Cisco CCNA mock exam questions sample test – Question 443

.Based on the output of the show mac-address-table command shown below, where will the switch that produced this output send a frame with a destination MAC address of
ffff.ffff.ffff?

Vlan Mac address Type Ports

1 000f.e544.c2b3 dynamic Fa0/10
1 000d.4589.00b8 dynamic Fa0/5
1 00bd.000b.005bb dynamic Fa0/8
1 0001.0d44.bbdb dynamic Fa0/12
1 0014.0bd4.0054 dynamic Fa0/15
1 00bb.224b.0ac5 dynamic Fa0/1

A. to all ports, listed and unlisted, except the originating port
B. to Fa0/10, Fa0/5, Fa0/8, Fa0/12, Fa0/15, and Fa0/1
C. to no ports, since the MAC address isn’t in the table
D. to all ports excluding the ports listed in the table
E. to port Fa0/15


Correct Answer: A

Explanation:
The MAC address ffff.ffff.ffff is called the Layer 2 broadcast address. It will be sent to all ports listed in the table, or known to the switch, as well as to all those unlisted, or not yet
known by the switch. This excludes the originating port only.
It will not send the frame only to the ports listed in the table (Fa0/10, Fa0/5, Fa0/8, Fa0/12, Fa0/15, and Fa0/1). It will also be sent to ports that are as yet unknown by the switch.
It will not prevent the frame from being sent to any ports because the MAC address is not listed. Broadcast addresses are not listed in the MAC address table. These addresses are
only used to send to all hosts.
It will not send the frame to all ports except the ports listed. This would be the switch’s behavior if the address of the frame in question was not a broadcast address and was not listed
in the MAC address table. Until a switch knows where a frame goes, it will send the frame to all ports that are still unknown or unlisted, with the exception of the port on which it
arrived.
It will not send the frame to port Fa0/15 only. If the frame were addressed to 0014.0bd4.0054, the switch would forward the frame to that port only. When a switch receives a unicast
frame with a destination MAC address that is listed in the table, it will only send the frame to that port.
Objective:
LAN Switching Fundamentals
Sub-Objective:
Describe and verify switching concepts
References:
Cisco > Internetworking Technology Handbook > Bridging Basics > Bridging and Switching Basics