VoIP over MPLS

[h382]

New to cisco here..

I have 2 offices connected via an existing MPLS network. There are 2800 Series Routers at both sites, and 3650 Switches at both sites. The Avaya PBX was connected via P2P T1's but are now being moved onto the MPLS network.

The Avaya Gateways are on the same network as the rest of the office at both sites. I have 3 gateways that will be plugged into the switch at each site. How would I need to configure the switches and routers to ensure QoS between locations?

 

[VinceWhirlwind]

You will need to implement VLANs on your 3650's and 2800s.

You will need to configure the switches and routers to trust and honour QoS tagging OR to assign QoS tagging based on access lists.

You will need to test that your MPLS provider honours the tagging through their network by viewing packets incoming to each site have tags on them same as they had when they were sent (some MPLS providers strip the tagging if you don't check).

 

[h382]

Do the gateways need to be on separate subnets from the rest of the office at each location to utilize VLANs?

I tried setting up a separate VLAN last week, but ran into issues with connectivity. The data is all on default VLAN 1 currently. I tried creating a VLAN 5 for voice, but I don't know if I was even running the proper commands.

 

[VinceWhirlwind]

The voice should all be on its own subnet, separate from the data.

"VLAN" is synonymous with "subnet" in good design - you have one subnet per VLAN.

Setting up VLANs isn't something you'll figure out in ten minutes - you will need to do a bit of research and testing.

And you can't just wade in and start configuring your devices - you need to come up with a design first.

The basic steps are:
- choose where you are doing your inter-VLAN routing: switches or routers (one per site, assuming you have a different subnet on each site).
- create the VLAN with an IP-addressed VLAN interface on that device (this is the default GW for that subnet)
- create the new VLAN no any device where it will be used
- configure the network links as trunks, carrying both VLANs, wherever both VLANs need to cross a link
- configure edge ports in the appropriate VLANs for the device they support.

 

[Quadratic]

A few things:

First, in ANY scenario like this, it is worth asking your MPLS service provider what their QoS strategy is. Usually it would be a premium service, but if you want to prioritize your voice traffic through the MPLS cloud that is a possibility.

Second, for QoS marking/tagging, decide what type of markings you are going to use. Typically when connecting to an MPLS provider, you should be using layer 3 markings (IP Precidence, DSCP), but make sure to check what types of markings are preserved by their network and which aren't (CoS Ethernet markings are another option though likely will not be preserved by the provider).

Third, while NOT a technical requirement, in most cases and especially in this case with a converged voice/data network, yes you should have a one-to-one mapping of subnets to vlans, and yes you should isolate voice traffic on a separate subnet/vlan than your data traffic. If done that way, your classification can be as simple as an access list defined in a class-map, with a policy-map giving priority in some fashion to voice over data.

Fourth, once traffic is identified as voice, you should treat it differently. I can speak in generalities at this point but it really depends on your traffic profiles and the configurable options available to you. Voice is typically more important than video, which is more important than voice signalling, which is more important than data.

Fifth, there are actually many ways that you can be "connected via an MPLS network". That is an extremely flexible WAN solution, so just from that it's difficult to tell you how you should be approaching QoS. Some MPLS providers are almost completely transparent, doing QnQ tunneling to let you trunk between your switches across the WAN, for example, or you may face the provider with routed interfaces and extend your internal routing protocol into the provider network for end-to-end DSCP-based QoS. Way too many possibilities with the available info.

CCNP, CCDP, CCIP