TX Discards

[cisco steps]

what command can allows me to measure the rate of traffic on an interface. The reason I am asking is that I see TX Discards and that is usually indicate more data being transmitted than can be buffered by the interface. I heard that I can use traffic shaping but need some help with it .

Thank you in advance !

[Reza Sharifi]

If you do a "sh interface x/x" it usually shows this command:

reliability 255/255, txload 1/255, rxload 1/255

so, if the interface shows txload 255/255, rxload 255/255 it means the interface is completely saturated. In this case (txload 1/255, rxload 1/255) there isn't much traffic traversing the interface.

HTH

[cisco steps]

Thanks Reza,

I agree with the answer, in My case I have a DS3 circuit from my router to the isp . I see Tx Discards time to time , I would like to implement some traffic shaping to capture the burst of traffic that exceed DS3 bandwidth and do show policy-map interface , I just don't know how to do it. I hope you do.

Thanks Again.

[Charles Hill]

In addition to the what has been stated,

you can show controller g0/1 utilization(if your ios permits this command)

This will show the bandwidth percentage that is being utilized.

Below is a link that provides tx discards troubleshooting steps.

http://hasanmansur.com/2012/12/15/layer-2-discards-troubleshooting-rx-tx-discards/

[cisco steps]

Very informative Hassan,

I am still looking for a policy command that can help configure traffic shaping and from that policy I should be able to tell how much traffic was above my 44 mg

[Charles Hill]

Hello Cisco Steps,

The link below describes how to configure traffic shaping on an interface that connects to the ISP, which is providing 30M. 

http://networkengineering.stackexchange.com/questions/6823/isp-edge-router-configuration

 One problem I have ran into several times is a speed duplex mismatch on the link between the CPE and the ISP. 

Both sides need to be hard coded or both sides to be set to auto.

Hope this helps.

[cisco steps]

I think I found this "Configuring Class-Based Shaping" http://www.cisco.com/c/en/us/td/docs/ios/12_2/qos/configuration/guide/fqos_c/qcfcbshp.html#wp1004483

Just need to confirm from the Network pro in this forum if that is what I need , any one with knowledge about the subject.

Thank you,

[Joseph W. Doherty]

Disclaimer

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Posting

If you are over running your available buffers, and you've a full DS3 running on a serial interface (at 45 Mbps), shaping isn't going to help.  (The physical interface is already effectively shaping.)

(You want to use shaping when you know downstream bandwidth is less than your physical interface.  For example, if your local interface is a FE, but downstream you know your traffic will cross a DS3 [which you do not manage], then you might benefit by shaping your FE at the DS3 rate.)

What might help, if the drops are due to short lived transient bursts, is increasing the egress queue depth.  This might reduce transmission drops, although it was also increase latency.

If the drops are more due to longer term transmission rates, an improved drop policy, such as WRED, or per heavy flow drops (e.g. FRED, WFQ tails drops), might mitigate overall drops.  (NB: BTW, WRED appears simple to configure, but getting it "right", isn't always so simple.)

[cisco steps]

Hi Joseph

Here is what I have one of my router.

show run

policy-map SHAPING-policy
 class class-default
  shape average 44000000
  fair-queue

------------------------------------------------------------------------

RTR1#show policy-map int s1/0
 Serial1/0

  Service-policy output: SHAPING-policy

    Class-map: class-default (match-any)
      2027581751 packets, 1581659631646 bytes
      30 second offered rate 3776000 bps, drop rate 0 bps
      Match: any
      Traffic Shaping
           Target/Average   Byte   Sustain   Excess    Interval  Increment
             Rate           Limit  bits/int  bits/int  (ms)      (bytes)
         44000000/44000000  275000 1100000   1100000   25        137500

        Adapt  Queue     Packets   Bytes     Packets   Bytes     Shaping
        Active Depth                         Delayed   Delayed   Active
        -      0         2027232974 591932674 4163801   1750621386 no
      Queueing
        Flow Based Fair Queueing
        Maximum Number of Hashed Queues 256
        (total queued/total drops/no-buffer drops) 0/449/0

Can you please show me what was done on the config and what I should look for when executing show policy-map int s1/0

Thank you in advance

[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

You've 449 drops out of 2,027,581,751 packets?!  If true, you don't really have a drop problem.

In any case, if your serial 1/0 is a physical DS3, again, you don't need to shape.  I.e. you can use your policy, as is, just remove the shape statement.

Also again, as you have few drops, your default FQ is probably just fine, however if you want to try to further decrease drops, you might see if the queue-length command is supported.  (Not all platform IOS versions do.  Often the defaults are optimal for T1/E1 links, and so for higher bandwidth links, like a DS3, they can be increased.)

PS:

BTW, understand, your very low drop rate might actually indicate you're transaction flows are not taking full advantage of all your WAN bandwidth; not uncommon on higher bandwidth WAN links.

[cisco steps]

Thank you very much for you time Joseph, greatly appreciated,  as you can tell I am newbie with Wan links and still have a couple of questions

I would like further decrease drops.

1. what command should I use if my IOS version support queue-length?.
2. what will happen if I remove the shape statement ?
3. what you mean by transaction flows are not taking full advantage of all your WAN bandwidth, how can that be corrected ?

Thank you in advance 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

what command should I use if my IOS version support queue-length?.

I recall (?) it's queue-length, but under the policy class-map use a question mark and see what commands are available.

what will happen if I remove the shape statement ?

Queue(s) will form when the physical interface congests. (Which works "better" than software based shaping.)  Software based shaping is useful when you have a need to slow the traffic below what the physical interface supports.  For example if you had a HQ frame-relay with a T3 connection but remotes sites only have T1 connections, you could shape, at the HQ's side, for the remote's bandwidth.

what you mean by transaction flows are not taking full advantage of all your WAN bandwidth, how can that be corrected ?

Suggest you (Internet) research LFN's (long fat networks) and TCP RWIN configurations.  (You'll find much better information than I'll be able to present in a paragraph or two.)