Cisco standard NetFlow version 5 defines a flow as a unidirectional sequence of packets that all share seven values which define a unique key for the flow:
+ Ingress interface (SNMP ifIndex)
+ Source IP address
+ Destination IP address
+ IP protocol
+ Source port for UDP or TCP, 0 for other protocols
+ Destination port for UDP or TCP, type and code for ICMP, or 0 for other protocols
+ IP Type of Service
Note: A flow is a unidirectional series of packets between a given source and destination.