2.1 Describe and verify switching concepts

2.1.a MAC learning and aging

Mac addresses are learned on the port based on received packets. The default aging for Cisco switched is 5 mins (300s).

See this topology:

 

Screenshot_2018-04-21_19-28-25.png

Switch#show mac address-table 
 Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
 1 0050.7966.6802 DYNAMIC Et0/2
 1 0050.7966.6803 DYNAMIC Et0/3
Total Mac Addresses for this criterion: 2

After issuing pings (10.0.0.1 – .4):

Switch#show mac address-table 
 Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
 1 0050.7966.6800 DYNAMIC Et0/0
 1 0050.7966.6801 DYNAMIC Et0/1
 1 0050.7966.6802 DYNAMIC Et0/2
 1 0050.7966.6803 DYNAMIC Et0/3
Total Mac Addresses for this criterion: 4

2.1.b Frame switching

The switches consult the mac-address table when making switching decisions on individual frames.
If there is no match for the destination frame, the switch floods the frame out all ports.

2.1.c Frame flooding

If there is no match for the destination frame, the switch floods the frame out all ports.

Here is an example, at the beginning of this exercise the switch’s mac-address table is empty. PC1 attempts to ping PC4.

The switch floods the ARP frame to all ports to the layer 2 broadcast address(FF:FF:FF:FF:FF:FF):

Screenshot_2018-04-21_20-01-37.png

Screenshot_2018-04-21_20-01-46

Here you can see the before and after on the switches mac address table:

Screenshot_2018-04-21_20-00-48.png
2.1.d MAC address table

The mac address table records the mac address for devices attached to each port.

Switch#show mac address-table 
 Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
 1 0050.7966.6800 DYNAMIC Et0/0
 1 0050.7966.6801 DYNAMIC Et0/1
 1 0050.7966.6802 DYNAMIC Et0/2
 1 0050.7966.6803 DYNAMIC Et0/3
Total Mac Addresses for this criterion: 4
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