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QoS on Fast-Ethernet interface connected to ISP DSL router

Michael Huffman

I have a hub and spoke DMVPN setup.

Each remote site has a Cisco 1861 router (latest IOS) with it's fa0/0 interface connected to an ISP supplied DSL router that is doing all the authentication for me and bridging. No QoS of any kind on the ISP router.

The DSL has an 800kbps upload limit.

Here is my question.

I'm running VOIP across all these tunnels and want to implement QoS. I can run AutoQoS on the internet facing fa0/0 interface but it would seem to me to be pointless as the interface is running at 100Mbps and the DSL is only 800kbps. The calculations AutoQoS would make would be based on the interface speed, not the DSL

My thought would be to use traffic shaping on the default-class to limit it to actual bandwidth of the ADSL (or should I make it less ?) for non VOIP traffic.

Relevant config:

class-map match-any AutoQoS-VoIP-RTP-Trust
match ip dscp ef

class-map match-any AutoQoS-VoIP-Control-Trust
match ip dscp cs3
match ip dscp af31

policy-map AutoQoS-Policy-Trust
class AutoQoS-VoIP-RTP-Trust
  priority percent 70
class AutoQoS-VoIP-Control-Trust
  bandwidth percent 5
class class-default
  shape average 800000       << Shape class-default to 800kbps >>

interface FastEthernet0/0
description Outside
ip address x.x.x.x
ip nat outside
ip virtual-reassembly in
zone-member security out-zone
duplex auto
speed auto
auto qos voip trust
service-policy output AutoQoS-Policy-Trust

Any other ideas or would this do the job ?

3 Replies 3


Hi Michael

I feel you are better off with allocating the remaning bandwidth the class-default, also make sure that you define the exact available bandwidth on the wan interface using bandwidth command. If you dont use this command to define and leave it as it then you will end up reserving 70% of available bandwidth as mentioned on the interface by default which is 100Mbps in your case. Change the bandwidth statement under the interface first and also make sure that you allocate only 75% of the available bandwidth to the QoS clasess since the rest is required for other keepalives/routing updates etc., I think you are bettter off with this allocation or else you need to make sure that you reserve 100% bandwidth on the interface and also you need to make sure that you define a class for routing and reserve 3 to 5 % of the total bandwidth for that class.


Adrian Lazar

Hi Michael,

I think it would be better for you to use nested policy-maps.

The first policy-map should be a shaper that shapes all traffic to 800 kbps. This policy-map should have only one class, class-default, the shaper configured under that class and the second policy applied to it.

The second policy-map is the queueing policy which may look like your policy AutoQos-Policy-Trust but without the shaper in class-default. Of course it is essential to define the bandwidth under the interface in order for the percent commands to apply to the right value.

Best regards,


Michael Huffman

Thanks. I wasn't clear on whether the bandwidth statement was part of this. I knew it would be used as part of the dynamic routing calculations, but it makes sense that the QoS would use it as well.

I'll give this a shot and thanks again for the input !

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