Troubleshooting Tip: How to interpret RX drops on FortiSwitch devices

[Adolfo_Z_H]

Description	This article describes RX Discard counters on port statics and which kinds of packets FortiSwitch OS includes on it.
Scope	All FortiSwitch models and versions.
Solution	Some customers observe RX Discard packet count increases over time. This depends on port configurations. Port51 and port52 are both members of ICL MCLAG trunk, meaning the Rx Discard count will have large numbers.     edit "_FlInK1_ICL0_"         set mode lacp-active         set auto-isl 1         set mclag-icl enable         set members "port51" "port52"     next     port51 Port Stats:         Rx Bytes: 3859959205219         Rx Packets: 4102187506         Rx Unicasts: 4091427311         Rx NUnicasts: 10760195         Rx Multicasts: 5318619         Rx Broadcasts: 5441581         Rx Discards: 4099935 <==== Packet drop     port52 Port Stats:         Rx Bytes: 1900858591287         Rx Packets: 2419162739         Rx Unicasts: 2405248197         Rx NUnicasts: 13914542         Rx Multicasts: 6741143         Rx Broadcasts: 7173398         Rx Discards: 47149 <- Packet drop. Due to FortiSwitch software design, FortiSwitch will include lots of legitimate packet discards, such as ICL egress blocking, STP blocking, FortiLink protocol packet blocking, ACL blocking, etc. in Rx/Tx Discard count. As a result, it will trigger a false alarm in a network monitoring tool or cause concern for network administrators. It is normal to observe less than 1% of the total packet process count as a value on RX packet drops. It is because these packets are processed by CPU instead of being transmitted back to the network. The amount of packet discards will be very dependent on the port configuration, but it is expected that uplink ports and other ports connected to third-party devices using those protocols will display this behavior. It is recommended to adjust the threshold baseline on monitoring tools accordingly or just monitor CRC errors instead. However, if concerns persist and packet discard increases above the limits mentioned here or there are network issues, open a TAC ticket to confirm and get support on this matter.