Testing QoS over MPLS

Posted on 2011-05-11
Last Modified: 2012-06-22
Greetings -

How would one confirm that QoS is working over a MPLS VPN link between sites?

Here's the situation.   We have two offices, let's call them Corp and Remote.   At the Corp site sits a Phone System.  The handsets connect to the Phone System over IP.  Corp and Remote are connected by a MPLS VPN link.   The MPLS VPN is managed by our service provider.  When the link was established, I requested specific ports to be granted high priority when traveling bidirectionally between offices.

Users at the Remote site are now complaining about call quality issues.  I suspect this is due to saturation on the link or that the QoS is no longer properly configured.

Are there tools available that will let me confirm QoS from one end to the other? I have a conceptual understanding of advanced networking, but am by no means an expert so a little detailed information may be required.

Thank you for your responses

Question by:silsuba
    LVL 3

    Accepted Solution

    There some things you can do.

    I would test the Mean Opinion Score (MOS) of the links with VoIP software.  Something like ManageEngine OpManager has a VoIP testing component and it is relatively easy to setup and configure.  This will give you insight just on the quality of the MPLS link without any protocol overhead.

    If you are using Cisco Routers as the endpoints with QoS configured, you can issue some commands to see if QoS is affecting the traffic. Issuing a 'show policy-map interface <interface name of port facing carrier> output' and a 'show policy-map interface <interface of port facing carrier> input'

    <interface of port facing carrier> = something like GigabitEthernet0/0

    If you are doing a vpn tunnel through the carrier network, you may need to preserve the markings in the packet.  When the original packet goes through the vpn tunnel, it is being encapsulated and the QoS information is being ignored.  You should be able to issue a 'qos pre-classify' command and it will retain the QoS marking throughout the network.  This applis to GRE and tunnel interfaces on a Cisco router.  I am not sure how this will work on other equipment.

    Also, without knowing your environment, it is a little hard to narrow down what direction you should be pointed.  If you could upload a copy of the configurations on the routers, that would be helpful.

    Hope this helps.

    Author Comment


    Thank you for your comments.   It does help greatly in that I realized I need to add additional information to my post.   The link between sites is fully managed by the service provider, so I have no access to the routers or thier configurations.

    I will take a look at what you recommend in the first paragraph of your response.  This feels like the tool I may be looking for.

    LVL 26

    Assisted Solution

    If the routers are fully managed by the ISP, the only thing you can do isnegotiate with them on what level COS they are marking your traffic entering their MPLS network.
    LVL 17

    Assisted Solution

    Since the link is fully managed by the SP, it is up to them to look at the router statistics.

    Ask them to check if what you defined as higher priority is getting enough bandwidth. Possibly they gave your VoIP traffic higher priority, but only up to (say) 50% of the total traffic.

    They need to give you traffic statistics, so you can check if any other traffic is sneaking in to the high priority traffic.

    Author Closing Comment

    All good information and exactly what I need to know.  I had thought the burden would fall on the ISP but needed confirmation

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