[c-nsp] 3850 and output drops

[Adam Baxter]

This is probably the bug that I found recently.....

https://bst.cloudapps.cisco.com/bugsearch/bug/CSCva81608





On 7 September 2016 at 06:07, Peter Rathlev <peter at rathlev.dk> wrote:

> On Tue, 2016-09-06 at 18:48 +0200, Sebastian Beutel wrote:
> > Everything started when a co-worker tried to troubleshoot a rapidly
> > increasing output error counter on a 3850 Switchport.
>
> What kind of interfaces are these? Would it perhaps be downlink
> interfaces that connect at a lower rate than the uplink interface on
> which traffic arrives? This will exercise the output buffers.
>
> What does "show interface <...> counters errors" say? If the errors are
> "OutDiscard" then it's a buffer problem. Otherwise the kind of drops
> should indicate where to continue troubleshooting.
>
> Are there any service policies configured on the interfaces? If so,
> then "show policy-map interface <...>" might shed some light on why the
> drops occur.
>
> You can see hardware counters for an interface with
>
>   show platform qos queue stats Gi 1/0/29
>
> The space between "Gi" and "1/0/29" seems to be necessary at least in
> IOS XE 3.3.5.
>
> You might want to take a look at
>
>   "Catalyst 3850: Troubleshooting Output drops"
>   http://www.cisco.com/c/en/us/support/docs/switches/
> catalyst-3850-series-switches/200594-Catalyst-3850-
> Troubleshooting-Output-dr.html
>   (http://tinyurl.com/z6acheu)
>
> There's an example (last "Example 2") policy-map for just assigning
> maximum buffers to a single default queue. There are certain caveats
> but IMHO something like that should be default on user facing network
> interfaces.
>
> --
> Peter
>
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