What causes interface discards?

[Chris7]

I am seeing a high number (100k+/30 sec) of in(put) discards on one of the 10.0G switch interfaces on my S4 going to an N7. I went looking for input errors on the port, but there are none, and the interface is running at about 5% utilization. So, what is a discard, and how do I troubleshoot it? Note: The out(put) discards appear to be zero.

[Chris7]

GTAC is currently investigating the possibility that there are pause frames on the link.

[Zdeněk_Pala]

What about option that you are receiving tagged frames for non-existing VLAN?

Z.

[Doug]

Chris,

Can you contact the GTAC so we can open a ticket for tracking? If you want, send me your contact info directly and I will have a ticket opened and assigned for a callback.

dhyde@extremenetworks.com

-Doug

[Chris7]

Doug, I checked the port egress on both sides of the link in question with "show port egress". There was one VLAN on either side that was mismatched, but on both sides the VLAN was just on that one port. Regardless, I've tweaked those two VLANs so the lists on both sides of the fibre link match exactly, and the issue is still occurring.

[Doug]

Typically a frame is discarded inbound if the switch determines it does not need to forward that frame. One common issue to look for on an uplink is if you are egressing a vlan from the partner switch that is not configured on the switch that reports the discard traffic inbound. The receiving switch does not need to forward that vlan traffic so it discards the frames.