Suppose you connect a trunk port from a VLAN capable network switch to a (VLAN incapable) consumer-grade network switch via a direct cable. Now the former switch send the later switch a 802.1Q-tagged Ethernet frame. What should the later switch do? Drop the frame? Forward the frame? Undefined behavior?
If the behavior is undefined, what is most probable?
Edit: Thank you for your answers. To summarize, the behavior of the consumer switch depends on:
- How it handles frames with
0x8100in the EtherType field1
- How it handles jumbo frames, or frames with payload larger than 1500 bytes
Wikipedia has a nice diagram comparing an untagged and a tagged Ethernet frame:
There are reports that some consumer-grade switches pass VLAN-tagged frames just fine.
1 or more precisely, where an EtherType field is expected for non-tagged frames