QoS on 6Mbps WAN link

[JeremyTurlin_2]

I hope this is the right spot for this. 

I've got a router with its fastethernet connection going to a device that combines 4 T1s, for a total of 6mbps.  I want to configure a QOS policy on the Fastethernet interface to prioritize user traffic over backup traffic.  My plan was to use PQ to set the top priority as user traffic and the lowest as backup.  The problem is I don't know if PQ will recognize the bandwidth statement on the interface configuration or if it will simply see fastethernet and use 100mbps as the limit for congestion management.

I want to put bandwidth 6000 on the interface config and have PQ use that as its congestion point.  Will this work?

I may be thinking through this incorrectly.  If I assign user traffic, via an ACL, to priority 1 queue will it always be sent first?

something like:

access-list 10 deny <bandwidth traffic>

access-list 10 permit ip any any  (the rest is considered user traffic)

priority-list 1 protocol ip high list 10

interface fa0/0

priority-group 1

Would this accomplish my goal of letting backup traffic use whatever bandwidth is available until user traffic comes along?

[Calin C.]

Hello,

I would recommend to use MQC rather than legacy QoS.

What I would do is the following.

On the inbound I would match the interesting traffic in ACL and set the correct DSCP values (e.g. EF for PQ traffic)

On the outbound interface

1. Use classes to match the traffic based on their DSCP values

2. Use the classes in the policy-map setting one class for PQ and the rest for CBWFQ

3. Use the policy-map out on the outbound traffic.

In this way you don't only ensure that you prioritize your traffic at your exit point, but also if the upstream providers care about the QoS values their will prioritize your traffic. Any provider with minimum QoS will prioritize the packets market with EF for example.

If you prioritize only at your interface without marking the traffic, indeed your prioritized packets will leave first the interface queue, but you have no warranty that the provider will do the same.

Let me know what you think about my proposal.

Calin

[Joseph W. Doherty]

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Posting

I believe PQ only reacts to interface congestion.  If you want to properly prioritize for 6 Mbps later downstream, you need a hierarchal policy with a shaper.  Something like (syntax might be incorrect):

policy-map parent

class class-default

shape average 6000000

service-policy child

policy-map child

class backup

bandwidth 8000

interface f0/0

service-policy parent out