04-16-2015 10:53 AM - edited 03-07-2019 11:35 PM
Hi
I am facing packet loss on a port and wondering if anyone has any suggestions. I have a 2960x stack of 2 connected to a 6880 vss pair using a port-channel with 2 x 1g links
6880 ----------------------------- 2960x
-----------------------------
2 x 1G Port-channel
On the 2960x, packets are dropping on both ports, but a lot more on one of the ports.
Its not a bandwidth issue as bandwidth is not fully utilized on the link, more case of quantity of packet filling the hardware queue and dropping I believe. We have introduced a third link into the port channel, and also executed the src-dest command for load balancing traffic evenly over each link in the port-channel but still dropping packets but not as heavily as before.
Has anyone experienced something similar and may be able to recommend anything. BTW the 2 links terminate one on each 2960x and on each 6880 vss pair.
Thanks
04-16-2015 12:00 PM
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
Its not a bandwidth issue as bandwidth is not fully utilized on the link, more case of quantity of packet filling the hardware queue and dropping I believe.
What causes packets to fill a queue? A. Insufficient bandwidth; that's why they are being queued.
That said, there's a lack of transient bandwidth and a lack of long term bandwidth. The latter generally needs to be addressed by adding bandwidth, but the former might be addressed by providing sufficient queuing.
Do you have QoS enabled? If so, and you're not really using QoS, disable it.
If you're are using the QoS, buffering can be "tuned". What I've found seems to help on the 3750s (much similar to 2960s), is moving buffer resources from interface reserved to the shared pool. This allows low usage ports to provide their unused buffers to high usage ports.
04-17-2015 01:43 AM
Thanks Guys,
Yes it is a LACP port-channel, Il try getting the output for sh etherchannel load, im not at the site right now.
@Joseph, yes you're definitely right about the bandwidth, but I have added another 1g link to the port-channel which now only shows packets dropping on one of the 3 ports in the port-channel. QOS seems to be enabled here and there and not being used by the looks of it, which may be part of the issue.
Il try getting a packet capture to see if that shed any light on it.
Thanks
04-17-2015 08:37 AM
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
If QoS isn't being used, the reason I suggested disabling it, is because QoS reserves buffers for four, per port, egress queues.
04-16-2015 12:02 PM
Hi,
Are you running LACP on the Portchannel?
By default, the 2960-X series switch use src-mac, and this works just fine for most situations?
What is the output of "sh etherc load"?
HTH
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide