To help you prepare for Cisco certification exam success, here are some free CCNA, Security, CCENT, and CCNP practice exam questions. There's also a free tutorial on Cisco switching methods, so let's get started! CCENT Exam:

Of the three frame processing options on Cisco switches - store-and-forward, cut-through, and fragment-free - identify which one best matches each of the following statements.

A. This is the fastest method of the three.

B. This is the slowest method of the three.

C. This method has the highest level of error detection.

D. This method has the lowest level of error detection.

E. This method is considered the "middle ground" of the three when it comes to error detection and transmission speed.

Answers:

A. cut-through

B. store-and-forward

C. store-and-forward

D. cut-through

E. fragment-free

Here's a look at each method.

When store-and-forward is in use, the switch does indeed store the entire frame before forwarding it, which allows the switch to check the FCS before forwarding that frame. This allows the greatest level of error detection of the three frame processing methods.

With the other two methods, the entire frame will not be stored before forwarding. When the cut-through method is in use, the switch will read the MAC addresses on the incoming frame, and then begin to forward the frame even as part of it is still being received!

The FCS value is not checked, so while cut-through is a faster method of processing frames than store-and-forward, cut-through has no way to check for damaged frames. Cut-through is the fastest of the three processing methods, but it comes at a high cost - no error detection!

Cut-through is very fast, but offers no error detection; store-and-forward does offer error detection via the FCS check, but isn't as fast as cut-though. Happily, there's a middle ground - fragment-free.

Fragment-free processing works on the presumption that if a frame is corrupted, the corruption will be found in the first 64 bytes. Therefore, fragment-free checks the first 64 bytes of the frame for damage. If no problems are found in the first 64 bytes of the frame, the forwarding process begins!

CCNA Exam:

What command enables the dynamic mappings of DLCIs to IP addresses? Is this command used globally, at the interface level, or elsewhere?

Answer: That's the frame-relay inverse-arp command, and that should be enabled on the appropriate interface and/or subinterfaces. Inverse ARP is enabled by default on Cisco router serial interfaces.

CCNA Security And CCNP / ISCW Exam:

What is RFC 3704 filtering, and why would we use it as part of a security plan?

Answer: IP Spoofing can be used against your network in several ways:

To inject a stream of malicious code and/or commands into your network

To trick legitimate network hosts into sending sensitive data to the attacker

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