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High Discard Rate Value on DWDM connections ?

jjpeyrache
Level 1
Level 1

hello all gurus,

i have an customer issue on 3750-E-48 connected to DWDM link

my NMS reports sometimes very huge of Discard Rate Value on DWDM's port of 3750

DWDM link is configured at 1G speed and % of usage is approximalty alway 10 to 20

so i think link is not oversucribed

i looked on 3750 counters but nothing wrong from that

where can i dig to find culprit on that  issue ?

thanks in advance

JYP

7 Replies 7

Joseph W. Doherty
Hall of Fame
Hall of Fame

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

The 3750 series is a bit infamous for egress dropping transient burst packets.

Do you have QoS enabled?  If so, and if you don't need it, disable it.

If you need QoS, buffer tuning may mitigate your egress drops.

thanks this answer

we don't use QOS yet,

do you have any documents or pointers regarding 3750 series egress buffers/queues usage/issue ?

that may help to understand correctly customer issue

i need propose some quick workaround to my customer without replacing 3750 switches of course

thanks

JYP

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

https://supportforums.cisco.com/document/31581/egress-qos

thanks

i'll check that carrefully

JYP

i read attached documentation and still searching and solution

since DWDM link is not full i can't apply QOS for that point

any help/examples  welcomed to tune fine ingress buffer on 3750E

thanks

JYP

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

I understand your confusion, i.e. thinking low utilization won't lead to drops; not always so.  Suggest you search Internet on subject of micro bursts.

ok thanks

i'll do that

JYP

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