Traffic Shaping Question

[shanemoss]

Hi folks,  I'm having some difficulty in understanding traffic shaping configuration I have inherited on an ASR.

The existing configuration is;

interface TenGigE0/0/0/1.10

service-policy output parent-shape-to-nearly-1g

policy-map parent-shape-to-nearly-1g

class class-default

  service-policy child-classify-important

  shape average 900 mbps

!

end-policy-map

policy-map child-classify-important

  class important

  bandwidth 50 mpbs

class-map match-any important

match access-group ipv4 acl-important

end-class-map

ipv4 access-list acl-important

10 permit ipv4 host 1.1.1.1 host 2.2.2.2

20 permit ipv4 host 1.1.1.2 host 2.2.2.2

My understanding is that important traffic should be provided a CIR of 50 Mbps and all traffic outbound from interface TenGigE0/0/0/1.10 should be shaped to 900 Mbps.

Will this existing configuration do this (I suspect it is not working as expected) or should it not be;

policy-map parent-shape-to-nearly-1g

class important

  bandwidth 50 mbps

class class-default

  shape average 900 mbps

Thanks in advance.

[justinhulsman]

Shane,

I haven't ever seen a Two-Tier Policy used like this.  It looks as though the configuration was meant to give the important class 50 Mbps and shape all traffic (both important and default classes) to 900 Mbps.  It would be interesting to see what the output of "show policy-map interface TenGigE0/0/0/1.10" would look like.

-Justin

[Joseph W. Doherty]

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Posting

No, you don't want what you propose, i.e. the CIR traffic not in the child policy.

The original policy is probably okay, although the implicit (child's) class-default should be explicitly defined to use the other 850 Mbps.

[shanemoss]

Thanks for the replies, so what will the following do;

policy-map parent-shape-to-nearly-1g

class important

  bandwidth 50 mbps

class class-default

  shape average 900 mbps

will it give important traffic a CIR of 50Mbps and shape everything else to 900Mbs?  If so, what will the original policy map below do?

policy-map parent-shape-to-nearly-1g

class class-default

  service-policy child-classify-important

  shape average 900 mbps

The reson I suspect there is something wrong with it is that there is an upstream 1Gig port that is carrying this traffic with a lot of outbound drops (the reason for the shaping on this ten gig subinterface was to avoid this) but this may be due to bursts exceeding the averaging shaping?

Thanks again.

[Joseph W. Doherty · Accepted solution]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

Thanks for the replies, so what will the following do;
policy-map parent-shape-to-nearly-1g
class important
  bandwidth 50 mbps
class class-default
  shape average 900 mbps
will it give important traffic a CIR of 50Mbps and shape everything else to 900Mbs?  If so, what will the original policy map below do?

Nope, "important" traffic would be allowed up to full interface bandwidth.  Assuming a 10 gig interface, "important" should be able to obtain a minimum of 9.9 Gbps and a maximum of 10 Gbps.

will it give important traffic a CIR of 50Mbps and shape everything else to 900Mbs?  If so, what will the original policy map below do?
policy-map parent-shape-to-nearly-1g
class class-default
  service-policy child-classify-important
  shape average 900 mbps

All traffic through that policy would be shaped to 900 Mbps, and "important" traffic will have its own queue which should be able to obtain a minimum of 50 Mbps; maximum would be 900 Mbps.

The reson I suspect there is something wrong with it is that there is an upstream 1Gig port that is carrying this traffic with a lot of outbound drops (the reason for the shaping on this ten gig subinterface was to avoid this) but this may be due to bursts exceeding the averaging shaping?

Yes, bursting is one consideration.  Adjusting the Tc down will mitigate that.

Another consideration, I believe many shapers only "measure" L3 and don't account for L2 bandwidth which an interface does.  L2 overhead percentage varies based on packet's size.  If there are many small packets, 10% might be an insufficient allowance.

PS:

The downstream gig interface cannot "see" traffic from any source but this upstream 10g interface?

[shanemoss]

Thanks Joseph, your reply was very helpful in clarifying this for me.  Regarding the upstream 1G interface, yes it will only "see" traffic that has been forwarded by this subinterface.