Posted on October 11, 2018 6:12 pm
 |  Asked by Tommy Kim
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I would like to know how to set my DCS-7060CX2-32S-F (4.20.7M-8944203.4207M) to drop packets with errors.

TK100G2(config)#sh int eth 1/1-6/1 counters errors
Port FCS Align Symbol Rx Runts Giants Tx
Et1/1 7 0 10 7 0 0 0
Et2/1 25 0 26 25 0 0 0
Et3/1 0 0 0 0 0 0 138
Et4/1 0 0 0 0 0 0 44
Et5/1 141 0 141 141 0 0 9
Et6/1 46 0 46 46 0 0 15


Posted by Alexis Dacquay
Answered on October 16, 2018 9:39 am

Hi Tommy,

In standard networking, packets are stored then checked before being forwarded. That switching method is called “store-and-forward”.
In cut-through mode, as many switches operate nowadays, the packets are forwarded before being completely checked, which requires storing it. The beginning of the frame is effectively forwarded before the switch knows whether the frame in its entirety is valid or not.

But why do you care?
From a switch perspective it would be much more taxing (latency-wise in store-and-forward mode) to resolve this than just passing it.

The problem is not on the switch, it is elsewhere: either on the sending host, or on the faulty links. These are the places to resolve the root cause.

If the ‘bad’ frames count is very low then you may ignore it from a switch perspective, albeit you should resolve it at the root cause.
If the rate is high and you think it is important for the switch to stop propagating these, then you must use a store-and-forward switch.

Most switch-on-a-chip network devices nowadays are cut-through, so make sure you check what model would suit you. At Arista for example, the R-series and 7160S have a store-and-forward architecture.

Best regards,

Posted by nick
Answered on October 17, 2018 1:13 pm

You can configure the 7060X2 to drop Ethernet errors by changing it’s forwarding mode to store and forward via:

switch forwarding-mode store-and-forward

Note that this will cause the switch chip forwarding agent to restart so it will impact traffic.

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