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New Member

Cisco 1841 traffic shaping

We have a 10Mb MPLS line connected to an 1841 router, the interface is set up for 100Mb/full.  I have a shaping policy set up on the interface, however the provider is claiming that we're bursting to over 10Mb of traffic, can someone please verify that this configuration should keep traffic at 9Mb with no bursting?

policy-map parent

class class-default

  shape average 9000000

  service-policy mpls



interface FastEthernet0/0.2

description MPLS ;ome

bandwidth 10000

encapsulation dot1Q 2

ip address *.*.*.* *.*.*.*.*

ip flow ingress

no cdp enable

service-policy output parent



Cisco Employee

Re: Cisco 1841 traffic shaping

Looks correct ... but keep in mind that the way they calculate 10Mbps may be different than what IOS calculates (I believe IOS doesnt include l2 header.

Re: Cisco 1841 traffic shaping


Burst (bc)= TC*Shaping tool

According to formula lets assume your tc is 125ms (for most of the shaping tool) bc=`0.125*9000000 which equals to

1125000 bits.   So even if there is silent period of few ms it will never exceed to shaping rate=9mb which you have configured

You can provide your values to provider and ask how he assume that it is 10mb.

Hope this helps



Cisco Employee

Re: Cisco 1841 traffic shaping

Yeah, my thought was that you may have this subinterface shaping at

9Mbps, and another subinterface at 1Mbps ... potentially going over the

providers rate. I assume though that this is not the case.

Also, keep in mind also that the granularity of the policer that the

provider is using is probably different that that of the IOS shaper. We

saw this alot with some other service providers as well.


New Member

Re: Cisco 1841 traffic shaping

Thanks guys...I don't know what equipment the provider is using (it's not Cisco), but they're doing

layer 2 policing and claiming that we're bursting WAY above 10Mb and they see

large amounts of packets dropped by their policer.  I don't really see how that's possible with this shaper in place, unless there's a misconfiguration on their end.

The reason this is an issue is that we're having sporadic connectivity issues over this line (as in, complete loss of connectivity for 10-20 seconds at a time, 3-4 times a day).

For troubleshooting we changed the interface to 10/Full and the connectivity issues persisted.  Now that the interface is 10Mb anyway which is what we're paying for, they've removed the policer to see if it fixes the problems, if it does then I would think their policer is misconfigured.  I won't know till probably tomorrow.

This is the only sub interface on the router, it's plugged in directly into their device.

New Member

Re: Cisco 1841 traffic shaping

So we haven't had a single problem after the provider removed their policer, so it does seem like a misconfiguration on their router.