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Could someone tell me what do ifinDiscards (.1.3.6.1.2.1.2.2.1.13) and ifOutDiscards (.1.3.6.1.2.1.2.2.1.14) exactly mean?

Thanks.

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    Depending on the device/interface type, these are the numbers of discarded ingress or egress frames/packets. Egress packets are discarded when the queue overflows and ingress packets can be discarded when there's no route to the destination, a checksum failure, VLAN mismatch, ... – Zac67 Jan 17 at 16:17
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    @Zac67 You should make this an answer. – Ron Trunk Jan 17 at 16:28
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As RFC2863 / IF-MIB describes:

The number of inbound/outbound packets which were chosen to be discarded even though no errors had been detected to prevent their being deliverable to a higher-layer protocol. One possible reason for discarding such a packet could be to free up buffer space.

An interface discard is simply where the device has decided to discard a packet for some reason. The reason a device discards the packet(s) / frame(s) is typically hard to tell. It could be a corrupt packet, that the device is busy, buffer overflows, packet size issues, and several other things.

In another word, your interfaces could be overloaded or receiving too much burst data for the buffers to pass to the physical interface. These count as discards.

However, if it happened on a switch, buffer drops are a normal part of switching and you don't need to be concern about that.

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(converted from comment)

Depending on the device/interface type, these are the numbers of discarded ingress or egress frames (for switching devices/ports)/packets (for routing devices/ports).

Egress packets are discarded when the queue overflows (on congestion) and ingress packets can be discarded when there's no route to the destination, a VLAN mismatch, a checksum failure, ...

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