I was asked to review a network architecture at work. As I am not very familiar with VLAN utilization with multicast, that is why I am here to request your help.

The old network consists of many servers linked to clients though a switch (can be seen as separated networks).

Each client have very specific needs like a dedicated DHCP configuration, video broadcast through multicast, .... I can't put them on the same network even if I review services configuration for example.

We want to limit the number of server used, and put them in the same room, and later virtualize them.

The use of VLAN seems mandatory, to separate those network, but as most servers use multicast for the video, i don't want to have to broadcast the video stream on each server.

They use a lot of network and CPU ressources, which isn't optimal for the future.

I can't use IGMP on client to retrieve the media stream, and VLAN must be untagged for clients as those both features are not supported.

Clients won't answer to the video stream, they will just receive it, and display it.

My initial idea was to set a separate VLAN on which the video stream will be send, and then put it on the untagged port of the switch linked to the client (with the video stream also untagged).

Is that possible? Add an unidirectional untagged VLAN into another untagged VLAN? Which kind of switch could handle that kind of thing?

I am aware that I could solve this problem using a router, but i can't do it on some clients, as they use very specific kind of traffic (Ethernet broadcast) to work.

Thanks for reading this long post, and sorry for my english, i am not a native speaker.

I hope someone got some ideas or pointer to solve my problem.

Here is a small Scheme :

<server1>      <=== VLAN UNTAGGED1 ===>    <          > <==VLAN UNTAGGED1+3 ==> Client1

<server2>      <=== VLAN UNTAGGED2 ===>    <  switch  >

<video server> <=== VLAN UNTAGGED3 ===>    <          > <==VLAN UNTAGGED2+3 ==> Client2
  • If the clients aren't send igmp joins how for the client get the multicast stream? Dec 12, 2014 at 5:04
  • The multicast stream work like broadcast, every client receive the stream on their network interfaces, and then proceed to display it on the screen. It can be consider as a broadcast distribution (every port of the network receive it), but it is still multicast . Dec 12, 2014 at 8:42
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Aug 11, 2017 at 1:49

2 Answers 2


It seems that the Asymmetric VLAN feature fit my needs.

It is a feature from DLINK switch, it might have another name on other manufacturers.

It is possible with this feature to have two untagged VLAN on a single port, and still keep isolation between VLAN. Here is an example.

Let's say i have a VLAN 2 with a type A of clients, a VLAN3 with a type B of clients.

A & B clients can't coexist on the same network, and both shares a ressources present on VLAN4.

We will be able to spread VLAN4 on the port of client A and client B, but client A and B won't be linked with each others, even with untagged network.

We could consider that VLAN2 and VLAN3 are contained into the VLAN4.

In my case the multicast is the shared ressources, and i still keep my client network separated.

Here is a small documentation from Cisco about the feature : http://www.cisco.com/c/en/us/td/docs/switches/connectedgrid/cgs2520/software/release/15_0_2_ed/configuration/guide/cgs_15_0_2ed/cgs_asym-vlan.pdf

Thank you for your time.

  • Sorry, i made an edit, i hope it is clear enough. I don't have the switch yet, so i can't give information on how to configure it on the switch. Dec 12, 2014 at 15:05

I know that the Cisco SG300-28 can do the thing you want with sending multiple untagged vlans out an interface, as i have seen that in production.

Have you thought about sending the multicast stream out and then configure the switch to statically join the multicast stream on ports where it is necessary. That would atleast be my prefered way of getting arround this issue.

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