3750-x - Output Drop

[Tauer Drumond]

Hey all,

I dont know what else to do.

We have a 100Mbps metro-ethernet link connecting to a remote site. This link is terminating in our 3750-x stack switch.

We are getting a LOT of output drop on that interface and our remote IP Phone calls keep going off because of that.

I've disabled all kind of QoS, but no luck

Can someone give an idea?

Thank you all

[Joseph W. Doherty]

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Posting

I've disabled all kind of QoS, but no luck

"Disabled"?  If true, that could be the problem as normally guaranteeing VoIP performance requires QoS.

If, instead, you meant you've tried all different kinds of QoS, would need more information about what you've tried and what's the topology.

[Leo Laohoo]

CSCtq86186

[david.tran · Accepted solution]

Or you may run into a "microburst" problem. 

It is an issue that is very hard to detect unless you hook an sniffer and span that port and capture data on that port, then export the data and  use wireshark to look for microburst.

Cisco TAC wrote a very detail powerpoint presentation on this, about 8 pages, with nice graph and explaination.

I ran into an issue similar to this one about three months ago and it turns out that this is a limitation with 3750 hardware.  Recommendation from Cisco, X4500 devices which turn out to be a correct choice.

[Tauer Drumond]

Hi David,

do you have this Cisco PowerPoint presentation about this issue?

[david.tran]

if you provide me with an email address, I can send it to you.

[Tauer Drumond]

Hi david,

here is my e-mail: tauerfelipe@gmail.com

Thank you

[tguilbault]

Hi david

Will it be possible to email me the TAC presentation at my email guilbault.thierry@club.fr

Thanks in Adavance

Thierry

[tedwang1968]

David,

        Can you mail me the PowerPoint presentation too , thank you.  my mail: eng.ted@gmail.com

[ssvensson]

Hi David.

Would it be possible for you to provide me a copy of the presentation you have mentioned bevore ?

svensson@netcloud.ch :-)

Regards,

Sylvio

[nspasov]

To add to all of the other good inputs: I assume that your end user ports are all 1Gb. If so then microburts are definitely possible as your traffic is going from 1Gb ports down to a 100Mb. If that is the case QoS with some traffic prioritization and traffic shaping/policing could very well solve your issue.

[shillings]

I think the latest 15.0(2)SE IOS will help on a per-port basis too, although not sure it will be enough of an improvement - I imagine it will depend on the size of the burst.

It's still very early days for that version though, so there are risks involved.

[Tauer Drumond]

I've been monitoring that port... using Wireshark, and I had so many bursts..

This link terminate in a 6509 switch too... and we dont have drop at this switch... only in my side: 3750-x

routed                           routed
port         100Mbpslink    port

6509 --------------------------- 3750-x (output drop only here)

[nspasov]

If microburts are the cause of your drops then that is to be expected. The buffer size on the 6500 switch is much larger than the ones on the 3750/3750-X. Thus, the 6500 can handle the extra burst while the 3750 buffers get filled any additional packets will get tail dropped. Can you post the output from "show buffers" and "show proc cpu his" on your 3750?

[Tauer Drumond]

Hi... please see attachment