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MPLS CoS Question - Default traffic keep on overload


Hi guys,

Need some advise from you.My site have a MPLS connection with a CoS service-policy output configure on it. The problem is, my link keep on congested by incoming default traffic! How do I stop this?

My business class CoS is base on IP range, does I need to ask the provider to put this range on their PE output policy? What I know, provider doesn't do this... Please advise. Many thanks.

1 Reply 1

Cisco Employee
Cisco Employee


Queueing is a functionality local to where the bottleneck resides. So the best solution would be that the service provider implements an outbound QoS policy. I would ask the provider, which options exist, as MPLS providers usually also offer QoS at least on the link to the customer.

If the provider does not offer assistance, you can create a hierarchical input policy. You can shape the received traffic to somewhat less than your interface speed and use a child service policy to do the queueing.

Note: this might or might not work depending on your traffic. If you mainly use TCP the flow controls should give you decent results. If you are under a DoS attack, it will not help you.

An example config:

policy-map CBWFQ

class voip

priority percent 50

class Business

bandwidth percent 30

class class-default



policy-map ShapeIn

class class-default

shape average 1900000

service-policy output CBWFQ

interface Serial0

description MPLS connection

service-policy input ShapeIn

The shaper in policy-map ShapeIn acts like a logical interface hardware Q and the idea is to control the throughput to your MPLS connection locally. With TCP this should give you quite decent results, if the shaper is less than the MPLS connection speed (I assumed 2M here). You need to configure less, because of Layer 2 overhead on the wire, which is not seen on input.

In brief:

1) Best: provider implements QoS according to your requirements

2) workaround: hierarchical input policy

Hope this helps! Please use the rating system.

Regards, Martin

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