Force10 S4820T Hardware drops explanation assistance

Question

Hello Community, When I issue a command to show hardware drops, I see constantly increasing counters in IngressDrops column, see the example below:

F10-ISCSI-R1#sh hardware stack-unit 0 drops unit 0 | grep ^.2[0-3]|UserPort
UserPort       PortNumber        IngressDrops    IngMacDrops     Ing-MMU-Drops   HOL-MMU-Drops   Aged-MMU-Drops  EgMacDrops      EgressDrops
 20              21              906211          0               0               0               0               0               14
 21              22              887033          0               0               0               0               0               74
 22              23              177527          0               0               0               0               0               25
 23              24              177602          0               0               0               0               0               37

We tried to set up a monitor session, however, it doesn't capture all packets, instead of this I see MMU Drops counter increasing:

F10-ISCSI-R1#sh hardware stack-unit 0 drops unit 0 | grep ^.19|UserPort
UserPort       PortNumber        IngressDrops    IngMacDrops     Ing-MMU-Drops   HOL-MMU-Drops   Aged-MMU-Drops  EgMacDrops      EgressDrops
 19              20              0               0               0               267537187       0               0               0

I'd appreciate it if anybody can assist with the hardware drops explanation on Force10 S4820T and S4810 switches.

What could be the reason for IngressDrops, if the link is barely utilized?

What does MMU Drops mean for running "monitor session"?

Outputs are from S4820T with SW 9.14(1.8)

DELL-Erman O · Answer

Hello,

What kind of devices are connected to the ports with the drops? I'm not 100% sure but it might be related to MAC addresses. Can you make sure that the MAC addresses are valid by checking your configuration,

Hope this helps!

murmanov · Answer

Hello Erman,

Thanks for your answer. We have different devices connected to ports that are showing IngressDrops, those are Dell Compellent, Force10 MXL switches, and similar types of devices. I didn't see any specific similarity or difference between connected devices, they look like regular devices connected to the network

Could you please elaborate on what did you mean by "valid MAC addresses"?

Best regards, Max

DELL-Joey C · Answer

Oh, and I forgot about the question on valid MAC addresses. Erman perhaps is referring to check if the devices connected to switch are detected by the switch with correct MAC addresses cross reference with the device MAC addresses.

murmanov · Answer

Hello Joey,

Speed connection and MTU settings are correct.

MAC addresses look correct, as well as LLDP neighborships with DELL storages

Unfortunately, I can't confirm if these drops were from the beginning. Regular interface counters were showing all zeroes.

We can't open a technical ticket since we don't have a support contract. Do you have any other documentation or articles you may suggest to me? Something like packet drops troubleshooting manual.

DELL-Joey C · Answer

Hi,

I spoke to one of my networking co-work briefly on your issue. Was this switch first deployed having issue or it was working before?

If you have an existing contract on the switch, I may suggest to contact support to verify the switch logs, storage device logs and other devices on where is the cause of the IngressDrops since you have mentioned that the ports have less traffic with package drops.

I also suggest to check the end to end ports if they are using the same speed connection and check the MTU values.

DELL-Joey C · Answer

Hi @murmanov,

Unfortunately, there is no troubleshooting documentation for such issues. It seems that you already have the latest OS installed, maybe if you would want, you can try installing a lower version of OS to check if it helps the issue.

I'm pretty sure you have also verified that the cables are good known, how about trying other ports of the switch? Does it make any difference? Do you have another S4820T to test the connectivity of the devices, if they are causing the issue?

murmanov · Answer

Hello Joey,

You're right. This switch is not the only one that has IngressDrops counters growing. We have six of 4820T switches in the production network used in the iSCSI network, and all report the same issue.

Four of them are on DNOS 9.14, and two of them are on DNOS 9.11.

So the only way to understand the root cause of these drops is to open a case with Dell Support?

murmanov · Answer

Hello Marco,  Thanks for the confirmation.

DELL-Marco B · Answer

Hello, I think what Joey is saying is that this is a complex issue that required to be followed by a tech support specialist that can analyze logs and make a remote session in case.  Thanks Marco

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Force10 S4820T Hardware drops explanation assistance

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