Will unmanaged switch drop VLAN frames?

I've read differing opinions on this, so I would like to hear from others.  

If I have a Cisco managed switch, and it is plugged into a Netgear unmanaged switch, does the Netgear strip all information permanently from the ethernet frame that it received from the Cisco before sending it on it's way, or does it just drop the frame altogether?
B1izzardAsked:
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Don JohnstonInstructorCommented:
Not enough information to accurately answer.

Is the frame coming from the Cisco an ISL, 802.1q or just a plain ethernet frame?

If the frame is an ISL frame, and the encapsulated packet is larger than 1470 bytes, then the Netgear switch will most likely drop it. If the packet is smaller than 1470 bytes, then it will pass.

If the frame is an 802.1q frame, and the encapsulated packet is larger than 1496 bytes, then it's possible the Netgear switch will forward the frame. But it depends on whether the switch supports "baby giant" frames. If the packet is smaller than 1496, then the frame will be forwarded.

If the frame is a plain ethernet frame, then it will be forwarded.


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luc_roySystem AdminCommented:
You will get whatever data is on the access port and the rest will be dropped.

Some new smart switches can do an additional vlan but it's still one Vlan per port and all else are dropped.
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from_expCommented:
If unmanaged switch is capable of transmitting frames of 1514 size, then vlans will flow through that switch.
however, I would not recommend using unmanaged switches with vlans.
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B1izzardAuthor Commented:
Had to do a little research to find out how how you got the 1470 and 1496 numbers, but now I understand why this can be a little more complicated than a simple yes or no answer.  Since you probably all know this, I will post it for others.  Please correct if any of this is wrong, as I pulled it off the internet.

Ethernet has a maximum frame size of 1500 bytes, so most devices use 1500 as their default MTU. An Ethernet packet larger than 1500 bytes is called a Jumbo Frame.   802.1q max frame size is 1522.
ISL max frame is 1548 bytes
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Don JohnstonInstructorCommented:
Close, but not quite. :-)

Ethernet has a maximum FRAME size of 1518 bytes. The PACKET inside of the frame is limited to 1500 bytes to avoid exceeding the max ethernet frame size.  A packet is encapsulated in a frame that has a 6 byte destination address, 6 byte source address, 2 byte type and 4 byte frame check sequence added.

So other than interchanging "Frame" and "Packet", it sounds like you've got it.
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B1izzardAuthor Commented:
So basically the unmanaged switch will drop it if the VLAN packet size is greater than what it can handle, and this varies by manufacturer.  Thanks for clearing that up.  
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