QUICK VLAN QUESTION

very quickly, please dont have a go for posting a dumb question

we have 3 switches linked below

A--------B--------C


A has 2 vlans circ and admin
B i have just found out is not even a maaged switch, its a 8 port unmanaged thing (hub)
C only has Circ vlan at present

Q) i need switch C to have admin vlan aswell as circ

if i just tagg the ports correctly on A and C can they route both vlans correctly even though B is just a dumb switch?

switch B only "needs" circ ports, which it seems to have picked up by default.

replaced switch B is not an option.
removing switch B is not an option.
removing switch B to piggey back off A or C is not an option

The ports on B would have to be tagged to pass on multi VLAN traffic.

Really depends on what B does with the VLAN tags and whether it strips them out. If it doesn't it 'may' work, but unlikely, only one way to tell, set it up and see what happens ;-)

There is a potential problem with large ethernet frames.

The maximum size of a standard ethernet frame is 1518 bytes and switch B will be designed to pass frames of at least this size. VLAN tagging adds an additional 4 bytes to each frame making 1522 bytes per frame. If switch B can handle frames of this size they will pass straight through complete with VLAN tags, otherwise they will be dropped.

You need to make sure that switch B can handle 1522 byte ethernet frames.