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3C17204 - vlan "multi to one"

Occasional Advisor

3C17204 - vlan "multi to one"


I have possibility to buy 3C17204 switch and i need to configure it for vlan's.

Vlan mode has to be "multi to one" (in Planet switche's it's called "MTU vlan").

Which means all ports has own vlan but its sharing with one other port (that same for all vlan').

It's like - vlan1 - port 1 and 2, vlan2 - port 1 and 3, vlan3 - port 1 and 3 etc.

I have manual for 3C17204 but i dont see option like that, there is info : "each port may only be a member of one untagged vlan."


PS sorry for my english.


Re: 3C17204 - vlan "multi to one"

Not sure what the Planet function exactly does, but as for the 3com switch, every port of it can be assigned to one untagged VLAN and to a number of tagged VLANs. For example, you can do your config like:

Port 1: VLAN 1 untagged

Port 2: VLAN 1 tagged, VLAN 2 untagged

Port 3: VLAN 1 tagged, VLAN 3 untagged

and so on. Is this what you need?

Bye, marcos

Occasional Advisor

Re: 3C17204 - vlan "multi to one"

No because i want to port 2 and 3 cant see eachother, it should see only port 1.

Its image from planet switch: http://yfrog.com/juftthg

Maybe i explain in example:

At port 1 i attach cable from dhcp server, at rest of the ports are connected computers. All computers working with my dhcp, but when someone connect other dhcp server i.eg. at port 2 rest of ports wont see it.

I know there is a dhcp snooping but price for switch with that option is too high.


Re: 3C17204 - vlan "multi to one"

Just found some information about this "MTU VLAN" topic in a Planet manual. Seems to be something Planet-specific, since the term MTU usually means "Maximum Transmissio Unit" which has nothing to do with the feature you described. Frankly, as far as I get the picture of this "MTU VLAN" thing, it is quite strange, off-standards and the benefit is questionable (someone correct me if I'm wrong). Even newer Planet switches do not seem to implement this function.

If you want to absolutely isolate the ports from each other in a standards-compliant way, you could do this:

  • configure the client's ports to different VLANs (Port 2->VLAN 2, Port 3->VLAN 3 and so on)

  • configure the DHCP server's port as VLAN trunk (VLAN 1 untagged, VLANs 2 to x tagged)

  • configure one virtual interface per VLAN on the server, each interface in another IP subnet. See your NIC driver's documentation for details.

  • make the DHCP server listen on each VLAN interface

  • enable IP forwarding on the server between the client VLANs and the internet/public VLAN

Hope that helps.

Occasional Advisor

Re: 3C17204 - vlan "multi to one"

Its too complicated, not only me will use it. It has to be simple as MTU vlan.

I found something about MTU vlan in planet manual - its ports based vlan .



This message was edited by kamilfn on 2-24-10 @ 3:08 AM