Lee ler762 at gmail.com
Thu Mar 27 16:55:46 UTC 2014

On 3/27/14, rwebb at ropeguru.com <rwebb at ropeguru.com> wrote:
> So I certainly admit I am a basic networking guy and in the past have not
> had to get into the nitty gritty of port statistics.
> I am trying to understand some statistics off a switch port in a Nexus
> 4001i.

Good luck.  I couldn't find anything for a nexus 4000, but did find
this for IOS:
In-Discard - The result of inbound valid frames that were discarded
because the frame did not need to be switched. This can be normal if a
hub is connected to a port and two devices on that hub exchange data.
The switch port still sees the data but does not have to switch it
(since the CAM table shows the MAC address of both devices associated
with the same port), and so it is discarded. This counter can also
increment on a port configured as a trunk if that trunk blocks for
some VLANs, or on a port that is the only member of a VLAN.

so if you've got something like
switch a: switchport trunk allowed vlan 1-5
switch b: switchport trunk allowed vlan 1-4

when switch a sends a frame on vlan 5, switch b counts it as an input discard.


> All TX and RX counters look normal except on the TX side, I am
> showing 1107597 input discards. Last clearing of show counters is 1d8h ago.
> I have it in my mind that this particular counter is dropping packets coming
> in from another port inside the switch that are to be transmitted out to the
> end server.
> So lets say the interface I am looking at is port 2 on the switch. So server
> 1 sends a packet to port 1 on the switch. That packet then traverses to
> backplane, or inside the same ASIC, to port 2 on the switch. It is then
> dropped and not transmitted out to server 2.
> Is the scenario I just presented correct? Not looking for the reason in this
> email, just that my logical understanding is correct.
> Robert
> Sent from my Verizon Wireless 4G LTE smartphone

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