weird question: dot1q and hub

I know this is a weird question, but someone asked me and I thought I'd throw it out. I have no intention of implimenting it to see, but it started me thinking.

A client wanted to know if he could run a dot1q trunk through a hub. Basically two cisco switches, trunked together but somewhere between them a hub.

Will the hub break the trunk. I know you'll get a lot of stuff happening at the hub, but will the two switches actually trunk if the hub is there?

Reply to
thcollicutt
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I would think this would work, however this is obviously not a smart thing to do. All ports (on the hub) would see that traffic, but as long as the endpoints are tagging the frames properly, I don't see why this would not work. The hub should not be 'manipulating' the frames at all, so I'd be interesting to see the results. If you do try, let me know how you fare.

Reply to
Trendkill

From a hub point of view the only difference from a standard frame and a .1q frame is the payload size, wich in .1q frames could be 4 bytes greater, as ong as the hub doesn't discard these trames your setup is going to work, although not a good practice. Bye,

Reply to
Tosh

Obviously bad practice, but yes the hub (or an unmanaged switch) will allow tagged packets to "pass through". Any other hosts connected to the hub/unmanaged switch will be belong to the native vlan of the trunk.

Reply to
wayne

I doubt the hub will allow the dot1q packets because the extra 4 bytes on the packet will be seen as an "overrun" and the hub should discard the packet. You can try it and it might work, but as the previous poster said this would be very bad practice.

Reply to
Thrill5

Said that we all agree on the bad practice, generally todays ethernet interfaces are built to manage longer frames than the original 1518 bytes limit, never tried with hubs, but I successfuly tried to transparently pass trunks through media converters, unmanaged switches and even low end wireless bridges. Bye, Tosh.

Reply to
Tosh

Hubs aren't sufficiently intelligent for detecting overruns and discarding packets. They are just multiport repeaters which blindly pass on the signals between their ports. The only thing a hub is able to detect is a collision.

Now if the "hub" was really an unmanaged switch that would be a different story ...

Reply to
Tilman Schmidt

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