Chapter 5 - Ethernet LAN Switching

Question 1

LAN Switching Summary

Answer 1

Switches use Layer 2 logic, examining the Ethernet data-link header to choose how to process frames. Switches make decisions to forward and filter frames, learn MAC addresses, and use STP to avoid loops.

Question 2

EXEC Command

show mac address-table

Answer 2

Shows all MAC table entries of all types

Question 3

EXEC Command

show mac address-table dynamic

Answer 3

Shows all dynamically learned MAC table entries

Question 4

EXEC Command

show mac address-table vlan vlan-id

Answer 4

Shows all dynamically learned MAC table entries in the VLAN

Question 5

EXEC Command

show mac address-table dynamic address mac-address

Answer 5

Shows the dynamically learned MAC table entries with the MAC address

Question 6

EXEC Command

show mac address-table dynamic interface interface-id

Answer 6

Shows all dynamically learned MAC table entries associated with that interface

Question 7

EXEC Command

show mac address-table count

Answer 7

Shows the number of entries in the MAC table and the total number of remaining empty slots in the MAC table

Question 8

EXEC Command

show mac address-table table aging-time

Answer 8

Shows the global and per-VLAN aging timeout for inactive MAC table entries

Question 9

EXEC Command

clear mac address-table dynamic

Answer 9

Empties the MAC table of all dynamic entries

Question 10

EXEC Command

show interfaces status

Answer 10

Lists one line per interface on the switch, with basic status and operating information for each

Question 11

EXEC Command

clear mac address-table dynamic [vlan vlan number] [interface interface-id] [address mac-address]

Answer 11

clears (removes) dynamic MAC table entries: either all (with no parameters), or a subset based on VLAN ID, interface ID, or a specific MAC address

Question 12

EXEC Command

mac address-table aging-time [time-in-seconds] [vlan vlan-number]

Question 13

Broadcast Frame

Answer 13

An Ethernet frame sent to destination address FFFF.FFFF.FFFF, meaning that the frame should be delivered to all hosts on that LAN.

Question 14

Known Unicast Frame

Answer 14

An Ethernet frame whose destination MAC address is listed in a switch’s MAC address table, so the switch will forward the frame out the one port associated with that entry in the MAC address table.

Question 15

Spanning Tree Protocol (STP)

Answer 15

A protocol defined by IEEE standard 802. ID. Allows switches and bridges to create a redundant LAN, with the protocol dynamically causing some ports to block traffic, so that the bridge/ switch forwarding logic will not cause frames to loop indefinitely around the LAN.

Question 16

Unknown Unicast Frame

Answer 16

An Ethernet frame whose destination MAC address is not listed in a switch’s MAC address table, so the switch must flood the frame.

Question 17

MAC Address Table

Answer 17

A table of forwarding information held by a Layer 2 switch, built dynamically by listening to incoming frames and used by the switch to match frames to make decisions about where to forward the frame.

Question 18

Forward

Answer 18

To send a frame received in one interface out another interface, toward its ultimate destination.

Question 19

Flood

Answer 19

The result of the LAN switch forwarding process for broadcasts and unknown unicast frames. Switches forward these frames out all interfaces, except the interface in which the frame arrived. Switches also flood multicasts by default, although this behavior can be changed.