What load-balance method do you use? If you see an uneven distribution of output drops across the 2 L2 interface, consider changing the etherchannel load-balance method to have a more even traffic distribution (src-dst-ip for example).
I understand that you have 5 switches in the stack. You might consider spreading the etherchannel member interfaces across the stack members, in a way that the 2 ports should connect to different member switches (you can have the members on different members as cross-stack etherchannel is supported). This will ensure that you don't oversubscribe buffers on one port-asic (buffers are allocated per port-asic on 3750 switches). You might try to create a SPAN monitor session with the etherchannel member interfaces being the source ports to see if you find a burst of packets in a short interval which could lead to output drops due to buffer starvation. This will help you identify what's the source of the bursts. You might also look for unexpected or flooded traffic and consider pruning unnecessary vlans (if it's a trunk) to prevent flooding of broadcast and unknown unicast traffic on the etherchannel. Ultimately, you can increase the bandwidth by adding more links to the port-channel or using 10G links instead of GigabitEthernet. Best regards, Andras On Fri, Jan 14, 2011 at 10:08 PM, Robert VanOrmer <[email protected]> wrote: > I am experiencing a very similar issue on the C3750E platform w/ 12.2(52)SE. > We have 5 switches in a cluster, port-channeled with (2) Gig interfaces L2 > to distro (6500's) with excessive output drops even at low utilization. No > QoS enabled. I am using the Cisco TwinGig Converter Modules for uplinks.. > We have a TAC case open, but no progress yet. I'd be interested in knowing > if you find a cause. I am going to try swapping GBICs over the weekend. > > > > Thanks, > > Rob > > > >>Date: Fri, 14 Jan 2011 12:28:03 -0600 > >>From: Dan Letkeman <[email protected]> > >>To: Phil Mayers <[email protected]> > >>Cc: [email protected] > >>Subject: Re: [c-nsp] Constant output drops on etherchannel > >>Message-ID: > >> <[email protected]> > >>Content-Type: text/plain; charset=ISO-8859-1 > >> > >>3560 or 3560G. > >> > >>(C3560-IPSERVICESK9-M), Version 12.2(53)SE2 > >> > >>Interface config: > >> > >>interface Port-channel2 > >>switchport trunk encapsulation dot1q > >> switchport trunk native vlan 3009 > >> switchport trunk allowed vlan 8,10,1008,1101,3009 switchport mode trunk > end > >> > >>I see more output drops during higher traffic, but I still see drops during > low traffic rates. Always more on one interface. > >> > >>I do have auto qos enabled for some of the phones I have connected to the > switches, but I don't have any qos on the etherchannel trunks. > >> > >>I'm just using the default etherchannel load balancing algorithm. > >> > >>Thanks, > >>Dan. > > > > > > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ > _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
