I've inherited a network with approximately 200 computers and no VLANs configured. We are currently adding a system that uses multicasting to communicate with each other and will be adding VoIP in 2 years. I'd like to set up VLANs, with which I had some experience 10 years ago, but I'm a bit rusty, and I need my memory cells re-awakened.

The network address is I was thinking to set up a VLAN and subnet for the multicasting (6 devices) and use, but is the subnetting necessary or is the VLAN sufficient? In the past I did both subnetting and VLANs.

My second question is: does the router need to be configured with VLANs to support any of this? It's of course set up for the network but management of the router is contracted out and I can't make any changes myself. Requests for changes take months so I'm hoping that I don't need to request a change or I'll need to request plans for future configurations as well. I'd rather not have to deal with them. QoS is already configured so that's covered for the VoIP at least.

  • I'll let others comment on the VoIP aspect, but a separate VLAN for your multicast application isn't necessary. – John Jensen Oct 30 '15 at 14:16
  • 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 can provide your own answer and accept it. – Ron Maupin Aug 7 '17 at 1:25
  • Sorry but I don't see how or where to "accept" an answer............ – Wendy Aug 9 '17 at 14:35
  • It is the Check to the left of an answer. – Ron Maupin Aug 12 '17 at 20:29

One of primary reasons for segregating devices into separate VLANs is so that you can treat traffic from the VLANs differently, for example by applying a security policy, or a QoS policy.

You don't mention how your 200 users are connected (one big switch or several small ones?), but for VoIP, you might want to to put your phones in a separate VLAN so that you can apply a QoS policy on your switches. OTOH, depending on the kind(s) of switches, you may be able to do that with just DSCP or CoS markings.

You say QoS is already configured, but I'd like to know exactly how before making any additional recommendations.

And I agree with @RonMaupin and @JohnJensen that there probably isn't any justification for putting your multicast devices in a separate VLAN, unless you intend to treat that traffic differently.

| improve this answer | |
  • Thanks Ron, The 200 users are spread out among 15 buildings with fiber between buildings & HP smart, dynamic layer 3 switches in each. I don't know how the QoS is configured, they won't even call it that, they call it Gold Car, maybe that's a legit name but I've not heard it before. They aren't contracted to manage the LAN. I don't have alot of faith in them because it takes so long to get requests implemented & they shipped us a new router which when installed had to be completely reconfigured leaving us down for 1.5 hours. Frustrating but hands are tied. Thanks again! – Wendy Oct 30 '15 at 20:35
  • @Wendy, if the users are truly separated with layer-3 devices as you say, they are not all on the same VLAN since a VLAN is halted by a layer-3 boundary. Also, multicast, unless you configure the layer-3 devices for multicast routing, can't cross a layer-3 boundary. Layer-3 switches, if actually doing the layer-3 part, are really routers, too. – Ron Maupin Oct 30 '15 at 20:53
  • @Wendy, Gold CAR probably refers to the carrier charging you for honoring your QoS markings. That's what Verizon Business calls it. It doesn't automatically confer QoS on your traffic, you still need to set up the marking, shaping, queuing, policing, RED, etc. for QoS at your sites. It sounds like you are paying for something which you don't use, yet, but you should have it to work with your QoS configurations when you add VoIP. – Ron Maupin Oct 30 '15 at 21:48

First, the proposed subnet, is within the existing subnet, You will need to pick a subnet outside the range of the existing subnet.

I'm not sure why you would actually need a separate subnet for the multicasting, but a separate VLAN and subnet for VoIP is probably the way to go since you don't really want all the broadcast traffic for the users impeding your VoIP traffic. Separating the traffic at layer-2 with a separate VLAN is probably the way to go.

You will definitely need router changes. The router needs to know about any new subnets, and the QoS will need to be modified for any new VLANs and subnets.

I'm almost tempted to call this question off-topic since you don't really have the control of the network necessary to make the network changes required to accomplish your plan.

| improve this answer | |
  • Thanks Ron, No vlan for the multicasting then. I couldn't remember if vlans had to be configured in the router even if a different subnet wasn't created. I've been away from the networking world for a few years and forgotten a few things. BTW I do have some control, I just have to make the requests and wait. I'm not allowed to do them myself unfortunately. – Wendy Oct 30 '15 at 15:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.