PfR has three monitoring modes of operations, namely
● Active mode: uses IP SLA probes
● Passive mode: uses NetFlow
● Fast mode: uses IP SLA probes (based on FRR feature)
No explicit NetFlow or IP SLAs configuration is required; support for NetFlow and IP SLAs is enabled and configured automatically by the master controller. You can use both active and passive monitoring methods for each traffic class. The master controller uses both passive and active monitoring by default. All traffic classes are passively monitored using integrated NetFlow functions, whereas the OOP traffic classes are actively monitored using IP SLA functions.
Passive monitoring metrics include the following:
● Delay: Cisco PfR measures the average delay of TCP flows for a given prefix or traffic class. Delay is the measurement of the round-trip response time (RTT) between the transmission of a TCP synchronization message and receipt of the TCP acknowledgement.
● Packet loss: Cisco PfR measures packet loss by tracking TCP sequence numbers for each TCP flow; it tracks the highest TCP sequence number. If it receives a subsequent packet with a lower sequence number, PfR increments the packet-loss counter. Packet loss is measured in packets per million.
● Reachability: Cisco PfR measures reachability by tracking TCP synchronization messages that have been sent repeatedly without receiving a TCP acknowledgement.
● Throughput: Cisco PfR measures throughput by measuring the total number of bytes and packets for each interesting traffic class or prefix for a given interval of time.
Active monitoring metrics include the following:
● Delay: Cisco PfR measures the average delay of TCP, User Datagram Protocol (UDP), and Internet Control Message Protocol (ICMP) flows for a given traffic class or prefix.
● Reachability: Cisco PfR measures reachability by tracking TCP synchronization messages that have been sent repeatedly without a received TCP acknowledgement.
● Jitter: Cisco PfR measures jitter, or interpacket delay variance, by sending multiple packets to a target address and a specified target port number and measuring the delay interval between packets arriving at the destination.
● MOS: MOS is a standards-based method of measuring voice quality.
Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 6238-6243). . Kindle Edition.