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QID:SW100
#1
The answer and explanation to QID:SW100 blow my mind regarding anything I?ve learned to this point with the operation of VLANs.  Here is the question:

Both host stations are part of the same subnet but are in different VLANs.  On the basis of the information presented in the exhibit, which statement is true about an attempt to ping from host to host?

Exhibit:

Hostname SW1
!
Interface Gi0/1
Switchport mode access
Switchport access vlan 2
!
Interface Fa0/1
Switchport mode access
Switchport access vlan 2


Hostname SW2
!
interface Gi0/1
switchport mode access
switchport access vlan 5
!
Interface Fa0/1
Switchport mode access
Switchport access vlan 5

The topology indicates Host-1 with IP of 10.10.10.1/24 hanging from fa0/1 from SW1.
Host-2 with IP of 10.10.10.25/24 hanging from fa0/1 from SW2.  SW1 & SW2 both Gi0/1 ports are connected via a common link.


[] A trunk port will need to be configured on the link between SW1 and SW2 for the ping command to be successful.

[] A Layer 3 device is needed for the ping command to be successful.

[] The ping command will be successful without any further configuration changes.

[] The two different hosts will need to be in the same VLAN in order for the ping command to be successful.

Correct Answer: The ping command will be successful without any further configuration changes.

Explanation: On each switch, both ports Fa0/1 and Gi0/1 are configured as access ports and in the same VLAN.  Since no VLAN tagging is used in the frames sent to an access port, therefore, the traffic received on port Fa0/1 is sent untagged to port Gi0/1, that resides in the same VLAN, and vice versa.

For example, when Host-1 sends traffic destined for Host-2, switch SW1 simply forwards frames out Gi0/1 without any VLAN tagging.  Switch SW2 treats it as normal Layer 2 traffic received on access port in VLAN 5.  Since Fa0/1 also resides in VLAN 5, the switch will forward it out Fa0/1 without any restriction.

:o Say what???  I?ve always understood that any inter-VLAN traffic requires a Layer 3 device ? be it a router-on-a-stick, multi-layer switch, layer 3 switch, regular router?what have you.  But this business about two switches being configured as Layer 2 devices and crossing VLANs is quite baffling.
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#2
This is a very confusing question.  But I think it has something to do with the traffic being untagged.
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#3
I first thought it wouldn't ping. Set it up in packet tracer or on equipment. It pings!!!
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#4
Testing is the best way to find out.  Good job.
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