UCS B - VIF Paths : IOM NIF and HIF Troubleshooting

Introduction

We often talk about packet loss at HIF interface or NIF interface in IOM but how really this interface is tied with counter physical interface in FI and Blade? So the goal of this document is to help you to visualise the internal path from a blade to fabric interconnect via IOM or vice versa. Also, how to read these interface stats.

This document builds on from a previous document "UCS B - VIF Paths Understanding and troubleshooting".



Troubleshooting Steps

In this example we will look at the virtual circuit 1779. This virtual circuit connects vnic0 in a blade with interface vethernet 1779 in Fabric Interconnect.

What you see in UCSM above, we can visualise each interface element as below diagram. vnic0 automatically creates vethernet interface 1779 in Fabric Interconnect. It will maintains virtual circuit 1779 in orange dotted line. However, if there is any packet loss observed, we may need to look at some of stats  inside of the IOM.

Below is how to trace it. Basically we can start from "Server Port" in FI. This server port connect to NIF interface of IOM and HIF interface of IOM connects to vNIC0.

Next we need to identify the vNIC0 port. vNIC is shown as "FEX Host Port" in UCSM and in NXOS it shows as "Ethernet #/#/#" format in "show fex detail". So the FEX port is basically a blade interface representing vNIC. In this example as below, FEX Host Port 1/1/1. 

If we redraw this, it should be like below diagram :
- Yellow interface in FI-A represents the "Server Port" which is E1/17.
- Yellow interface in a Blade represents the "Fex Host Port" which is E1/1/1.

With the server port E1/17 and the Fex host Port E1/1/1 we can identify HIF and NIF port in IOM. We need to connect NXOS and run a following command.

- run "show show system internal fex info satport ethernet 1/1/1"
- As below cmd output,we see that Eth1/1/1 connects to HIF7. This HIF7 is pinned to NIF3. The NIF3 connects to the server port E1/17.

Now we can look at the IOM architecture and IOM cmd output to understand more clearly what is really happening for traffic flow.

From the Fabric Interconnect CLI, we need to connect IOM.

connect iom <chassis #>
show platform software redwood sts 

it shows a representation of exactly how the FEX is being used.
+ use "redwood" for IOM 2104. Use "woodside" for IOM 2104.
+ This command shows all the internal blade facing port known as "HIF - Host Interfaces" and all the network interface facing FI known as "NIF".
+ we see ASIC number as 0. This 0 will be used with rmon cmd later.

Check NIF interface stats to see if there is any outstanding error or drop facing to FI :

show platform software redwood rmon 0 nif3

Check HIF interface stats to see if there is any outstanding error or drop facing to blade :

In this example no packet error or drop is observed. However, if there is any loss or slow performance arised in UCS B Infrastructure, it is important to check and monitor NIF and HIF interface stats for IOM.