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New Member

Is 3560 capable of traffic shaping?

I'm a bit confused with QoS terms. 3560 Datasheet says this:"Asynchronous data flows upstream and downstream from the end station or on the uplink are easily managed using ingress policing and egress shaping."

So when I use policy-maps on the ingress it's traffic policing and when I use the command srr-queue bandwidth limit on the egress it's traffic shaping? Is it really so?

New Member

Re: Is 3560 capable of traffic shaping?

I agree its not clear the shaping only appears to work via a weighting, the inverse of which is the bandwith it will be shaped to. This isn't really satisfactory as the lowest number you can configure in a weighting is 2 the inverse of which is 1/2 = half the bandwith. so how do you set a 10mb link to shape to 6mb? Come on Cisco experts give us a clue.....

New Member

Re: Is 3560 capable of traffic shaping?

I just might be more confused than what I was before ;)

"Come on Cisco experts give us a clue....." Yep waiting for that too.

New Member

Re: Is 3560 capable of traffic shaping?

I had a similar problem: I need to throttle and shape the outbound/egress traffic BEFORE it hits a branch office T1 router. Our ISP provides the T1 with MPLS for our WAN and they want to charge us $$$/month for deploying QoS. Basically I need to give my remote office higher priority for VoIP traffic over all other traffic. After playing with different configs, I finally have a good working setup. Hope this will help others.

The problem is the SRR bandwidth command has a range of 10% to 90% and our ISP router connects at 100Mbps. So the lowest I can limit is 10Mbps (10%). But I need to get much lower... like 1.5Mbps. After reading several postings for ideas, I forced the port speed to 10/Full and then use the SRR commands rate limit my egress port speed and give priority to my voice traffic.

First you must make sure to map your DSCP to one of the four egress queue like so: (auto qos will automatically generate this for you)

mls qos srr-queue output dscp-map queue 1 threshold 3 40 41 42 43 44 45 46 47

Then setup you router port like so:

interface FastEthernet0/23

switchport access vlan 10

speed 10

duplex full

srr-queue bandwidth share 50 10 10 30

srr-queue bandwidth shape 0 0 0 0

srr-queue bandwidth limit 20

queue-set 2

priority-queue out

mls qos trust dscp

spanning-tree portfast

You'll have to play with the "srr-queue bandwidth limit 20" command as it doesn't match exactly. This gives me about 1.5Mbps total traffic limit. More logically, a value of 15% on a 10Mbps link translates to 1.5Mbps, but it actually limits me to about 1.02Mbps. So play with it.

As you can see, I give my voice traffic 50% on queue 1 and the others just 10 10 and 30 for queues 2, 3, and 4. I used share instead of shape because I don't want to drop any traffic. Anyway, this setup works good even when I flood my T1 in both directions. All phone calls are jitter-free.

Anyway, hope this will help others.


Re: Is 3560 capable of traffic shaping?