How to Fix Three of the Most Common System Problems Without Restoring a Backup

Corrupt system files, account lockouts, and accidentally deleted data are three scary computer problems that often send people running for their backup drives. While restoring a backup may technically fix things, a full system backup is usually a very time-consuming overkill in these cases, and nobody likes the time-warp effect of restoring one (e.g., if your last full backup ran a week ago). When these problems occur, fixing them can be far simpler than you might think.

Problem 1: Corrupted System Files - Unable to Load the Operating System

A sudden power outage or system crash can corrupt files that are part of your operating system's essential guts. When these things happen, people who have backups tend to just jump straight to them, but then we're at the time warp problem—if you've already done a week's worth of work since the last backup, that data is lost. Instead, you should first attempt to repair or restore just the system files.

Both Windows and Mac OS X have these capabilities either built in, or on their install discs. Good preparedness doesn't just mean making backups, but also making sure these discs are safe—they can save you some major heartache.

Solution:

 

Windows: Corrupt system files happen a bit more frequently in Windows, but it's not difficult to fix most of the time. You should make use of Windows' built-in System Restore, which basically makes daily, miniature backups of your system. It doesn't touch your data—it just backs up system files, so it's absolutely perfect for these sorts of problems. If you're able to boot your PC into Safe Mode (pressing F8 while booting up should do the trick), you can find System Restore in the System Properties settings. If your PC won't boot all the way into Safe Mode, then you'll need your Windows install disc. Booting into that disc will give you the option to use System Restore right on the spot. Since it runs on a daily basis, you can even choose how recent of a snapshot you want (just in case you think the problem started a couple of days before everything stopped working).

Mac: For Mac, it's pretty common that, instead of corrupted files, that you might have broken permissions or other file system issues. You can correct a lot of these sorts of issues by rebooting into Safe Mode (reboot the computer while holding down the Shift key). Booting into Safe Mode will force checking and error correction on the file system, delete cached files, and start the computer in a limited working state that doesn't include anything but the basics. Once fully booted into Safe Mode, you can reboot the computer normally again, and hope that the problem was taken care of in that automated process.

 

If it wasn't fixed by that, you can use your OS X install disc to run Disk Utility and try to repair the disk. Don't worry, it's automatic, too. Boot into the install disc by inserting it into the drive, and rebooting the computer while holding down the C key (once it starts booting the installation disc you can let go of the key). After it loads and has you choose a language, click on the Installer menu at the top of the screen, and select Disk Utility. Inside Disk Utility, choose the tab for First Aid, find your hard disk in the sidebar and expand it to see the partitions, then select yours (usually named something like "Macintosh HD"). Click the Repair button, and then wait patiently for it to finish. If all goes well, it should give a pleasant report that the disk has been repaired. If, instead, you get a notice about corrupted files, then you can take the final step and restore your system.

Restoring all system files in OS X is actually pretty simple, because you just reinstall the OS. Assuming everything goes alright during the installation (basically, as long as the hard drive's healthy), this will only replace the system files, leaving your personal files untouched and as you left them.

Problem 2: You Can't Log In - Either You Forgot Your Password, or it Got Changed on You

If it's just an issue of a forgotten password that's left you unable to log in (or an unfunny prank by someone who knows what it is), you can reset it pretty easily (and get back to work without hassling with restoring a backup):

Solution:

Windows: For Windows users, you need to take action prior to losing access to the account (which means you should do it right now). Go to your Control Panel and select "User Accounts and Family Safety," then click on User Accounts. There you'll find the option to create a Password Reset Disk—just follow the instructions and keep it somewhere safe. If you lose access to your account, you can use this to get back in with a brand new password.

Mac: For Mac OS X, boot into the install disc and choose your language, then choose "Reset Password" from the Utilities menu. If that sounds too easy, it's because it probably is—any OS X install disc for the same version installed on the computer will work.

 

If something more mysterious is going on with your user account, you need a way to get back into your system to try grabbing some of your more recent files, and to investigate what caused the issue. As a safety net, you can keep a separate administrator account on the system, just so you can get back in and check things out. If something malicious caused the lockout, your secondary account should be able to delete the offending files. If not, Windows users can use System Restore, and Mac users can drop in a fresh OS X system install.

Problem 3: Lost Data - Or when You Accidentally Delete Your Life's Work

If you accidentally delete a large chunk of your data—but not anything that affects the OS itself—then a full system restore is definitely an option, but it should be the last one you turn to.

Solution:

Partial Restore From Backup: If you've taken the time to ensure that your backups are accessible, specifically for instances like this, you can simply grab the now lost data from the most recent backup you made. If your backups are compressed into enormous archives, then they're not exactly quick or easy to work with in a case like this. Making full backups that are basically mirrored copies of your hard drive is far more useful, since you can use them for any amount of restoring that may be needed.

Use a Rescue CD: A rescue CD, like Disk Drill for Mac or previously mentioned Recuva for Windows, can scan your drive for deleted files and restore them if possible. It's usually not a problem if it hasn't been very long since they were deleted.

Save Redundantly: Using a rescue CD has a decent chance of working, but it's easier to preemptively cover the possibly of accidental deletions by saving important files to two different locations (preferably on two different hard drives), or by keeping a daily backup of your most important data. It's not practical in any way to back up your entire system every day, but it's not too much of a hassle to back up a few critical files—like your My Documents folder. If your daily work is seriously important, it'd be best to practice both methods, and invest in a small external hard drive since it can hold both your small daily backups, and also serve as the space to use for double-saving important files.

 

Cloud Storage: This is when it's also a good idea to have a backup plan for your backup plan. Use cloud storage services like the beloved Dropbox for important files, use a service like Flickr or Picasa Web Albums for your photos (or even store them as regular files in a service like SugarSync). Amazon Cloud Drive even allows you to store 5GB worth of music files without buying anything. You don't have to pay a thing if you use multiple free plans and spread your data across them.

By Matthew Rogers

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How To Fix Common Mac OS X Problems Without Rebooting

There's lots of common OS X problems and situations that can be overcome with out a single reboot required. Here's how.

 

There are those who simply never shut down — people who are so adverse to rebooting their machines they do everything in their power to avoid it. But energy concerns aside, there are tons of valid reasons for doing so. Some prefer a persistent workspace, while others might run home servers. For these people, continuous uptime is an must. But driver updates or stubborn apps are all it takes to bring your system to a reboot-worthy halt.

License to Kill Tasks 

OS X is a relatively stable operating system, but isn't without its faults. On occasion, the Dock may freeze, or your menubar might crash — and there's simply no way to force close these processes like normal apps. Terminal, however, makes it easy to regain control.

Dock or virtual desktop type...  

killall -KILL Dock
    

If the menubar disappears or stops responding...  

killall -KILL SystemUIServer

And finally, to force close Finder (should the usual GUI approach fail)...

 killall -KILL Finder

  
Depending on how your Mac is setup, you may require administrator privileges. If that's the case, simply include "sudo" before each of the above commands, and type in your password when asked. 

Force Close Unruly Apps  

Command + Option + Escape. However, it only applies to those applications that run from the Dock, excluding the likes of Dropbox or Last.FM that choose to live in the menubar instead. Should any of your background apps freeze, you'll need to take a different approach to shut them down.

Activity Monitor is found in your Utilities folder, and lists all of your Mac's currently running processes — including those missing from the force close GUI. From here, it's a simpler matter of identifying problem processes and killing them as needed, minus the usual reboot.

Command Line Software Update

To list all currently available software packages, type...  

sudo softwareupdate -l

And to install all available updates, type...  

sudo softwareupdate -i -a

Have any more tips and tricks for an always-on Mac? Be sure to share them below in the comments!

Image via Flickr user The Ticket Collector.

By Matt Braga

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History of the Gopher Protocol (Pre-Technology of HTTP)

What is Gopher? (in an internet context )

Gopher is a protocol system, which in advance of the World Wide Web, allowed server based text files to be hierarchically organised and easily viewed by end users who accessed the server using Gopher applications on remote computers. Initially Gopher browsers could only display text-based files before developments such as HyperGopher, which were able to handle simple graphic formats though they were never used on a widespread basis as by this time the World Wide Web and its Hypertext Transfer Protocol (HTTP) were gaining in popularity, and had similar and more extensive functions.

The origins of the Gopher protocol

The Gopher protocol and original Gopher viewer application were first developed at the University of Minnesota in the early 1990’s as part of the drive to make use of the Internet to enable the simple sharing of documents with people who could be located in institutions on opposite sides of the country or even the world, and to have those documents organised so that similar / related pages would be easily accessible. The value of the Gopher system was enhanced by the development of two systems known as Veronica and Jughead which allowed a user to search across resources stored in Gopher file hierarchies on a global basis. As for the naming of the system, the University of Minnesota sports teams were called the ‘Golden Gophers’ and the sports mascot was thus a large gopher, it has been said that the protocol was named in honour of the mascot, and also as in an assistant who's sent to ‘go for’ things.

What happened to it?

By the mid 1990s the World Wide Web was growing at a huge rate, and given that the Web’s Hypertext Transfer Protocol (HTTP) and its browser Mosaic could match the functions of the Gopher protocol and additionally offer added functions such as hyper linking from within HTML files which brought together related pages more efficiently than Gopher, there was no longer a compelling reason to choose the Gopher system. Another advantage the early Web had over Gopher was the decision of the University of Minnesota not to definitively rule out the option of exercising its intellectual property rights over the Gopher protocol, for any other organisation deciding whether to devote time, effort, and expense to adopting one of the systems the possibility of getting locked into a technology that they could then find themselves being charged for was good reason to prefer the World Wide Web. Most of the files and databases that had been available on Gopher were converted into HTTP compatible formats and made available on the Web, though for the interested it is still possible to access the Gopher root directory at the University of Minnesota and a few other places, but the vast majority of the other Gopher servers on the Net have since gone offline.

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Understanding OSI Model (Network Models)

I have to assume that after reading the title to this week's article you probably let out a low, discerning groan of displeasure. Of all the networking topics that I've ever taught, the OSI model is the one that will generate looks of angst and torture on the faces of students. Some simply tune out and play solitaire, while others shake their heads in the familiar "not this thing again". Still others pretend that there's no time like right now to catch a half-hour of shut-eye. One thing that has never happened is someone's eyes lighting up and them shouting "I love the OSI model!". The reason for this is simple. This is often the first thing that people are ever taught when it comes to networking, and it was probably explained in such a way that they didn't understand it to begin with. A theoretical model is a terrible introduction to the world of networking. The good news for me is that most of you probably already have experience in the field, and will hopefully be able to appreciate how important network models really are.

The OSI model was designed by the International Organization for Standardization as a model for helping different systems communicate. Its important to note than back in the early days of networking, you would usually be tied into a single vendor, since their systems could only communicate with like systems, and multi-vendor networks made life a huge hassle. Back then, you generally bought all IBM or all DEC equipment - once a vendor got that first sale, they knew you were pretty much locked in long term. While good for the vendor, this certainly handcuffed the customer in terms of their ability to make choices based on what best met their needs. The OSI model was developed as an architectural framework to allow different systems to communicate. It is not a set of protocols or hard and fast rules. Instead, it acts as a set of guidelines for how network communication should take place, which different sections of the model outlining the roles and responsibilities of each section.

So why take this sectional or layered approach? Well, by making each layer responsible for a different part of the communications process, we make it such that a particular portion can be changed without affecting the other independent parts. So why should you care? Because the OSI model is actually less theoretical than you think. We're ultimately going to take a look at how a packet is built, and this related directly to the model itself. What starts off as data has to somehow be transmitted over the network, meaning that information has to be added to account for the network technologies in use, the addressing and routing of packets, the reliability of the transfer, the actual way data is formatted, how the process is initiated, and so forth. The OSI model actually maps to the packet generation process, and if you always keep that in mind, you'll be well on your way to truly understanding how network communication takes place. Without this knowledge, you might as well forget the whole networking career thing, because this is fundamentally the single most important networking concept you'll ever learn. Yup, ever more important than subnetting…

Every model has a different purpose. The Cisco hierarchical network design model is not concerned with the actual communication process between systems, but rather how network systems should be designed to ensure that the network is designed efficiently and effectively. This model will be covered in the next article in the series.

The OSI Model

Most of you are probably already familiar with the concept of the OSI model and its 7 layers. Each of those layers has a responsibility, important not only conceptually but also in reality. The 7 layers of the OSI model are numbered from bottom to top as follows:

Layer 7 = Application Layer
Layer 6 = Presentation Layer
Layer 5 = Session Layer
Layer 4 = Transport Layer
Layer 3 = Network Layer
Layer 2 = Data Link Layer
Layer 1 = Physical Layer

It is important to know the order and names of the layers above. To make things easy, I usually suggest creating a mnemonic to remember them. The phrase that I originally learned was All People Seem To Need Data Processing (APSTNDP), with each word representing a layer. In the beginning remembering the model can be tricky, but once you truly understand it, you'll never need to think about it again.

The function of the layers needs to be outlined, and you've probably heard this all a hundred times before. The important thing is that we can ultimately relate it all to the packet creation process, which we'll do shortly.

Application Layer - The application layer is the top level of the OSI model. Put simply, this is the layer where users actually interact with applications that create the data that will be sent over the network. Imagine you're using a web browser. You type in www.2000trainers.com, and magically a whole lot of data comes your way. The web browser doesn't participate in the actual obtaining of the data. It simple makes a request (this part is data) saying ‘hey, I need to view this certain web page' the lower layers actually take care of the rest of the request, and making sure that the data requested is actually passed back to the web browser. What the browser is more specifically doing is making a request that a web server will understand - an application on another system. Examples of application-layer programs include web browsers, ftp programs, telnet, email, and so forth. The user interacts with these directly.

Presentation Layer - Layer 6 of the OSI model is concerned with the actual format that the data is presented in. It is important to note that different systems have different ways of formatting data, and in order to ‘see' things properly, the systems have to agree on a way that data will be displayed. For example, data is often encoded using different schemes, such as ASCII, EBCIDC or UNICODE. If one system formats data using a scheme that the other doesn't understand, you're might just be staring a screen full of unrecognisable characters, and that wouldn't do you much good. This layer is home to a number of data presentation standards that you might already be familiar with, including JPG, GIF, and MPEG. However, this layer is also usually responsible for data encryption and compression.

Session Layer - Layer 5 of the OSI model is one that people always seem to have trouble with, mainly because in reality, protocols suites are often developed such that they don't map directly to the OSI model. The responsibility of this layer is to create, manage, and terminate communication sessions between systems. Think of the session layer as a coordinator of communication between systems and you would be on the right track. A variety of protocols exist at the session layer, including Remote Procedure Calls (RPCs), the Network File System (NFS), SQL, and the AppleTalk Zone Information Protocol (ZIP).

Transport Layer - Layer 4 of the OSI model brings us to a place where the actual roles and responsibilities start to get a little more concrete for people. Its responsibilities include segmenting data that comes from the upper layers, establishing a connection between end-to-end systems that defines the parameters of the connection, and ensuring that data actually gets to its destination in the correct order and error free. One way that it does this is by requiring acknowledgements from the receiver for each packet transmitted. Generally, if the packets sent don't get to the destination, the sender will never receive an acknowledgement, and will resend the data. At this layer, systems also agree on how much data should be sent at a time, a process often referred to as windowing, which will be discussed in a future article in more detail. Beyond that, this layer also handles something called flow-control - a process by which the receiving system can tell the sender to slow down, as it may be receiving data more quickly that it can process it. Examples of protocols found at this layer include TCP, UDP, and SPX.

Network Layer - Layer 3 of the OSI model is responsible for two key functions - logical addressing and routing. This layer identifies systems uniquely on our internetwork, and also handles how to get from one part of the network to another. This is the layer where most of the network configuration takes place, since protocols such as IP, IPX, and equipment such as routers work here. This layer doesn't concern itself with reliability of the data transfer, since that's the responsibility of the Transport layer. Its concern is more along the lines of ‘where am I going (the address), and how do I get there (the routing).

Data Link Layer - Layer 2 of the OSI Model is concerned with how upper level data is formatted for transmission over a given network technology. For example, if your network is running Ethernet, this layer will format the data accordingly, and follow the rules of Ethernet transmission on the network. Over the course of being transmitted over a large internetworking, the layer may change many times between the source and destination - the journey might start on Ethernet, move over an ATM network, and then end on a Token Ring LAN. The process of getting across those networks might involve a number of Data Link layer changes to the packet on even a short trip. This layer is actually made up of 2 sub-layers, one called the MAC (Media Access Control), which controls accessing the physical network media, and the other called the LLC (Logical Link Control), whose responsibility is identifying and interacting with the upper-level Layer 3 protocol being used. Examples of Data Link protocols include a variety of network communication standards - Ethernet, Token Ring, FDDI and so forth. At this layer, systems are generally identified by what is referred to as their hardware or MAC address.

Physical Layer - Layer 1 of the OSI model is generally the easiest to identify, because it defines the actual media and characteristics used to send the 1's and 0's over the network. This includes the actual wiring itself, the connectors used, voltage levels, maximum media distances and so forth. The physical layer doesn't change the actual data, although the transmission mechanism itself can vary greatly over the course of transferring data. For example, it might start on twisted-pair wiring, move onto a wireless network, and then ultimately end up on fibre - each of which using different media and methods during the transfer process. In this case, copper wiring, then air, and then fibre optic cable.

The Packet Creation Process

So who cares? Good question. The OSI model is all-to-often described without any perspective of why this stuff is actually important. The answer is simple if you just take the time to put it all together in a reasonable scenario; it truly explains what happens when 2 systems actually communicate. The key to understanding the model is to look at it with respect to how a packet is built on the source system and then stripped apart at the receiving end. This process is referred to as data encapsulation.

Data encapsulation is the process by which a packet is built. It all begins which a chunk of data from the application layer. Maybe you want to view a web page or send a file over the network to another system. In order to get to that other system, information will need to be added to the data to account for reliability, how its going to get to where it needs to go, and the network technology in use.

When looking at the OSI model, the 7 Layers are often grouped into 2 main sections. The top section, comprised of the Application, Presentation and Session Layers, are often referred to as the Application layers, while the bottom four are often generically referred to as the Transport layers. For the purpose of looking at the data encapsulation process, the Applications layers are generally considered to simply pass data, while the Transport layers actually ‘add' to the data to help prepare it to make its way across the network.

Remember that the chunk of data is passed down the layers for formatting. Once it reaches the transport layer, it makes its first big change, usually in the form of header and trailer data being added. At each subsequent layer (except the physical layer, which doesn't change the packet) more header and trailer data is added again. This process is referred to as encapsulation, which each layer literally adding to the packet building process.

A key thing to understand is that as each layer receives the packet and adds to it, it considers everything passes down to it as simple data. That is, whatever the transport layer adds is not of concern to the network layer, and so forth. In that way, each lower layer simply considers what is being passed down to it as data. Consider the diagram below, which outlines how each of these layers changes the data (for clarity purposes, I've left off the trailer additions).

What happens above is easily explained, even though the diagram is highly simplified. Once data is passed to the transport layer, it adds header (and trailer, not shown) information to the data. If this were a TCP/IP packet, that would include TCP or UDP source and destination port information. The network layer would see this all as data, not concerned with what was added. Instead, it would encapsulate the data with another header, which would involve adding the source and destination IP addresses. When passed down to the Data Link layer, still another header would be added - in the case of an Ethernet network, this would include the source and destination MAC addresses. This would then be passed to the Physical layer, in the form of binary data being transmitted across the network.

At the receiving end, the data would subsequently by de-encapsulated, layer by layer in the opposite direction. For example, the receiving station would receive the data stream and pass it up to the data link layer.

1. If this station noticed that its MAC address were the destination MAC address, it would know that it has to pay attention and process the packet, striping off the data link header and passing it up to the network layer. If not, it would simply discard the packet at this point.

2. Next, it will pass the packet up to the Network Layer. At this point, it will determine whether the destination IP address is its IP address. If so, it will strip off the network header and pass it up to the transport layer. You should note that just because the MAC address belongs to the system, it doesn't necessarily mean that the IP address does as well. For example, a router will receive many packets with its MAC address and different IP destination addresses, a subject we'll broach once we get into routing.

3. Once the packet has been passed up to the Transport layer, it is definitely destined for this system. This layer will take a look at the destination port listed in the header, strip the header, and then pass the data to the appropriate application that is waiting for the data, assuming that application exists (it may not - imaging a request for a web page from a system not running as a web server)

Note that at each point in the process, a layer only looks at the information added by its equivalent layer at the sending machine. To that end, the only layers that a given layer ever interacts with are the equivalent layers on other systems, as well as the layers directly above and below it on the same system. The fact that layers are independent of each other is another design goal of the OSI model - changing a given layer should not effect other layers in the model

One last note with respect to the encapsulation process described above. As each layer changes the data, the reference name for that data unit is changed. ‘Packet' is a generic name often used to describe the unit at any stage of the process. However, the following terms are commonly used to describe data at different network layers:

Data units above the Transport layer = Messages

Transport layer data units = Segments

Network layer data units = Datagrams or Packets

Data Link layer data units = Frames

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The OSI Model's Seven Layers Defined and Functions Explained

The Open Systems Interconnect (OSI) model has seven layers. This article describes and explains them, beginning with the 'lowest' in the hierarchy (the physical) and proceeding to the 'highest' (the application). The layers are stacked this way:

• Application
• Presentation
• Session
• Transport
• Network
• Data Link
• Physical

PHYSICAL LAYER

The physical layer, the lowest layer of the OSI model, is concerned with the transmission and reception of the unstructured raw bit stream over a physical medium. It describes the electrical/optical, mechanical, and functional interfaces to the physical medium, and carries the signals for all of the higher layers. It provides:

• Data encoding: modifies the simple digital signal pattern (1s and 0s) used by the PC to better accommodate the characteristics of the physical medium, and to aid in bit and frame synchronization. It determines:
  
  
  • What signal state represents a binary 1
  • How the receiving station knows when a "bit-time" starts
  • How the receiving station delimits a frame
• Physical medium attachment, accommodating various possibilities in the medium:
  
  
  • Will an external transceiver (MAU) be used to connect to the medium?
  • How many pins do the connectors have and what is each pin used for?
• Transmission technique: determines whether the encoded bits will be transmitted by baseband (digital) or broadband (analog) signaling.
• Physical medium transmission: transmits bits as electrical or optical signals appropriate for the physical medium, and determines:
  
  
  • What physical medium options can be used
  • How many volts/db should be used to represent a given signal state, using a given physical medium

DATA LINK LAYER

The data link layer provides error-free transfer of data frames from one node to another over the physical layer, allowing layers above it to assume virtually error-free transmission over the link. To do this, the data link layer provides:

• Link establishment and termination: establishes and terminates the logical link between two nodes.
• Frame traffic control: tells the transmitting node to "back-off" when no frame buffers are available.
• Frame sequencing: transmits/receives frames sequentially.
• Frame acknowledgment: provides/expects frame acknowledgments. Detects and recovers from errors that occur in the physical layer by retransmitting non-acknowledged frames and handling duplicate frame receipt.
• Frame delimiting: creates and recognizes frame boundaries.
• Frame error checking: checks received frames for integrity.
• Media access management: determines when the node "has the right" to use the physical medium.

NETWORK LAYER

The network layer controls the operation of the subnet, deciding which physical path the data should take based on network conditions, priority of service, and other factors. It provides:

• Routing: routes frames among networks.
• Subnet traffic control: routers (network layer intermediate systems) can instruct a sending station to "throttle back" its frame transmission when the router's buffer fills up.
• Frame fragmentation: if it determines that a downstream router's maximum transmission unit (MTU) size is less than the frame size, a router can fragment a frame for transmission and re-assembly at the destination station.
• Logical-physical address mapping: translates logical addresses, or names, into physical addresses.
• Subnet usage accounting: has accounting functions to keep track of frames forwarded by subnet intermediate systems, to produce billing information.

Communications Subnet

The network layer software must build headers so that the network layer software residing in the subnet intermediate systems can recognize them and use them to route data to the destination address.

This layer relieves the upper layers of the need to know anything about the data transmission and intermediate switching technologies used to connect systems. It establishes, maintains and terminates connections across the intervening communications facility (one or several intermediate systems in the communication subnet).

In the network layer and the layers below, peer protocols exist between a node and its immediate neighbor, but the neighbor may be a node through which data is routed, not the destination station. The source and destination stations may be separated by many intermediate systems.

TRANSPORT LAYER

The transport layer ensures that messages are delivered error-free, in sequence, and with no losses or duplications. It relieves the higher layer protocols from any concern with the transfer of data between them and their peers.

The size and complexity of a transport protocol depends on the type of service it can get from the network layer. For a reliable network layer with virtual circuit capability, a minimal transport layer is required. If the network layer is unreliable and/or only supports datagrams, the transport protocol should include extensive error detection and recovery.

The transport layer provides:

• Message segmentation: accepts a message from the (session) layer above it, splits the message into smaller units (if not already small enough), and passes the smaller units down to the network layer. The transport layer at the destination station reassembles the message.
• Message acknowledgment: provides reliable end-to-end message delivery with acknowledgments.
• Message traffic control: tells the transmitting station to "back-off" when no message buffers are available.
• Session multiplexing: multiplexes several message streams, or sessions onto one logical link and keeps track of which messages belong to which sessions (see session layer).

Typically, the transport layer can accept relatively large messages, but there are strict message size limits imposed by the network (or lower) layer. Consequently, the transport layer must break up the messages into smaller units, or frames, prepending a header to each frame.

The transport layer header information must then include control information, such as message start and message end flags, to enable the transport layer on the other end to recognize message boundaries. In addition, if the lower layers do not maintain sequence, the transport header must contain sequence information to enable the transport layer on the receiving end to get the pieces back together in the right order before handing the received message up to the layer above.

End-to-end layers

Unlike the lower "subnet" layers whose protocol is between immediately adjacent nodes, the transport layer and the layers above are true "source to destination" or end-to-end layers, and are not concerned with the details of the underlying communications facility. Transport layer software (and software above it) on the source station carries on a conversation with similar software on the destination station by using message headers and control messages.

SESSION LAYER

The session layer allows session establishment between processes running on different stations. It provides:

• Session establishment, maintenance and termination: allows two application processes on different machines to establish, use and terminate a connection, called a session.
• Session support: performs the functions that allow these processes to communicate over the network, performing security, name recognition, logging, and so on.

PRESENTATION LAYER

The presentation layer formats the data to be presented to the application layer. It can be viewed as the translator for the network. This layer may translate data from a format used by the application layer into a common format at the sending station, then translate the common format to a format known to the application layer at the receiving station.

The presentation layer provides:

• Character code translation: for example, ASCII to EBCDIC.
• Data conversion: bit order, CR-CR/LF, integer-floating point, and so on.
• Data compression: reduces the number of bits that need to be transmitted on the network.
• Data encryption: encrypt data for security purposes. For example, password encryption.

APPLICATION LAYER

The application layer serves as the window for users and application processes to access network services. This layer contains a variety of commonly needed functions:

• Resource sharing and device redirection
• Remote file access
• Remote printer access
• Inter-process communication
• Network management
• Directory services
• Electronic messaging (such as mail)
• Network virtual terminals

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NetSim network simulator software for Cisco certification practice

Boson has been developing simulator software for about four years, and the current release of its NetSim product shows that the investment in time and money was well spent. Boson's NetSim has one of the widest selections of simulated equipment aside from Gambit’s Cisco simulator. And for the price, no one else offers anything close to NetSim's features. My following review of NetSim explains all the simulation software features you get for a miserly $150 to $250.

NetSim versions

There are two versions of NetSim. There is a current version called Cisco CCNA Network Simulator v5.00, which is also packaged and sold by Cisco Systems as part of its CCNA training material. This CCNA version is $150 and offers a credit to the full version if you decide to upgrade at a later date. In late July 2004, there will be a new CCNP version released called Boson NetSim for CCNP v6.00. This version will have the full feature set that allows coverage of the CCNP track and will support, to a degree, the CCIE track. The big difference between the two versions is the advanced commands (such as routing protocol BGP) will be supported and enabled in the CCNP version. Boson is also offering upgrades to anyone with V5.x of its NetSim product to the new version 6.

The following are sample labs included with NetSim version 5.00:

• Introductory labs such as using debug, the Command Line Interface (CLI), and configuring the router
• Moderately complex labs such as ARP, static routes, protocols, and PPP with CHAP
• VLSM labs to practice your TCP/IP subnet skills
• VLAN labs such as configuring VLANs and routing between VLANs
• VTP labs to explain and demonstrate what VTP is and how to configure it
• Loopback labs
• Routing Protocol labs including RIP, IGRP, and OSPF (BGP in the CCNP)
• IPX labs
• Frame Relay labs
• Access List labs, both Standard lists and Extended lists
• ISDN labs
• Labs needed to meet the Cisco CCNA and ICND requirements

System requirements

The system requirements for NetSim are pretty light considering what is going on in the background. The basic requirements are:

• Windows 98, Me, NT4, 2000, XP (non-server product)
• 20 MB of disk space
• 64 MB of RAM
• 800 x 600 screen resolution
• Active Internet connection (for registration)

My testing was conducted on Windows 98, Windows 2000, and Windows XP Pro operating systems. While 98 will work with NetSim, it is slow in regards to response time. The platforms used were an older PIII 800 with 576 MB of RAM and a new P4 2.8-GHz with 512 MB of RAM. NetSim does require Microsoft MDAC 2.8 to be installed, so you might have to download the components from the Microsoft Windows support Web site.

Using the NetSim interface

There are several ways to use either the CCNA or the CCNP NetSim product. One way is to work through the various labs that are included. The second way is to design your own labs and network configurations. Another unique feature of the NetSim product is that you can also use third-party telnet clients. These clients include TeraTerm, Absolute Telnet, Telnet 2000, TinyTerm, among others. In Figure A, you can see TeraTerm being used as the telnet application. This method can be very helpful since TeraTerm can be configured to log the entire session, so you can go back and study everything you did, step by step.

Figure A

You can use TeraTerm as a telnet client to work in NetSim.

In Figure B, you see the complete NetSim workspace with a Network map loaded showing two 3600 series routers and a 3500 switch. You can also see the two open telnet sessions.

Figure B

This screen shows the Expert mode where the majority of users will be the most comfortable.

NetSim features

There is a feature of NetSim that sets it apart from virtually all of the other simulators with the exception of Gambit's MIMIC and eRouter. NetSim uses a technology called Virtual Packets that creates packets to be routed and switched within the simulated network. This feature allows NetSim to build a virtual routing table for each protocol and gives flexibility to the CCNA far beyond the standard simulator fare.

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Note

Virtual Packets requires opening up loopback address 127.0.0.1 on personal firewalls such as ZoneAlarm and allowing Telnet Port 23 access to the loopback network. I used Kerio's Personal Firewall on one of the test systems and, once I configured NetSim as a Trusted Network, no problems arose. The printed manual gives instructions for configuring Norton Personal Firewall and ZoneAlarm.

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Some other notable features include:

• The ability to use canned labs or to build your own and save them for future use.
• The option to load in real router configurations, which is handy because you can save the configurations without having to save the entire lab. When you mock up a solution for a real world problem you can load the saved configurations into your equipment.
• When you are in a telnet session, you can use the hot key combination of CTRL-Q and bring up a terminal server so you can quickly shift among all the different devices.
• When you configure a device like a 3600 series router, you can pick and choose which cards will be put into what slot. The hardware configuration is dynamic, so you can match existing hardware or work with different configurations.
• When using the CLI of the router or switch, the newest version of NetSim has corrected a known issue whereby the ^ symbol did not match up with the error on the command line.
• Unlike some other products, this product is not vendor specific where you can only use certain labs or books.

Upcoming features

One of the benefits of being a technical writer is that software developers like to tell me what they are working on next. In the case of NetSim’s development team, they are busy to say the least. Take a quick look at some of the features due out in the coming months for NetSim:

• Boson NetSim Lab Compiler – This will allow teachers to write and compile their own labs into the NetSim framework. These labs can be distributed to the students or posted to a Web site for downloads. This would also open things up for something like a "CCNP Challenge" where you could post your own lab and people would come up with a solution in a timed manner.
• Packet Logger – This is a network sniffer that allows you to detect packets on the NetSim network. This feature will open up a lot of possibilities from the networking perspective into how packets work. This is a very exciting development and should be out in September 2004.
• There is also a new classroom management package that allows the instructor to remotely access the student’s lab and help troubleshoot the student’s problems.

Final thoughts

During my testing of NetSim, neither the CCNA or CCNP products locked up or crashed the test systems. The Windows XP system I used is a complete mess of applications and, if anything has a chance of crashing, it will on this system. However, NetSim loaded up fine and worked without a fuss.

For the price, the NetSim product is offering a tremendous amount of value to the CCNA and CCNP candidate. And with some of the new features that have been added, it becomes a network designer tool where you can make a change to a network before you actually touch a console. The included labs are high quality and cover everything that a candidate needs to know to pass the CCNA and CCNP certification tests. With the exception of my Windows 98 client, the responsiveness of NetSim has also been improved from previous versions. With the new features coming out shortly, I would recommend NetSim for any network engineer, whether that engineer is working on a Cisco certification or just needs a tool to help manage and troubleshoot existing networks.

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Learn CCNA with Cisco Packet Tracer

I have been using Cisco Packet Tracer primarily for many of my CCNA labs and I find it to be a great piece of software.  Whether you don’t have access to real Cisco equipment, or you cant afford to purchase some of your own, Packet Tracer is as good as it gets.

I have a home lab that consists of several switches and routers, but I find myself away from home most of the time and cant get enough time at home to lab.  I have Packet Tracer installed on my laptop and I use it all the time to practice configurations and lab concepts.

You can do simple configurations like leased line WAN links using HDLC or PPP encapsulation.  You can also practice some of your more advanced configurations like Frame-Relay and even setup a Frame-Relay cloud that connects multiple sites.

I love the fact that you can actually see what the devices look like and install real world WIC cards like the WIC-1T, WIC-2T and WIC-1ENET.

I also find the CLI is very close to the real thing and only lacking some of the more advanced commands and setting like some Frame-Relay commands (no frame-relay inverse-arp), and setting up OSPF route summarization.

You have the ability to setup client machines of various types like laptops, servers, handheld devices, wireless devices, and even wireless access-points as well

Packet Tracer runs on Windows and Linux systems.  I have it running on Linux using the WINE emulator, but I could install the native version as well.  I find that the Windows version seems to get updated more frequently because its obviously what the majority of Cisco students use, so thats the version I prefer.

Good job Cisco on a awesome learning tool and keep up the great work!

You can download Packet Tracer from the Cisco website, but you must have a Cisco account.

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Install iRedMail on Red Hat Enterprise Linux, CentOS, Scientific Linux

System Requirements

WARNING: iRedMail is designed to be deployed on a FRESH server system, which means your server does NOT have mail related components installed, e.g. MySQL, OpenLDAP, Postfix, Dovecot, Amavisd, etc. Otherwise it may override your existing files/configurations althought it will backup files before modifing, and it may be not working as expected.

To install iRedMail, you need:

• A FRESH, working RHEL, CentOS, Scientific Linux system. Supported releases are listed on page Features of iRedMail.
• At least 512MB of memory is required for production use.

Note: All third-party binary packages will be installed from below yum repositories, packages with '-ired' flag were packed by iRedMail project:

• Dag Wieers: http://packages.sw.be/
• EPEL (Extra Packages for Enterprise Linux): http://download.fedora.redhat.com/pub/epel/
• ATrpms: http://atrpms.net/

Preparations

Set a fully qualified domain name (FQDN) hostname on your server

Enter command 'hostname -f' to view the current hostname:

$ hostname -f
demo.iredmail.org

On RHEL/CentOS/Scientific Linux, hostname is set in two files:

• /etc/sysconfig/network: hostname setting

# Part of file: /etc/sysconfig/network
HOSTNAME=demo.iredmail.org

• /etc/hosts: hostname <=> IP address mapping. Warning: List the FQDN hostname as first item.

# Part of file: /etc/hosts
127.0.0.1   demo.iredmail.org demo localhost localhost.localdomain

Verify the FQDN hostname. If it wasn't changed, please reboot server to make it work.

$ hostname -f
demo.iredmail.org

Enable yum repositories for installing new packages

• For CentOS or Scientific Linux, please enable CentOS/Scientific official yum repositories, and DISABLE all third-party yum repositories to avoid package conflict.
• For Red Hat Enterprise Linux, please enable Red Hat Network to install packages, or create a local yum repository with DVD/CD ISO images.

Download the latest release of iRedMail

• Visit Download page to get the latest release of iRedMail.
• Upload iRedMail to your mail server via ftp or scp or whatever method you can use, login to the server to install iRedMail. We assume you uploaded it to directory /root/iRedMail-x.y.z.tar.bz2 (replace x.y.z by the actual version number).
• Uncompress iRedMail tarball:

# cd /root/
# tar xjf iRedMail-x.y.z.tar.bz2

Start iRedMail installer

It's now ready to start iRedMail installer, it will ask you some simple questions, that's all steps to setup a full-featured mail server.

For Chinese users: Our domain name "iredmail.org" is blocked in China mainland since Jun 04, 2011, please replace all 'iredmail.org' by its IP address "173.254.22.21" (without quotes) in /root/iRedMail-x.y.z/pkgs/get_all.sh BEFORE executing "iRedMail.sh".

# cd /root/iRedMail-x.y.z/
# bash iRedMail.sh

Screenshots of installation:
1) Welcome and thanks for your use




2) Specify location to store all mailboxes. Default is /var/vmail/.





3) Choose backend used to store mail accounts. Please choose the one which you're familiar with. You can manage mail accounts with iRedAdmin, our web-based iRedMail admin panel.





4) If you choose to store mail accounts in OpenLDAP, iRedMail installer will ask you two questions about OpenLDAP.
4.1) LDAP suffix.




4.2) Password of LDAP root dn.




5) Set password of MySQL root user. MySQL is used to store data of other applications, e.g. Roundcube webmail, Policyd, Amavisd-new. If you choose to store mail accounts in MySQL, you will see this dialog too.




6) Add your first mail domain name




 7) Set password of admin account of your first mail domain. Note:

• This account is used only for system administration, not a mail user. That means you CANNOT login to webmail with this account.
• You can login to iRedAdmin (web-based iRedMail admin panel) with this account for mail accont management, login name is full email address.
• Admin username is hard-coded, you can create new admins with iRedAdmin after installation completed.

8) Set password of first mail user of your first mail domain. Note:

• This account is a normal mail user, that means you can login to webmail with this account, login name is full email address.
• Username is hard-coded, you can create new mail users with iRedAdmin after installation completed.

9) Choose optional components




After answered these questions, iRedMail installer will ask your confirm to start installation. It will install and configure required packages automatically. Type 'y' or 'Y' (without quotes) and press 'Enter' to confirm.

Configuration completed.

*************************************************************************
**************************** WARNING ***********************************
*************************************************************************
*                                                                       *
* Please do remember to *REMOVE* configuration file after installation  *
* completed successfully.                                               *
*                                                                       *
*   * /root/iRedMail-x.y.z/config
*                                                                       *
*************************************************************************
<<< iRedMail >>> Continue? [Y|n]        # <- Type 'Y' or 'y' here, and press 'Enter' to continue

 

 

Important things you should know after installation

• Read file /root/iRedMail-x.y.z/iRedMail.tips first, it contains:
  • URLs, usernames and passwords of web-based applications
  • Location of mail serve related software configuration files
  • Some other important and/or sensitive information
  
  
  
• Setup DNS record for SPF
• Setup DNS record for DKIM

Access webmail and other web applications

After installation successfully completed, you can access web-based programs if you choose to install them. Replace 'your_server' below by your actual server name or IP address.

Component	URL	Accessible via HTTP	Accessible via HTTPS
Webmail	http://your_server/mail/ (or /webmail, /roundcube)
iRedAdmin (admin panel)	httpS://your_server/iredadmin/
phpMyAdmin	httpS://your_server/phpmyadmin/
phpLDAPadmin	httpS://your_server/phpldapadmin/
Awstats	httpS://your_server/awstats/awstats.pl?config=web (or ?config=smtp)

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Windows server 2008 r2 forgot administrator password

Forgot Windows Password, hack windows password, Windows Password Reset

I forgot administrator password of windows server 2008 r2. I have no idea on log on that server without administrator password. Does somebody tell me how to recover the lost password for my win server 2008? – Question from Microsoft community.

If we forget the administrator of a windows server 2008 (r2), how to do? This post shows how to reset a lost password for windows server 2008 with password software.

Tips: To reset windows server 2008 (r2) password offline, a USB flash drive or a CD/DVD burn device and a blank CD/DVD is need.

1. Reset windows server 2008 administrator password with Spower Password Reset Special.

Tips: this method not only work to reset windows server 2008 domain administrator password, but also work with a local administrator password on windows server 2008 (r2).

Spower Windows Password Reset Special can help to reset local and domain password for windows 2000/xp/2003/vista/win7/2008 without any password.

Follow the instructions below to make a 2008 password disk, and reset a new password to the administrator user with the password disk.

• Step 1: Download Spower Password Reset Special (trial version) and install it on a windows (windows 7, vista, xp, 2000 or 2008).
• Step 2: Launch Spower Password Reset Special, and insert USB flash drive or CD/DVD disc to create a windows 2008 password disk.

• 

• Step 3: Boot the locked windows server computer from windows 2008 password disk.
• Step 4: Reset windows 2008 domain administrator password with the Spower Password Program – Select the administrator account, and click the reset button to reset a new password to it..

• 

 

2. Reset windows server 2008 local administrator password with Windows Password Rescuer Advanced (WPRA).

With Windows Password Rescuer Professional, the administrator password can be reset in a few click. Step as follow:

• 1. Download Windows Password Rescuer Advanced (trial version) and install it.
• 2. Make a 2008 password reset disk with WPRP. Insert a USB or CD disk, and click the burn button to make a password disk.
• 3. Boot the locked windows server computer from 2008 password reset disk.
• 4. Reset the lost password for administrator. Click administrator account to make it selected, and then click reset button to create a new password for it.

Tags: windows server 2008 r2 forgot administrator password

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Hack Windows 7 password with Ophcrack live cd

hack windows 7 password, hack windows password, Ophcrack

 

http://linux-mac-windows.blogspot.com/2012/08/how-to-hack-password-on-windows-7-with.html

With Ophcrack live cd, we can recover Windows  7, vista and xp password easily. Here shows you the step by step tutorial to hack windows 7 password with Ophcrack.

Something about Ophcrack . Ophcrack is a free open source windows password hack program. Ophcrack hack windows password using  by using rainbow tables.

What Ophcrack live cd can do.  Ophcrack live cd can help you recover windows the most lost windows password. With free Ophcrack live cd which has a default rainbow table can help to crack short Windows password in a few minutes. If you want to hack long windows password, you need to buy one or more large (larger then 10G) rainbow tables.

Note: You have to know, even with the largest rainbow tables , still many passwords cannot be crack in windows vista and windows 7.

How Ophcrack works.  Ophcrack is known as cracking windows password through big rainbow tables. Ophcrack read LM or NTLM hashes from SAM file, and then it find the hash value in rainbow tables.  So the more complex password need the larger rainbow table to crack.

Get Ophcrack live cd. Ophcrack has two different live cds for different Windows system, one for Windows xp, one for Windows vista and Windows 7. To hack Windows 7 password, we need to download ophcrack Vista LiveCD.

What you download will be an ISO file – ophcrack-vista-livecd-2.3.1.iso.

Use Ophcrack live cd to hack Windows 7 password. If have downloaded Ophcrack Vista LiveCD, follow the steps below to hack windows 7 password.

Step 1 – Burn Ophcrack Vista Live CD to a CD or DVD disc. Use a ISO file burn program to burn the ophcrack-vista-livecd-2.3.1.iso to the cd or dvd disc. Note: You cannot burn the iso file to the cd or dvd disc like burning a common file.  You should use the Burn ISO Image option the burn program provides to burn the iso file to cd or dvd disc, or you will fail to boot the computer from Ophcrack Vista Live CD. If you have trouble in this operation, you can refer to How to burn ISO image file to CD/DVD disc.

Step 2 – Boot the computer which will be hacked from Ophcrack Vista Live CD. Note: The following steps should happen on the computer you want to hack, instead happen on the computer you are using.
2.1 Insert Ophcrack Vista Live CD to the computer.

2.2 Access to BIOS Setup Utility to Set the CD/DVD-ROM as the first boot device.
2.3 Press 10 to save BIOS setting and then restart computer.

Tip: If you fail to boot from Ophcrack Vista Live CD, you should check whether you used the right way to burn the ISO file to CD/DVD disc, and check whether you have set the computer to boot from CD/DVD-ROM.




Step 3 – Get the password has been hacked by Ophcrack. After boot from Ophcrack Vista Live CD, you do not need to do anything. What you should just do is write down the password has been hack. The user column will list the user Ophcrack find in system. The NT Pwd column will list the password has been found. If the NT Pwd field is empty for a special user, the password has not been found yet.



Tip: If Ophcrack fail to find the password for you, you can try other password reset/recover software. Refer to How to hack windows 7 admin password in a few minutes for using another software to hack windows 7 password.


Step 4 – Resart Windows and login with the recovered password. Press the restart button of your computer or click Menu -> Logout -> Reboot system to restart computer, and then login with the hacked password.

Reference site:

•  http://ophcrack.sourceforge.net/
• http://en.wikipedia.org/wiki/Ophcrack

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