untagged switch- blocker for VLANS or conduit?
I have two scenarios and just curious what happens in each:
first scenario, I have a client on switch A, switch B in the middle, and a destination network on switch C. VLAN 10 is tagged on port 25 and 26 on switch A. the client is connected to 25, and 26 connects to a port on switch B which is untagged on all ports. another port on switch B connects to port 25 on switch C which also tagged for VLAN 10. port 26 on switch C is tagged for VLAN 10 also and connects to the destination network. does switch B block the VLAN traffic? assume the switch is VLAN aware and all ports are untagged for VLAN 10 on switch B.
I’m asking because I have a complex network and I need to add a VLAN to isolate a guest network so the traffic originating in the core of our server room can carry the VLAN directly out to the Internet- the source here is a wireless network. let me know what you think!
first scenario, I have a client on switch A, switch B in the middle, and a destination network on switch C. VLAN 10 is tagged on port 25 and 26 on switch A. the client is connected to 25, and 26 connects to a port on switch B which is untagged on all ports. another port on switch B connects to port 25 on switch C which also tagged for VLAN 10. port 26 on switch C is tagged for VLAN 10 also and connects to the destination network. does switch B block the VLAN traffic? assume the switch is VLAN aware and all ports are untagged for VLAN 10 on switch B.
I’m asking because I have a complex network and I need to add a VLAN to isolate a guest network so the traffic originating in the core of our server room can carry the VLAN directly out to the Internet- the source here is a wireless network. let me know what you think!
The answer is yes... with a caveat.
Tagging adds 4 bytes to the frame. If the original ethernet frame is the max size, then you will have what's called a "baby giant". A frame that is larger than the max size, but only by a few bytes.
If switch B discards frames that are over 1518 bytes, then those frames will be discarded. However, not all switches discard baby giant frames. And on some switches, that behavior is configurable.
Without knowing more about Switch B, it's hard to say with absolute certainty.
Finally, this is the reason why there is a native VLAN. For situations where an intermediate device is not aware of tagging.
Tagging adds 4 bytes to the frame. If the original ethernet frame is the max size, then you will have what's called a "baby giant". A frame that is larger than the max size, but only by a few bytes.
If switch B discards frames that are over 1518 bytes, then those frames will be discarded. However, not all switches discard baby giant frames. And on some switches, that behavior is configurable.
Without knowing more about Switch B, it's hard to say with absolute certainty.
Finally, this is the reason why there is a native VLAN. For situations where an intermediate device is not aware of tagging.
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