Refer to the exhibit. Which VLANs are permitted to send frames out port FastEthernet0/1?
A. 100 – 200
B. 4 – 100
C. 1 and 4 – 100
D. 3 and 4 – 100
Which VLANs are permitted to send frames out port FastEthernet0/1?
Refer to the exhibit. Which VLANs are permitted to send frames out port FastEthernet0/1?
A. 100 – 200
B. 4 – 100
C. 1 and 4 – 100
D. 3 and 4 – 100
Correct answer is definitely B
The correct answer is B. There are a lot of people talking about this in chat rooms who have no idea what they are talking about.
Setting a native Vlan is all about how to treat packets sent by, or received by that switch port. Native Vlans are PORT specific, and can be different from one port to another port on the same switch. Setting a native Vlan just tells the switch “for packets which don’t have a VLan ID in the 802.1q header, insert this Vlan ID into that place in the header” Setting a native Vlan does not permit, block, allow or in any other way permit or restrict a packet. It just fills in the blank, if the Vlan tag is blank. Packets on the default Vlan, Vlan1, will have a “1” in the 802.1q header, so they won’t be “untagged”. Only packets which have no Vlan ID in the header are affected by setting the native Vlan.
Setting native Vlan on a trunk port does two things. I causes incoming packets without a tag to be tagged with the native VLan tag, AND it causes traffic which is being transmitted by that switch port, if the traffic is coming from the native Vlan, to have the Vlan ID STRIPPED, before the packet is transmitted. So that the packet is transmitted WITHOUT an 802.1q Vlan ID.
If you specify 1 or more Vlans that are allowed on a trunked interface then ONLY those Vlans you have included in your allowed list are permitted IN or OUT on that trunk. The switch doesn’t care what Vlan is the native Vlan, if it’s not in the permit list, then you can’t send traffic in or out of that switch port on any VLan which is not permitted.
That said the “switchport trunk allowed vlan” command is optional, and if you don’t use it, then ALL vlans defined on the switch are permitted.
The correct answer is B
I agree on B at least for recent switches. However I remember that in the past (maybe on 2924 or on 2950 switches… or maybe just for a bug of some specific IOS), I had issues because the native vlan was always permitted.