Chapter 7 - Analyzing Ethernet LAN Switching Flashcards
Which of the following statements describes part of the process of how a switch decides to forward a frame destined for a known unicast MAC address?
a. It compares the unicast destination address to the bridging, or MAC address, table.
b. It compares the unicast source address to the bridging, or MAC address, table.
c. It forwards the frame out all interfaces in the same VLAN except for the incoming interface.
d. It compares the destination IP address to the destination MAC address.
e. It compares the frame’s incoming interface to the source MAC entry in the MAC address table.
A.
A switch compares the destination MAC address to the MAC address table. If a matching entry is found, the switch forwards the frame out the appropriate interface. If no matching entry is found, the switch floods the frame.
Which of the following statements describes part of the process of how a LAN switch decides to forward a frame destined for a broadcast MAC address?
a. It compares the unicast destination address to the bridging, or MAC address, table.
b. It compares the unicast source address to the bridging, or MAC address, table.
c. It forwards the frame out all interfaces in the same VLAN except for the incoming interface.
d. It compares the destination IP address to the destination MAC address.
e. It compares the frame’s incoming interface to the source MAC entry in the MAC address table.
C.
A switch floods broadcast frames, multicast frames (if no multicast optimizations are enabled), and unknown unicast destination frames (frames whose destination MAC address is not in the MAC address table).
Which of the following statements best describes what a switch does with a frame destined for an unknown unicast address?
a. It forwards out all interfaces in the same VLAN except for the incoming interface.
b. It forwards the frame out the one interface identified by the matching entry in
the MAC address table.
c. It compares the destination IP address to the destination MAC address.
d. It compares the frame’s incoming interface to the source MAC entry in the MAC
address table.
A.
A switch floods broadcast frames, multicast frames (if no multicast optimizations are enabled), and unknown unicast destination frames (frames whose destination MAC address is not in the MAC address table).
Which of the following comparisons does a switch make when deciding whether a new MAC address should be added to its MAC address table?
a. It compares the unicast destination address to the bridging, or MAC address, table.
b. It compares the unicast source address to the bridging, or MAC address, table.
c. It compares the VLAN ID to the bridging, or MAC address, table.
d. It compares the destination IP address’s ARP cache entry to the bridging, or MAC address, table.
B.
Switches need to learn the location of each MAC address used in the LAN relative to that local switch. When a switch receives a frame, the source MAC identifies the sender. The interface in which the frame arrives identifies the local switch interface closest to that node in the LAN topology.
A Cisco Catalyst switch has 24 10/100 ports, numbered 0/1 through 0/24. Ten PCs connect to the ten lowest numbered port, with those PCs working and sending data over the network. The other ports are not connected to any device. Which of the following answers lists facts displayed by the show interfaces status command?
a. Port Ethernet 0/1 is in a connected state.
b. Port Fast Ethernet 0/11 is in a connected state.
c. Port Fast Ethernet 0/5 is in a connected state.
d. Port Ethernet 0/15 is in a notconnected state.
C.
The show interfaces status command lists one line of output per interface. Cisco Catalyst switches name the type of interface based on the fastest speed of the interface, so 10/100 interfaces would be Fast Ethernet. With a working connection, ports from FastEthernet 0/1 through 0/10 would be listed in a connected state, while the rest would be listed in a notconnected state.
Consider the following output from a Cisco Catalyst switch:
SW1# show mac address-table dynamic
Vlan Mac Address Type Ports
—- ———– ——– —–
1 02AA.AAAA.AAAA DYNAMIC Gi0/1
1 02BB.BBBB.BBBB DYNAMIC Gi0/2
1 02CC.CCCC.CCCC DYNAMIC Gi0/3
Total Mac Addresses for this criterion: 3
Which of the following answers are true about this switch?
a. The output proves that port Gi0/2 connects directly to a device that uses address 02BB.BBBB.BBBB.
b. The switch has learned three MAC addresses since the switch powered on.
c. The three listed MAC addresses were learned based on the destination MAC address of frames forwarded by the switch.
d. 02CC.CCCC.CCCC was learned from the source MAC address of a frame that entered port Gi0/3.
D.
For the correct answer, each entry lists the learned MAC address. By definition, dynamically learned MAC addresses are learned by looking at the source MAC address of received frames. (That fact rules out one of the incorrect answers as well.)
The show mac address-table dynamic command lists the current list of MAC table entries, with three known entries at the point at which the command output was gathered. The counter in the last line of output lists the number of current entries, not the total number of learned MAC addresses since the last reboot. For instance, the switch could have learned other MAC addresses whose entries timed out from the MAC address table.
Finally, the answer that claims that port Gi0/2 connects directly to a device with a particular MAC address may or may not be true. That port could connect to another switch, and another, and so on, with one of those switches connecting to the device that uses the listed MAC address.
