CCNA Certification Exam Tutorial: Cisco Switching Modes

 


Visitors: 410

To pass the CCNA exam and earn this important certification, you’ve got to know switching inside and out. While you’re learning all the basic switching theory, make sure to spend some time with the one of three switching modes Cisco routers can use.

Store-and-Forward is exactly what it sounds like. The entire frame will be stored before it is forwarded. This mode allows for the greatest amount of error checking, since a CRC (Cyclical Redundancy Check) is run against the frame before it is forwarded. If the frame contains an error, it is discarded. If there’s no problem with the frame, the frame is then forwarded to its proper destination.

While store-and-forward does perform error checking, the delay in processing the frame while this error check is run results in higher latency than the other modes you’re about to read about. The latency time can also vary, since not all frames are the same size.

Cut-through switching copies only the destination MAC address into its memory before beginning to forward the frame. Since the frame is being forwarded as soon as the destination MAC is read, there is less latency than store-and-forward. The drawback is that there is no error checking.

There is a middle ground, fragment-free switching. Only part of the frame is copied to memory before it is forwarded, but it’s the first 64 bytes of the frame, not just the destination MAC. (Why? Because if there is a problem with the frame, it’s most likely in the first 64 bytes. ) There is a little more error checking than cut-through, but not as much latency as with store-and-forward.

Note that the latency of both cut-through and fragment-free is fixed; these modes always look at the first six or 64 bytes, respectively. Store-and-forward's latency depends on the size of the frame.

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.

You can also join his RSS feed and visit his blog, which is updated several times daily with new Cisco certification articles, free tutorials, and daily CCNA / CCNP exam questions! Details are on the website.

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!

(443)

Article Source:


 
Rate this Article: 
 
Cisco CCNA Certification Exam Tutorial: Distance Vector Command Review
Rated 4 / 5
based on 5 votes
ArticleSlash

Related Articles:

Cisco CCNA Certification Exam Tutorial: RIP Details You Must Know

by: Chris Bryant (April 13, 2006) 
(Computers and Technology/Certification Tests)

Cisco CCNA Certification Exam Tutorial: The OSPF RID

by: Chris Bryant (April 08, 2006) 
(Computers and Technology/Certification Tests)

Cisco CCNA Certification Exam Tutorial: ISDN Details You Must Know

by: Chris Bryant (April 18, 2006) 
(Computers and Technology/Certification Tests)

Cisco CCNA Certification Exam Tutorial: Keep Your Most Important Appointment

by: Chris Bryant (May 09, 2006) 
(Computers and Technology/Certification Tests)

Cisco CCNA Certification Exam Tutorial: Configuring And Troubleshooting VTP

by: Chris Bryant (May 04, 2006) 
(Computers and Technology/Certification Tests)

Cisco CCNA Certification Exam Tutorial: Configuring Dialer Profiles

by: Chris Bryant (April 25, 2006) 
(Computers and Technology/Certification Tests)

Cisco CCNA Certification Exam Tutorial: DNS And The IP Name-Server Command

by: Chris Bryant (April 01, 2006) 
(Computers and Technology/Certification Tests)

Cisco CCNA Certification Exam Tutorial: Access List Details You Must Know!

by: Chris Bryant (April 29, 2006) 
(Computers and Technology/Certification Tests)

Cisco CCNA-CCNP Certification Exam Tutorial: EIGRP And Split Horizon

by: Chris Bryant (February 07, 2007) 
(Computers and Technology)

Cisco CCNA Certification Exam Tutorial: Distance Vector Command Review

by: Chris Bryant (May 08, 2006) 
(Computers and Technology/Certification Tests)