console: fix calculation of the L2 overhead when selecting L2 bps

console/clickhouse.go

@@ -190,7 +190,12 @@ func (c *Component) contextFunc(inputStr string) context {
 	case "l3bps":
 		units = `SUM(Bytes*SamplingRate*8)`
 	case "l2bps":
-		units = `SUM((Bytes+18*Packets)*SamplingRate*8)`
+		// For each packet, we add the Ethernet header (14 bytes), the CRC (4
+		// bytes), the preamble and start frame delimiter (8 bytes) and the IPG
+		// (~ 12 bytes). We don't include the VLAN header (4 bytes) as it is
+		// often not used with external entities. Both sFlow and IPFIX may have
+		// a better view of that, but we don't collect it yet.
+		units = `SUM((Bytes+38*Packets)*SamplingRate*8)`
 	}
 
 	c.metrics.clickhouseQueries.WithLabelValues(table).Inc()