CISCO CCNA Exam – Q268

What are three values that must be the same within a sequence of packets for Netflow to consider them a network flow? (Choose three.)

A. source IP address
B. source MAC address
C. egress interface
D. ingress interface
E. destination IP address
F. IP next-hop

Correct Answers: A, D, E

Each packet that is forwarded within a router or switch is examined for a set of IP packet attributes. These attributes are the IP packet identity or fingerprint of the packet and determine if the packet is unique or similar to other packets.
Traditionally, an IP Flow is based on a set of 5 and up to 7 IP packet attributes.

IP Packet attributes used by NetFlow:
• IP source address
• IP destination address
• Source port
• Destination port
• Layer 3 protocol type
• Class of Service
• Router or switch interface

All packets with the same source/destination IP address, source/destination ports, protocol interface and class of service are grouped into a flow and then packets and bytes are tallied. This methodology of fingerprinting or determining a flow is scalable because a large amount of network information is condensed into a database of NetFlow information called the NetFlow cache.