QOS on point to multipoint

Unanswered Question
Aug 18th, 2008

I need some assistance in setting up QOS on a point to multipoint MPLS link. Unfortunately, I don't have much experience with point to multipoint connections. We have a 25Mbps MPLS connection at our main data center. We have about 22 offices connected through T1s on the same MPLS network. I have written a service policy to apply to the T1 serial interfaces at each office to guarantee bandwidth for voice. However, I'm not sure how to approach it on the 25Mbps connection. I need to guaranteed bandwidth for voice to each destination on a T1. Any recommendations?



I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3 (4 ratings)
tdrais Mon, 08/18/2008 - 10:17

First is to call your MPLS provider and see how and if they support QoS.

You issue is not so much outbound which you can control it is inbound from the MPLS provider.

If your all hub and spoke then it may be possible without the provider but if its 'any to any' then the MPLS provider will need to do the QoS for you.

For example say you have 3 sites all with a single line. Both sites 2 and 3 are sending data to site 1. Sites 2 and 3 have no idea about each other so they will send to max line rate. Now of course this will not fit into the line to site 1 but neither site 2 or site 3 can tell this because all they see is the router in the provider cloud. The only router that can do QoS is the provider router as it sends the data to site1. So to run QoS your provider must do all work. This is one of the reasons I dislike MPLS. All will depend on how good your provider is.

lreadshaw Mon, 08/18/2008 - 11:21

Thank you for the reply. Our WAN setup is purely hub and spoke. There is no any-to-any.

The traffic that I am most worried about is the traffic going from the central site with the 25Mbps connection to the remote offices on the T1s. I want to make sure that, say, a large data transfer to an individual site from the central data center isn't interfering with the voice traffic going to that site. I just don't know how to apply a policy that says "of the 1.5Mbps you are sending to the T1 site, make sure X percentage is available for voice." I know how to do that on a point-to-point T1, but not when 1 side is connected to multiple sites.

Joseph W. Doherty Mon, 08/18/2008 - 17:24

As Tim noted, you still might check with your MPLS provider and determine whether they support a QoS model or provide one for your selection. Often, you would then only need to do is mark the traffic for MPLS egress.

Otherwise, what you might do is configure a CBWFQ policy with one class per remote site, each site's class having a shaper for the far side's egress bandwidth. A child policy could be used to place VoIP into LLQ, etc.

lreadshaw Tue, 08/19/2008 - 14:02

I understood most of that :)

The only thing I'm not clear on is marking the traffic for MPLS egress. How do I do that?


Joseph W. Doherty Tue, 08/19/2008 - 14:20

You can use a CBWFQ policy, on either ingress from your LAN(s) or egress to to your MPLS WAN, to set DSCP values.


(NB: syntax might be incorrect)

class-map LowPriority

match protocol FTP

policy-map MarkTraffic

class LowPriority

set DSCP AF11

class class-default


interface FastEthernet 0

service-policy input MarkTraffic


This Discussion