Switchport Counters - Take two

Jim Glassford jmglass at iup.edu
Thu Mar 27 17:06:03 UTC 2014


I have no experience with a Nexus 4001i, seems this could be counting up 
due to frames of no interest, wrong VLAN, Spanning tree, other.
Not by chance on a IBM BladeCenter?

<http://www-947.ibm.com/support/entry/portal/docdisplay?lndocid=MIGR-5093165&brandind=5000020>

The "input discard" counter on any internal interface (Ethernet1/1 - 
Ethernet1/14) may increment on Cisco Nexus 4001i switches, even when the 
connected blade is started into Unified Extensible Firmware Interface 
(UEFI) and not sending Operating System (OS) data.
This has been observed with QLogic Dual-Port 10 GB Converged Network 
Adapter (CFFh) for IBM BladeCenter, Option part number 42C1830, but may 
occur with other Network Interface Controllers (NICs).

Workaround:
This is a reporting issue. The 'input discards' are not counting actual 
packet loss.
Do not replace any hardware or update firmware.


On 3/27/2014 12:51 PM, rwebb at ropeguru.com wrote:
> Apologies to everyone for the original email with no subject. I am 
> having some senior email moments today.
>
> Anyway....
>
> 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.
>
> 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
>




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