After you’ve finally recovered from the shock of your hard drive
crash, you’ll have to begin the process of recovering your
files. It’s not a fun task, but somebody has to do it. You can
pay a lot of money to hire the expertise, or you can do it
yourself using software made especially for this type of
situation.

Take a bit of comfort knowing that if there’s software to handle
this situation, you’re not alone in needing it! It’s important
to understand that there are different levels of corruption that
can occur on your computer.

You can have a complete hard drive failure which will
disintegrate everything installed on your system. Then there is
individual file corruption which can still ruin your day.

When an individual file is corrupted, it means that the program
that manages the file is unable to access it. Without access,
the file becomes corrupted. There are many ways a file can
become corrupted.

There might be a bad spot on your hard drive that the file
attempted to write to. There are diagnostic programs you can run
periodically to fix these bad spots, but most small business
owners just don’t do that. If the bad spots are not fixed, and
the file gets written to it or partially written to it, that
file is officially corrupted. (However, you probably won’t know
this until the next time you go to open that file!)

Power surges are another big culprit involved in corrupting
files. If a power surge strikes at the moment you are attempting
to open a file, close a file or write to a file, the file will
become corrupted.

Accidentally kicking the big, red power switch on your CPU
likely will corrupt whatever files were open at that time.
Viruses are notorious for wreaking havoc on your files as are
any number of other unexpected and unexplainable gremlins that
attach to your pc on a daily basis.

Many small businesses depend upon the Microsoft Access database
management system to manage their accounting or their inventory,
or their CRM and any number of other business applications which
are database dependent. Imagine how you would feel if one day
you went to enter in a customer’s order and found that
everything you needed to process that order - your customers,
your product and pricing, and even your inventory - was all
gone! How could you recoup?

Or you go to open Microsoft Word and try to open the sales
presentation you’ve been working tirelessly on, and the file
can’t be read. How much money could you potentially lose by not
having that presentation submitted on time, thereby losing the
opportunity to compete for a lucrative project? A situation such
as this could actually put a small business out of business.

And what about those huge, number-crunching spreadsheets you’ve
put together in MS-Excel? You know, the ones that contain all of
your crucial accounting, sales projection, and other financial
data? What would you do if they were lost and you had to
recreate them? Could you recreate them?

There is a way your MS-Access, MS-Word and MS-Excel files can
recover from CFS, in as little as fifteen minutes. That’s right.
All you need is a prescription for OfficeFIX, a file recovery
suite that can fix your damaged MS-Excel files (works on all
versions of Excel), your MS-Access files (version 95, 97, 2000,
XP, and 2003) and your MS-Word files (works on all versions
including Word for Macintosh).

So rest assured knowing that when the dreaded CFS strikes your
business, there’s help!

Passing the CCNA, Intro, and ICND exam is all about knowing and noticing the details. (Which makes perfect sense, since becoming a master networking administrator or engineer is also about noticing the details!) One such detail knows the difference between error detection and error recovery. While the terms are sometimes used interchangeably, they are not the same thing.

Error detection is just that - error detection only. Two common error detection methods are found at the Data Link layer of the OSI model, the FCS (Frame Check Sequence) and CRC (Cyclical Redundancy Check). A mathematical equation is run against the data in the frame, and the result is sent along with the data. The receiver runs the equation again, but this time. If the result is the same, the frame is considered valid; if the result is different, the frame is considered corrupt and is discarded.

Note that the FCS and CRC do nothing in regards to retransmission. They are strictly error detection schemes.

For an example of error recovery, we look to the Transport layer, where TCP runs. TCP performs reliable delivery, and the reason we call it “reliable” is that TCP uses sequence numbers to detect missing segments. If the sender determines from the sequence numbers that the remote host did not receive transmitted segments, the sender will retransmit the missing segments.

The key to keeping the terms straight in your head is to remember that while both error detection and error recovery both detect problems, only error recovery does anything about it. It’s also worth reading an exam question twice when you see either term!

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.
For a FREE copy of his latest e-books, “How To Pass The CCNA” and “How To Pass The CCNP”, visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! Pass the CCNA exam with The Bryant Advantage!

Passing the CCNA is tough, and one of the toughest parts is keeping all the acronyms straight! Frame Relay has plenty of those, and today we’re going to examine what DLCIs do and how they’re mapped on a Cisco router.

Frame Relay VCs use Data-Link Connection Identifiers (DLCI - pronounced “del-see”) as their addresses. Unlike other Cisco technologies, VCs have only a single DLCI in their header. They do not have a source and destination.

DLCIs have local significance only. DLCI numbers are not advertised to other routers, and other routers can use the same DLCI numbers without causing connectivity issues.

Cisco uses the term global addressing to describe a technique by which a router in a frame relay network is reached via the same DLCI number from each router in the network. For example, in a 25-router network, the same DLCI number would be used to reach “Router A” by each router.

Global Addressing is an organizational tool that does not affect the fact that DLCIs have local significance only.

The locally significant DLCI must be mapped to the destination router’s IP address. There are two options for this, Inverse ARP and static mapping.

In both of the following examples, the single physical Serial interface on Router 1 is configured with two logical connections through the frame relay cloud, one to Router 2 and one to Router 3.

Inverse ARP runs by default once Frame Relay is enabled, and starts working as soon as you open the interface. By running show frame-relay map after enabling Frame Relay, two dynamic mappings are shown on this router. If a dynamic mapping is shown, Inverse ARP performed it.

R1#show frame map

Serial0 (up): ip 200.1.1.2 dlci 122(0×7A,0×1CA0), dynamic,

broadcast,, status defined, active

Serial0 (up): ip 200.1.1.3 dlci 123(0×7B,0×1CB0), dynamic,

broadcast,, status defined, active

Static mappings require the use of a frame map statement. To use static mappings, turn Inverse ARP off with the no frame-relay inverse-arp statement, and configure a frame map statement for each remote destination that maps the local DLCI to the remote IP address. Frame Relay requires the broadcast keyword to send broadcasts to the remote device.

R1#conf t

R1(config)#interface serial0

R1(config-if)#no frame-relay inverse-arp

R1(config-if)#frame map ip 200.1.1.2 122 broadcast

R1(config-if)#frame map ip 200.1.1.3 123 broadcast

The syntax of the frame map statement maps the remote IP address to the local DLCI.
Broadcasts will not be transmitted by default; the broadcast option must be configured.

R1#show frame map

Serial0 (up): ip 200.1.1.2 dlci 122(0×7A,0×1CA0), static,

broadcast,

CISCO, status defined, active

Serial0 (up): ip 200.1.1.3 dlci 123(0×7B,0×1CB0), static,

broadcast,

CISCO, status defined, active

Hands-on practice is the best way to prepare for CCNA exam success. Working with Frame Relay in a lab environment practically guarantees that you’ll truly master the concepts shown here - and then you’re on your way to the CCNA and becoming a master network engineer.

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.

For a FREE copy of his latest e-books, “How To Pass The CCNA” and “How To Pass The CCNP”, visit the website and download your free copies. You can also get FREE CCNA and CCNP exam questions every day! Get your CCNA study guide from The Bryant Advantage!