VLAN VoIP setup for remote offices

[dgrizzard]

Our company is going to be implementing VoIP(testing at a small office first, only 3 phones, to work out all the kinks with the network and what not) with our nortel pbx. I've heard suggestions on keeping the voip phones on their own VLAN, which at our main office I dont see as a problem, but we wont be using ip phones there so it doesnt matter. All phones will be at remote offices. Currently our setup is a hub/spoke setup for frame-relay. Most of the connections are full/half t1 to our remote offices. Most offices have Cisco 1720 routers, 2950XL switches and the main office has a cisco 2621. My question is can I create 1 big VLAN for all remote offices/main office that I can put all of my IP phones on? And if I can how do I do this(specifics or a great cisco doc on this would be good). Also if I cant do this what would be the best thing to do to get them on VLANs? I'm new to working with VLANs so please treat me like an idiot.

 

[lambent]

If you need to implement VOIP across WAN links, you'll probably need to implement WAN QOS also such as Low Latency Queueing.

Usually we'll create a separate VLAN/subnet within the LAN for the ease of applying ACL/marking traffic/prioritizing traffic...etc.

 

[dgrizzard]

I currently have the router configured for LLQ based on ports that VoIP uses. I would like to set it up based on VLAN/subnet ,but I'm wondering how to setup this separate VLAN/subnet across the whole network(across multiple routers/switches) so its transparent to the user if they move from one office to another.

Thanks in advance

 

[lambent]

hmm I can't think of any solution to carry VLAN tags across FR network.

But I think using a dedicated PVC for the VoIP network and use a point-to-multipoint topology running the same subnet may work tho I didn't try this in real life. However this involves subscribing another PVC and may not be cost-effective.

 

[dgrizzard]

I was thinking then...what if I setup a sub-interface on the ethernet port(since I only have one on each of the 1720 routers) and made it into a different subnet, did this at each office and our main office, and also put the networks in eigrp. Would it give me the same effect as having one big VLAN across the network? As far as: being able to take a VoIP phone that was set for this separate network and move it from office to office and it would still work?

TIA

 

[lambent]

A subnet cannot be divided by layer-3 devices. Just remember the rule of thumb: layer-3 interfaces of a layer-3 devices should belong to different subnets.

If you insist to use same VLAN across your WAN, you can also try to use MetroEthernet.

 

[dgrizzard]

I didnt think it would work; back to the drawing board. By MetroEthernet do you mean something similar to Verizon's TLS(transparent lan service)?

 

[lambent]

You'll have to discuss this with your local ISPs that provide similar service. In my company we have subscribed a 9Mbps MetroEthernet connection to remote offices on a fast ethernet interface and we use subinterfaces and 802.1q to carry different VLANs on the WAN.

Also in this case you may want to use LAN QOS features such as DSCP/TOS to mark voice traffic as critical traffic. However you must make sure that your ISP network allow the forwarding of these DSCP/TOS tags. If these tags are reset in the ISP network, then your QOS will not be working end-to-end.

An MPLS network can provide traffic classification. Again you'll need to ask your ISPs if they provide such service.

 

[dgrizzard]

Verizon is our current frame relay provider, and tags will drop over the frame relay unfortunately. The versions of IOS we're using didnt let me tag it anyway. I think the LLQ via ports will work for now, we are getting the TLS(metroethernet) service at our offices once its available at each office though. It will be nice to have 10mbit or 100mbit service at each office.

 

[megaco]

I have never done it before but maybe MPLS could be used. I'd speak to your ISP as MPLS can be utilised on both datalink technologies.


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