieved through a process which ANDs the binary value of an IP address with another block of 4 octets called the subnet mask to provide a subnet address.

TCP/IP mail services are what one would expect – email. However, it's not quite that cut and dried. SMTP (Simple Mail Transfer Protocol) is the protocol for moving email around, among other things, the Internet. It operates over port 25 and uses a format called MIME (Multipurpose Internet Mail Extensions). MIME was released by the IEEE in 1992 to make email more versatile. Before MIME you couldn't for example, include pictures in an email. (You couldn't include malware, either, but hey, you have to take the bad with the good.) There's also POP (Post Office Protocol) which operates over port 110. Also out there is IMAP (Internet message Access Protocol) which was developed as a more sophisticated option over P POP3. It can replace POP3 without changing programs.

The final portion of the chapter covered utilities like traceroute, host, dig, and netstat that are used for setting up and troubleshooting a network.

Reading this chapter, it finally started to sink in why it's possible to make a living doing this stuff – to a layperson, a lot of this must be dauntingly arcane.

Chapter 9: Network operating Systems

This chapter dealt with NOSs. Network Operating Systems aren't that different at their core than a workstation OS – they're a framework that allows a collection of useful programs to be run and also a way of coordinating the transfer of resources around a network. A server can be configured to divide users into groups with different sets of privileges and access to different programs and batches of data, they can function as “super-routers” that can direct network traffic in sophisticated ways, and they can also provide monitoring, reporting, security services, and the like.

While other ones are out there, there are 3 primary flavors of NOS: Windows, UNIX, and Linux. Windows is the entry of Microsoft in this arena, and is probably the most user-friendly of the three. It's equipped with a very nice, intuitive GUI. UNIX is available in both commercial and open-source varieties and has been around in one form or another almost as long as computers have. Linux is an open-source OS that started as an alternative to UNIX but has since branched and grown into its own product. All three are in heavy use in the modern world.

My strongest reaction to this chapter was a strong desire to install and play around with a NOS. I'm hoping to get the chance soon – I'd like to make my home network a bit more sophisticated.

Chapter 8: Wireless networking

Chapter 8 covered the various aspects of wireless networking. The chapter led off with a summary of the various frequencies used by wireless networks and spent some time discussing the various things that can cause trouble with wireless signals (anything but air, basically) and from there moved into WLAN architecture. Since WLANs don't have actual cables, their topologies are different than wired networks. It seems to primarily boil down to a P2P style ad hoc configuration or a star-like access point setup, though.

The chapter also spent some time on the IEEE 802.11b, 802.11a, 802.11g and the recently-released 802.11n standards, which govern most wireless networks in use today, and Bluetooth, which covers a sizeable chunk of the remaining ones.

The chapter also covered setting up a WLAN and also went into some detail on satellite data transmission.

Honestly, whenever I see "wireless," I cringe a little bit. It's less secure and less efficient than running cables, and I'm not a huge mobile device user. Still, it's good to know - it's just not my favorite topic.

Chapter 7: WANs and remote connectivity

Chapter 7 covered WANs, or Wide Area Networks. A WAN is a network that spans more than one site. My current employer has a WAN running some proprietary software that spans all of the stores in the company that we use for internal communication and day-to-day operations. WANs have their own topologies, in this case based on sites rather than nodes. Bus, ring, and star are present just like in LANs, and they mean roughly the same thing. A bus is a network where each site is connected to no more than two other sites in a line, a ring is similar to a bus, but the “ends” meet, and a star configuration has a central site to which the others connect. There are also mesh topologies (all the sites are directly connected to each other – high performance and fail safe, but very expensive) and a tiered topology (basically connect several star networks in bus configuration – the central sites basically function as the network's backbone).

The chapter covered the use of PSTN (Public Switched Telephone Network) or, more humorously and appropriately POTS (Plain Old Telephone Service) and its utility in data transmission. As it turns out, there are a number of different ways to get data over phone lines. You've got old, slow, crummy, sad dial-up service, which is about as useful in today's age as a handcart is for moving a battleship. (Then again, it's still better than carrying the battleship by hand...) There's ISDN which is slow and expensive (and not very common, either). There's DSL which is actually pretty nice if you get a high-throughput plan. And then there are T-lines, which used to be the fastest available, but are now getting serious competition from DSL. If you're able to read these words, you know speed is good where data transmission is concerned.

The chapter also covered SONET, a high-speed dual-ring network setup (one going clockwise, the other counterclockwise) over fiber-optic cable. It's exceedingly fault-tolerant and it's also very expensive. The most interesting thing about SONET to me, though, is that there's still a viable use for a ring-topology network in today's world.

Finally, the chapter covered remote access, touching on dial-up networking, remote access servers, and VPNs. The application of these technologies in the real world is obvious – most business travelers now own laptops for the express purpose of being able to access data back at their home office. VPNs also have the additional handy feature of allowing greater security at a public hotspot if used to connect to a more secure system.

I got a kick out of this chapter – I just think it's cool that the old ring topology is still useful in today's world, and reading about the different types of WAN technology was a fun walk down memory lane.

Chapter 6: Network Hardware

Chapter 6 dealt with the hardware side of things in detail. The first thing the chapter covered was various types of NIC (Network interface Card). NICs come in a dizzying array of different types, and are available for just about every sort of expansion connector known to computing (PCI, PCIe, FireWire, USB, CardBus and ExpressCard for laptops, and built-in ones integrated into the motherboard of a computer) Regardless of how you connect them or what kind of cable (or radio signal) they use, however, a NIC is fundamentally a NIC. They're used to convert data into electrical impulses, light, or radio waves for transmission to the next NIC and for converting those same impulses, light beams, or radio waves back into data when it arrives.

The chapter also covered repeaters, hubs, switches, bridges, and routers. These devices, collectively, form much of the backbone of a network, and perform functions analogous to stoplights and street signs in a city, managing where traffic flows, what gets priority, and that everything (or at least as much as possible) gets there intact. Repeaters and hubs are the simplest, just rebroadcasting whatever comes into them. The biggest difference is that a repeater only broadcasts out to one output, whereas a hub will have several. Hubs have largely become a thing of the past – switches these days are so cheap that you'd be silly not to use one. Switches and bridges connect segments of a network to each other and operate by actually sending packets just to their destination IP rather than just broadcasting them like a hub. Small wonder they're more efficient. Bridges are basically two-port switches, used to connect just two segments together. Routers are like switches on steroids. They have an array of filtering, reporting, and security features built in. They are more than one needs sometimes, but they're great for setting up intra-nets that still connect to the Internet, because they can route traffic from an entire network out to the Internet via a single public IP.

The chapter was useful, but seemed a touch overlong for the material it covered – these connectivity devices are vital but somewhat self-explanatory. Then again, maybe it's just prior knowledge talking.

Chapter 5: Network Topologies

Chapter 5: Network Topologies

This chapter dealt with the physical layout of networks, and when you boil it down, there aren't many of those. The three basic types of network are bus (computers set up in-line, passing data down the line bucket-brigade style), ring (like a bus, but the ends are linked, so data won't always have to travel so far) and star (all of the nodes are connected to a central device of some sort, which coordinates traffic out to the individual nodes). Of the three, star is by far the most common in the modern world, which makes sense. A star network is a typical client/server network, and is also the most efficient type of network, especially considering the power of modern computers.

You still see the other types, though. Connecting an ipod to a computer temporarily creates a small bus-style network, and ISPs often use a high-speed double ring network called SONET. You'll also see what are called hybrid networks, which most commonly result from connecting two networks of different types together.

The chapter also covered what's known as a network backbone, which is another way of describing all the connectivity devices on a network. Things like hubs, switches, and routers form a network's backbone, though a more accurate term might have been “spinal cord.” They function in much the same way as a spinal cord does, passing data around the network and allowing one node to communicate with another efficiently. Also much like a spinal cod, they don't generate any information themselves most of the time; rather they just insure that existing data gets where it needs to.

The chapter also covered various types of Ethernet standards (my word we've come a long way in a short time...) and useful technologies such as Power Over Ethernet, which a friend of mine who works IT for a large medical company swears by. Apparently, PoE is great for powering touch screen terminals in medical labs.

An interesting chapter, overall. In particular, it was neat to find out about some of the ways networks have grow and changed over the years. We've come a LONG way from the old token ring networks.

Chapter 4: TCP/IP

Note: I give. Trying to make this a "real blog" with NaNoWriMo, a second class, and the busiest time of year at work (I work in retail - one of the reasons for taking this class in the first place - so I can get into a career field that's more cerebral and more lucrative) pressing down on me is proving to be a bit too much. Until I get caught up, these blog posts are going to be much shorter and less in-depth than the previous ones. If I get a chance, I may go back and crank them up to a higher level, but for now, I just need to complete the assignments.

TCP/IP is the suite of protocols that most modern networks (including the internet) run on. However, despite the name, it's more than just TCP and IP - the suite also includes protocols like UDP (useful in applications like VOIP) and the ARP/RARP protocols used for address resolution. Basically, TCP/IP is the language that allows a network to communicate. TCP and UDP to move data around, ARP and RARP to establish addressing, ICMP to report any problems with the path the packets are taking, and so forth.

The chapter also covered addressing. The web currently runs on IPv4 (an IPv4 address looks like this: 192.168.24.130) this is all well and good, but the addresses are getting used up at a rapid pace. One solution to this is IPv6, which has a lot more available address space (79,228,162,514,264,337,593,543,950,336 unique addresses as opposed to IPv4's approximately 4.3 billion, to be precise). One stopgap measure that's been used is private network IPs, which means that you can re-use a block of IPs as long as they're not connected to the larger internet. My router at home, for example, uses the 192.168.x.x IP space. So does everybody else who uses that type of router's network. The router itself, however, uses a public IP issues by my internet service provider.

The chapter also covered DNS or Domain Name Service, which is nothing more, and nothing less, than the process which turns www.mchenry.edu into the IP address that will direct my web browser to the college's web page.

An interesting chapter from a theoretical point of view. I was dimly aware of TCP/IP, DNS and the like when I started reading (thanks largely to the early episodes of Security Now) but this got a lot more in depth.

The Hard Stuff: Cables and other Transmission Media

That's right, everybody! This week it's hardcore, hard-wired hardware!*

So you've got a bunch of computers to network and they're ready to go. How do you go about actually connecting them? You've got three options:

1. You don't physically connect them, relying on a wireless signal. This can be convenient, but you're using radio waves. And, well:

   "Radio is bad. I mean, it's necessary. I'm not saying we don't all use it. I do. I've got WiFi here. I've got it wrapped up in a WPA encryption with a passphrase from hell that I got from GRC.com/passwords. So I'm as secure as I can be. But several times during the history of this podcast we've talked about vulnerabilities in, for example, Intel's WiFi drivers. There was one not even that long ago where it was found that down in the actual packet processing, way down at the bottom, the first place the packets go when it comes hot in off the aerial, off the radio antenna, had an overflow. So before encryption and decryption, before authentication, before anything else, it was possible to simply broadcast a malformed, deliberately malicious bit of radio noise and take over a machine." - Steve Gibson (Security Now Episode 158)

   (There will be more about wireless networking in 5 posts.)
2. You use cables of some kind to connect your devices. This is more secure and often more reliable, sometimes cheaper, and often a higher-performance option than wireless.
3. You give up and kick it old school.

For the purposes of this blog post, we're going to assume that option 3 is not an option, and, realistically, in today's marvelously high-tech world, it's really not.

Unlike my two blog posts previous, I'm going to diverge a bit from the order the book uses and talk about cables first, because in my humble opinion, it makes more sense to do it that way.

There are two main types of cable:

• Copper Wire: This can be anything from Coaxial cable, (yep, the exact same stuff you get cable TV through) Unshielded Twisted Pair, (which is some of the most evil stuff on the planet, but more on that later) and Shielded Twisted Pair. These all have their sub-types, but those are the basics.
• Fiber Optic: The "good stuff" as it were, fiber optic cable sends data as light rather than electricity. As you would expect, fiber optic cable is very fast, but it's also expensive.

These cables carry data in one of two ways: analog or digital.

• Analog Data: Analog data is kind expressed as a wave. The human voice is an analog signal, and if you compare it to one of those horrific automated talking phone systems, you'll immediately grasp one of the major benefits of analog - it's able to carry a lot more data than digital over a similar medium. However, it's extremely vulnerable to noise. Noise is anything that interferes with the signal in this case. For a perfect example of noise, just put something on the radio and drive past a hospital. When the signal cuts out and is replaced by static, you are experiencing noise.

• Digital Data: Digital data is sent as a series of pulses. It has the advantage of being more noise resistant, because either there's light/voltage or there isn't.And there you have it; the basics of the physical parts of a network.

And there you have it. The hardware end of network connections.

*Apologies to Steve Jackson Games

The Standards of Networking and the OSI Model

Welcome back! This time around, we're going to deal with two topics; Networking Standards organizations and the Open Systems Interconnection (OSI) model. This post is likely going to be quite vocabulary-heavy.

Networking Standards Organizations

Like just about everything else, networking has its own set of standards. On a base level, this means that the industry has agreed on a set of dimensions, pin locations, etc. that will apply universally for similar equipment across the entire industry. Or, to put it another way, it's the same principle in play that allows you to plug your blender and your television into the same type of electrical outlet.

An important note: where performance is concerned: standards refer to the minimum performance that is acceptable for a given thing. Going above this is often desirable. Those of you who read this and are familiar withPC gaming need look no further than this: while a mid-range Dell from a year back will run high-end games like Crysis, it won't do so nearly as well as a custom-built gaming rig. (Or a pre-assembled gaming PC from a high-end company like Falcoln Northwest.) In gaming, it's almost always a good idea to exceed the minimum system requirements by as much as is practical. The same goes for network components. Just like a Core i7 or Phenom II is a better choice than an athlon or centrino, so often is a higher-grade cable a better choice than a cheap one.

Unlike a lot of industries, the computer industry has been around for a comparatively short time, even when compared to other newer technologies like television. Because of this, there's no one central governing authority over network standards. In my personal opinion, this is actually a good thing. The various organizations are able to specialize, which (at least, it seems to me) offers better results overall.

Some of the Major Players:

ANSI: ANSI (American National Standards Institute) is the proverbial "big boy" on the block - it's an organization composed of over a thousand industry and government types, and they determine far more than just computer standards. Unlike many governmental and pseudogovernmental organizations out there, they enforce their standards through voluntary compliance rather than through more heavy-handed measures. They have their fingers in a lot of pies - this organization is extremely influential, and getting ANSI's stamp of approval on something is rightly viewed as a favorable thing due to their rigorous testing.

EIA and TIA: The Electronic Industries Alliance and Telecommunications Industry Alliance, respectively. The EIA is a trade organization that draws its membership from US electronics manufacturing firms. The TIA is a spun-off branch of the EIA that then merged with the United States Telecommunications Suppliers Association (hereafter referred to in the mercifully-shorter form of USTSA). THe EIA helps ANSI set standards, the TIA regulates what its name would lead you to believe it does - basically anything AT&T has its hands in (phone, wireless, satellite, fiber optics, the Death Star*)

*Okay, not really the Death Star.

IEEE: Not just a phoenetic spelling of a high-pitched scream, the IEEE (Institute of Electrical and Electronic Engineers) is the first international organization on our list. (They are often referred to as "I-triple-E.") The goal of this organization is to promote, in a nutshell, the advancement of all things Information Technology. They host a lot of symposiums, conferences and the like, and they also publish papers on various technology topics. This is a highly-respected and, frankly, very cool organization. If you're only going to click on one link in this post, make it the one attached to this paragraph.

As I was looking up the various sites for this paragraph, I actually got somewhat distracted on the IEEE's page, and followed a link to one project of theirs that I thought was particularly interesting: http://www.trynano.org/.

ISO: The International Organization for Standardization is headquartered on famously-neutral ground in Geneva, Switzerland. Its membership is drawn from a staggering 157 countries, and its goal is to foster global exchange of information and free trade through technological standards, which makes them almost as cool as the IEEE in my book. Like ANSI, they aren't limited to

computers, but have influence over a wide range of different spheres including a lot of the technologies used to bring things to market (shipbuilding, packaging, etc.) and banking.

ISO's name isn't a scrambled acronym, but rather the Greek word for "equal," the use of which is meant to convey their dedication to standards.

ITU: The International Telecommunications Union is a UN agency that regulates international telecommunications. These are the people who regulate things like radio frequencies. Founded in Paris in 1865 and since relocated to Geneva, Switzerland, they're more focused on issues than standards, but they are deeply involved in global internet implementation.

ISOC: ISOC is the shortened form of Internet Society. They're a relatively new organization (founded in 1992 -unsurprising given the relative youth of IT) and they concern themselves with technical standards for the Internet. Subgroups include the IAB (Internet Advisory Board) and IETF (Internet Engineering Task Force). Interestingly, the IETF is wide open - anyone can submit astandard for approval.

IANA and ICANN: There's a lot in the textbook about these two, but it boils down to this: these are the central authority for IP and domain name addressing. (Yeah, just a little bit important!)

The OSI Model

The OSI model was created by ISO, the International Organization for standards. (Anyone else think they named it that just so they could have a full set of the ways you can arrange I, S, and O?) The acronym stands for Open Systems Interconnection and is used to describe how various parts of a network interrelate. It's admittedly a little vague as to what goes in which layer at times, but it's still a useful abstraction. As the previous sentence infers, the OSI model is based on a set of layers, seven, in fact. Those layers are, from highest to lowest:

Quick vocabulary note: Where computers are concerned, "lower"

7. Application: One quick piece of disambiguation: This doesn't mean the program that sent the packet. (So, for example, this doesn't mean Skype or Outlook or your BitTorrent client.) The application layer is there to allow those other programs a means by which to communicate with the lower levels of the network. An example of this layer in action: a user punches a URL into their browser and hits Enter. The browser's API hands the request off to HTTP. HTTP then sens the request on from there. This process and the HTTP protocol live up in the application layer. (Along with other protocols like DNS and FTP)

6. Presentation: Presentation layer protocols function as translators. Translation layer protocols are what translate a stack of ones and zeros into something humans can interact with. When you

need an MP3 turned into music or a blob of encrypted data turned back into something intelligible, it's going to happen on the Presentation layer.

5. Session: Session layer protocols are used as a kind of maintenance system that manages connections between multiple nodes. They detect interruptions in service between the two nodes and synchronize communication. While not as sexy as the stuff up in the presentation or application layers, they're important because they can help you figure out when something has gone amiss. An example: you're downloading something. Something big. If not for session protocols, if you lost the connection, you might not know it for much much later.

4. Transport: The data-transfer protocols like TCP and UDP that do the actual heavy lifting of file transfer live in this layer. These protocols can vary a bit. Some just push data through without verifying whether it gets there or not (UDP) others, like TCP, establish a three-way "handshake" of acknowledgements from both ends to ensure every last bit of data gets there, re-sending bits that get lost.

If you're wondering what you would use UDP for after this (like I was when I first heard about it) look no further than VOIP. A lost packet in VOIP will just cause a little blip or bit of random noise not unlike static on a VOIP connection. For something more critical like transferring a large file, though, it would be pretty risky to use an unverified protocol. For a much better description than I'm capable of giving, I direct you to Security Now, Episodes 25 and 26. Steve Gibson does an absolutely fantastic job of explaining the underpinnings of the internet. (Also: if you're reading this and aren't already listening to that excellent podcast, download an episode for your next long drive. It'll hook you.)

3. Network Layer: Routing takes place on this layer. Data that's been passed down through the Application, Presentation, Session, and Transport layers becomes packets here and a route from its origin to its destination is determined. This is a fairly intelligent process that accounts not only for where the packet needs to go, but how high-priority it is and how much congestion is being caused by other traffic that is already on the network. The protocol that you've probably heard of that

operates on this level is IP (Internet Protocol - one guess as to where that's used).

Segmentation and Fragmentation: both of these processes are used to pare big hunks of data down into smaller ones. It's usually better to segment data on the Transport layer, but if that's not viable for some reason and the data is still in pieces too large for a network to handle, fragmentation occurs down on the Network layer.

2. Data Link Layer: Really two sub-layers, the Logical Link Control or LLC and Media Access Control (MAC), the Data Link Layers does error checking and flow control, and preps data to flow through the Physical layer.

1. Physical Layer: Here's where the data gets transformed for transmission. What it's transformed into depends on what it's being sent through. If it's going through a copper wire, it'll be voltage. If it's going through fiber-optics, it'll be light, and if it's going over the air, it'll be radio waves. At the destination, the other node picks up the signal and repeats the process through the layers in reverse.

[This post composed in Google Chrome running on Windows 7]

The Basics of Networking

Most (possibly all) of the posts in this blog will be a paraphrasing of one of the chapters in my textbook. I'm going to go into a bit more depth than is strictly required for the class, and I'm also going to try to make this as entertaining and accessible as possible, so even if you aren't my instructor or one of my classmates, you'll hopefully get something out of reading this. I have another ulterior motive, too. I figure if I make this interesting to read, it'll make it better as a study aid for me when the time to study for the Network+ exam rolls around. This one's going to be pretty long and dense because I'm defining a lot of terms.

The Benefits of Networks

On a base level, any time two electronic devices are connected to each other so they can communicate, you have a network. Many people in the modern world have built simple networks without even realizing it - the act of connecting an MP3 player to a computer so one can transfer music files over is a basic and user-friendly form of networking. The advantages of networking are apparent in that same example; being able to share data across the network allows you to achieve a result easily with the two devices combined that would, at the minimum, be substantially more difficult than if they weren't connected. The computer can connect to the internet to download music quickly and store a huge amount of it on its internal hard drives (especially in today's world of the $80 1TB HDD). The MP3 player, if it can access the internet at all, is probably slower and almost certainly has less storage space than the PC, but it's small enough to take with on a jog or in the car with a minimum of hassle.

Other benefits of networking (beyond portable music) include the diminished need for devices in a business setting. If everybody can use one printer, one internet connection, and one centralized server or NAS, it cuts down dramatically on the cost in time, space, and money of setting up a digital office and allows for easier collaboration, too. Need to send the spreadsheet file down to Tom in accounting? No problem. Just send it to his computer via the network rather than putting it on a disk and walking it down to him like they did in the old days.

Networking also makes wondrous things like SaaS available, a good example being Google Docs. Which allows a group of collaborators spread all over the world to use the same program to edit the same files without ever meeting face-to-face.

The Flavors of Networking

Networks come in a variety of flavors, but the most common types are peer-to-peer and client/server.

Peer to Peer networking: Peer-to-peer (abbreviated P2P) networks are links of direct communication between two or more computers. No computer exercises any sort of authority over the other(s) and no computer screens any traffic as it passes between two computers on the network. Peer-to-peer has something of a shady reputation from the old days of Napster, Kazaa, and the like, and it continues today as bazillions of people use P2P BitTorrent connections to pirate movies, music, and computer software at a rate that would bring a tear to Edward Teach's eye. However, P2P utility doesn't stop there - if you've ever used Skype to talk to someone over the internet, you've used a P2P network. Walkie-talkies are a simple P2P network. P2P networks are simple to configure and cheap, but they suffer from inflexibility, potential insecurity, impracticality once they get large, and of course, their shady reputation. Yarr.

Client/Server Networks: This is where the real fun starts. Client/Server networks rely on a central computer (called a sever) to route traffic around the network to other computers called (three guesses...) Clients. Clients are usually personal computer. In an office environment, they're typically called workstations. Another way to think of how traffic moves around a client/server network is the post office or a shipping company. Instead of directly moving the mail from its origination point to its endpoint, it goes to a hub of some sort first and is then sorted and sent on its way from there. This is inefficient if you, say, want to send something to your neighbor (that's a better use for a P2P type connection) but what if you want to send a bunch of packages (like Christmas cards, for example) to a bunch of people? Suddenly the P2P model is a lot less efficient.

Servers: Typically servers are fairly powerful (and often expensive) computers. Modern servers often have several fast multi-core processors, a large amount of storage, etc. Prices for them in the tens of thousands of dollars are not uncommon at all.

Clients: Client computers are typically "normal" computers. They typically only cost tens of thousands of dollars when their owner is a rabid gamer.

Client/Server networks also have the advantage of being potentially much more secure. Servers can impose access limits, various forms of authentication, and other controls on traffic moving throughout the network. This type of network also makes things like printer sharing a workable reality. Their biggest downside is that they can get complex pretty quickly.

LAN, MAN, WAN
And maybe the loss of some SAN

LAN, MAN, and WAN are terms used primarily to describe the size and scope of a network.

LAN: A LAN, or Local Area Network, is a network typically confined to a single building. That doesn't, however, mean that it's small. The single server and 18 workstations (13 cash registers, 4 search terminals, and 1 receiving computer, plus 7 handheld mini-computers used for inventory) that I have at my current workplace is a lot smaller than the network used at the MCC (the college I attend) but both are LANs because they're both confined to a single building. (MCC says that it's multiple buildings for organizational purposes, but you can walk through them all without ever stepping outside, so screw it, it's a LAN.)

MAN: A network that extends beyond the boundaries of a building (again, no matter how huge - even the Pentagon is still just one building!) becomes a MAN, and no that doesn't mean it's undergone some rite of passage or that it's somehow a male network now - MAN stands for Metropolitan Area Network. An example of a MAN is a modern military base (particularly an Air Force one) with a large number of computers spread around various building all part of the same network.

WAN: The 800lb gorilla of networks, WAN stands for Wide Area Network. Wans cover even bigger areas than MANs. If you have a computer in Miami communicating with a computer in Anchorage (or even one in Atlanta) congratulations, you have a WAN. The internet can be seen as a humongous WAN.

Other "ANs"

CAN: Campus Area Network
GAN: Global Area Network
PAN: Personal Area Network (in this case not actually a network at all - just a wire management system, but can also refer to things like a bluetooth headset and cell phone)

"Okay, So How Do You Build One?"

Networks do not just spring up out of the proverbial earth. Like any other complex device, they need to be assembled. Here's a list of some of the more common components you'll see when building a network:

Hardware and Software

• Client: A computer (or sometimes the person behind it) that asks for data, access, or other resources from a...
• Server: A computer at the center of the network that manages the resources the client asks for.
  
• NIC: Network Interface Card. This is where you plug the cables that connect computers to each other on a wired network in. Most modern PCs come with at least one standard on the motherboard.
• NOS: Network Operating System. A server OS optimized for, well, server tasks. It's great at routing data around the network, but probably wouldn't be your first choice for, say, computer games.
• Node: Something on the network with a unique address. The Server is a node. So is each workstation. So, for that matter, is that crummy old printer that's destined for a beatdown in the parking lot someday.
• Connecitivity Device: A device used to connect multiple networks or multiple parts of a network to each other. The DSL modem/router your home ISP gave you would fall into this category. Companies like Linksys and D-Link make a lot of their money selling consumer Connectivity Devices.
• Transmission Media: The wires or radio waves used to actually transmit packets around a network.
  

General Concepts:

• Segment: If the network is a city, a Segment is a neighborhood wrapped around a cul-de-sac. It's a bunch of devices (nodes) that use the same communication channel for their traffic.
• Backbone: The part of the network that does all the traffic management. Usually made up of Servers and Connectivity devices.
• Topology: The actual, physical shape the network takes (or at least the one it takes if you draw a diagram). A P2P network would look like a so-called "ring" or "bus" layout, with a bunch of computers all connected in a line (bus) or, well, ring. A Client/Server network will have more of a "star" configuration, with connections radiating out from a central point.
• Protocol: A standard method or format that is used for communication between the nodes on a network. Protocols are important, because without them, you'd never get reliable data transfer. Data is broken into packets before being sent, and if these get jumbled, you might as well have pseudo-random "noise" at the end for all the good it'll do you.
• Packets: Basically bite-sized chunks of larger blobs of data. Big files are chopped into packets before transmission.
  

To picture how data transfer with packets over a network goes, just imagine getting a bicycle shipped to you via UPS or a similar carrier. Instead of putting the bike pre-assembled in a HUGE box and sending that, the manufacturer will probably break it down into three: you'll get a round box with the wheels, the frame with a label on it, and a box with all the smaller parts (tires, chain, gear shifter, etc.) in it. When the packages arrive, they'll say something like 1 of 3, 2 of 3, and 3 of 3 and you'll have to assemble them from there. Packets work kind of like that.

• Addressing: Remember those unique addresses all the nodes have? This is the system used to assign them. A common and widely-used type of address that a node might have is an IP (Internet Protocol) address. Those are what's used on the Internet to route traffic.

"So What do I do With it?"

So we've established how networks go together and their component pieces, and even what the benefits of them are, but not the Why to go with the What and How. Here are some common uses of networks:

• Communication: I mentioned Skype back under P2P networks, but there's also Vonage, Ventrillo, and other VOIP (Voice Over Internet Protocol) services out there, to say nothing of Instant Messenger clients, email, forums, newsgroups, Blogs, and (God help us) even Twitter. Oh, and that cell phone you've got? It's part of a network, too.
• File Sharing: You're on the first floor. Your boss, on the eleventy-third floor needs that document now. The elevator is running slow as usual. And you don't want to run up eleventy-two flights of stairs. Send it to him through the network. Not only have you saved yourself the time of actually walking there, you don't have to take the time to write the file to a disk, CD, or USB drive, either.
  
• Printer Sharing: So there's thirty of you in the office. You tell me what's a better use of the money - a cheap, crummy printer on every desk that gets in the way anyhow or a halfway decent one that you all share and better coffee in the office? Especially since none of you print much anyhow. Similar principles apply to sharing of other resources, too. (For example, scientific instruments)
  
• Cloud Computing: This is getting more popular these days. I already mentioned Google Apps, but things like Amazon's S3 would also apply, here.
• Gaming: Ever been to a LAN party? They're fun. A bunch of people supply their own computers, create a temporary LAN, and play some sort of multi-player game. Good clean fun.
• Secure Access: If you've got important data that needs to be seen by only certain eyes, a properly bolted-down network can make being sure that those eyes and ONLY those eyes see it much, much easier than doing the old routine where you handcuff a case to some guy's arm.
• Management Services: Or, keeping the IT department from going hair-pulling bald. Networks offer a lot of flexibility and functionality for managing the individual nodes hooked up to them. It's possible to do things like tracking software usage, software-level system maintenance, etc. from a server on a network rather than walking around and sing each workstation separately. One can also monitor and regulate user behavior from a central location.
  

So there it is: the basics of computer networking. From here on is, it gets a lot more specific.

[This post written in Mozilla Firefox 3.5 under Windows XP]