alot of output drops after applying Qos

[ahmadali7]

Hi Guys,

I have issue when I  apply "mls qos"  in the switch , the output drops start come in solarwinds and in the interface it self.

I have configured the interface(ethernet 1Gb) as below:

interface gig 0/1

speed 10

srr-queue bandwith limit 50

to get 5 Mbps downlad .

is this will make a network congestion or its normal (Output drops)?

if there is a way to stop the output errors please advice me?

Thanks in advance

[paul driver]

Hello

Can you elaborate on the 5mb download limit - Have you tied increasing this limit?

Is this interface connected to a wan interface or just running as an access port on the switch

res

Paul

[ahmadali7]

Thanks dear Paul for the reply.

actually, I want to limit the download for each user to 5Mbps ,thats why I have changed the speed of interface to 10 MB  and limit it 50% to get 5Mbps for every one ,

but the problem is output drops(Transmit discard)

always increasing, I want to stop it.

yes this interface connected to access port in a switch (WS-C3560X-48P)

Appreciate your coopration 

Regards,

Ahmad Mestarihi 

[shaps]

the output drops could be related to the buffers being overloaded,  if you have shaped the port to be 5mb then the buffers will be filling up when users are trying to download anything of any great size, especially if there are a lot of users. 

[ahmadali7]

Hello Shaps1983,

  Thanks for the reply,yes I have over 200 users. could you suggest me commands to do this?

Do I have to change the speed of the interface or no?

Thanks in advance

Appreciate your coopration 

Regards,

Ahmad Mestarih

[shaps]

if you have 2 hundred users through the switch all on 5mb ports then the buffers would soon become full,  if these ports are just for  lan use then its probably better to allow the ports to work and full speed, what is the main reason for limiting the speed ?

[ahmadali7]

Hello shaps1983,

the Idea of limiting the speed of the internet for some users  is to keep the internet speed very good for the mangers  and very high speed.

our mangers always complain about internet speed very slow , so when I limit the internet speed for the normal users , the mangers will get the high speed right?

Appreciate your coopration and advice 

Regards,

Ahmad Mestarih

[Joseph W. Doherty]

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Posting

The 3560/3750 series are a bit infamous for  egress drops when there's congestion on the interface especially when QoS is enabled with their default QoS settings.

If your congestion is transient/bursty, QoS tuning can sometimes mitigate.  Also what might help is careful selection of which port is being used (as 2MB of buffer RAM is allocated per 24 edge ports or for the uplink ports).

[ahmadali7]

Hello Joseph,

 the output drops not bursty, it increases slowley over the time. Actually, I am aware of all ports that I have applied the command " srr-queue bandwidth 50"

note that I have changed the speed of the interface(1Gb)  to 10 MB and used the command

" srr-queue bandwidth 50" to make the download to 5 Mbps. like below:

interface gig 0/1

speed 10

srr-queue bandwith limit 50

 is there is any command you can suggest me to configure?

my target is  to get 5 Mbps as download for each users.

Thanks in advance

[Joseph W. Doherty]

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 wha2tsoever (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

My reference to bursty was the traffic is bursty, not so much the drops, although they too might appear in clusters with a traffic burst, if the traffic is bursty.

I'm a bit confused.  So, you shaped each user port?

Could you clarify your topology?

[ahmadali7]

Actually,there is no bursty with traffic . I didnt make shaped with interface . only change the speed (to 10)and put command "srr-limit bandwidth 50".

if you think the shaped will solve please advice me the commands and the right speed?

I have read that output drops not a real errors , and its not a big deal when you configure policy (srr-queue) is that correct ?. becouse solarwinds shows alot of transmit discard .

I have big network alot of services and vlans , 2 primary  cores, 2 more standby core.
I want to give command to limit capacity and speed of the internet for some users by ports of switches , like as I said 5 Mbps download .

I hope you get a good idea of what I need .

Appreciate your cooperation
Regards,
Ahmad Mestarihi

[Joseph W. Doherty · Accepted solution]

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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.

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In no event shall Author be liable for any damages wha2tsoever (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

On a 3750, running the interface at less than full port speed, using the limit command, is still effectively shaping.

Doing what you're doing on edge interfaces seems like a worthwhile idea, but it's not as much as it would appear, for a couple of reasons.  First, although, indeed, a user won't see more than 5 Mbps, that doesn't directly slow the upstream's down transmission rate.  What will happen, your ISP link can saturate your link even after/concurrently with your edge port being a bottleneck and queuing packets on the edge interface.  Enough of that, you'll drop packets, which on some protocols will "tell" the sender to slow its transmission rate, but there's lot of lag to that feedback.  Faster feedback to the sender would be to police the edge port's egress, but I don't believe that's possible on a 3750.

Second, since you're running the interface, effectively at 5 Mbps, you're slowing all/any local traffic to that speed.  A way to avoid that would be to run the interface at full bandwidth, mark ingress ISP traffic, direct that marked traffic to a "dedicated" queue shaped at 5 Mbps.  This will avoid impacting non-ISP traffic.

Lastly, how many users might "pull" concurrently.  Can their aggregate exceed your downstream bandwidth capacity?

BTW, don't misunderstand, I'm not saying what you're trying won't help at all, just it likely won't help as much as you would like.

PS:

Oh, if you use a dedicated shaped queue, for Internet traffic, by decreasing its buffers, it will behave more like a policer.

[ahmadali7]

Hello Joseph W. Doherty ,

I would like to thank you for the full explanation.

Actually , the problem we have in our organization that we have alot of users (over 200) and many users use the downloading and this will effect the download speed for the others ,especially the managers(always complain about slow internet) . As you said this will affect the local speed like shared folder in the servers , but not aproblem for us. so thats why I did this idea.

I will do with ur advice and use the full speed but make shaping to the queue , last thing could u provide me a documents or write a command that I can try , if possible ?
again many thanks goes to you

Appreciate your cooperation
Regards,
Ahmad Mestarihi

[Joseph W. Doherty]

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 wha2tsoever (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

Ahmad, most of the information you need is contained in the Cisco reference or usage guides for your 3750 IOS; also Cisco's tech notes and white papers on 3750 QoS.

What you won't find in Cisco documentation (as far a I know) is a direct example of using 3750 QoS as I described.  Unfortunately, I don't have the time to work up an example for the specific "how to do it", using actual 3750 configuration statements; sorry.

[ahmadali7]

Hi Joseph,

   speical thanks to you , I was just looking for a doucuments that can help me or your advice  . really , I dont want to take more time and efforts from you and I appreciate your cooperation.Thanks 

Regards,

Ahmad Mestarihi