Cisco 3750e Only has Output Drops When Connected to NetApp FAS6080

[matthewsl]

We have been been troubleshooting output drops on interfaces on a Cisco 3750E that connect to numerous Netapp FAS6080 filers. We use througput test devices to send data directly to a netapp and to a netapp through a Cisco 3750e switch. The switch interface generates output drops. However, the switch doesn't create output drops when the netapp is replaced with a server or a laptop. So the issue of output drops occurs when a specfiic NetApp device is sending/receiving data with a Cisco 3750E switch. Additionally, We don't have the issue with a Cisco 3750G switch. Does NetApp have something listed in the compatibility matrix or is this new?

Thanks!

Matt

[mitchells]

How does your flow control look?

[matthewsl]

We turned off flow control completely on the cisco interface and the netapp and

we still have the same issue. It almost seems like there is flow control though

it is turned off.  Anyway we can trick the netapp and cisco to workthrough the

flow control, if it is the issue?

[kevingraham]

matthewsl wrote:
The switch interface generates output drops. However, the switch doesn't create output drops when the netapp is replaced with a server or a laptop

At the same throughput levels? Which interfaces are recording drops?

[mitchells]

You want flow control set to full rather than none.

What's the output from ifstat -a?  That will list the negotiated flow control status on your interfaces.

Thanks,

Mitchell

[matthewsl]

The original design was over portchannels configured for ip not mac addresses

load balancing. However, we removed the port channels and just ran over a single

interface and got the same problematic output drops.

[mitchells]

I would still be interested in seeing your flow control setup.

[matthewsl]

The netapp admins say "i've turned off flow control". Quick question. I want to

put an ACL on the interface basically limiting ftp tcp 21/22 and bare minimum,

say block the flow control ports. What socket is used for the netapp flow

control?

[mitchells]

A socket happens at layer 5 of the OSI model.  Ethernet Flow Control happens at layer 2.

Flow control enables you to manage the flow of frames between two directly connected link-partners. Flow control can reduce or eliminate dropped packets due to overrun.

To achieve flow control, you can specify a flow control option that causes packets called Pause frames to be used as needed. For example, link-partner A sends a Pause On frame to link-partner B when its receive buffers are nearly full. Link-partner B suspends transmission until it receives a Pause Off frame from link-partner A or a specified timeout threshold is reached.

http://now.netapp.com/NOW/knowledge/docs/ontap/rel733/html/ontap/nag/GUID-ED84D07C-609C-44E5-AC75-6E7FF282B557.html

This sounds like what you are experiencing.  Turn on Ethernet flow control and your issue should go away.

Thanks,

Mitchell