Adaptive Sampling - Juniper EX9200 Features Manual

Network Management and Monitoring Feature Guide for EX9200 Switches

Adaptive Sampling

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NOTE: sFlow technology on the switches samples only raw packet headers.
A raw Ethernet packet is the complete Layer 2 network frame.
An sFlow monitoring system consists of an sFlow agent embedded in the switch and a
centralized collector. The sFlow agent's two main activities are random sampling and
statistics gathering. The sFlow agent combines interface counters and flow samples and
sends them across the network to the sFlow collector in UDP datagrams, directing those
datagrams to the IP address and UDP destination port of the collector. Each datagram
contains the following information:
The IP address of the sFlow agent
The number of samples
The interface through which the packets entered the agent
The interface through which the packets exited the agent
The source and destination interface for the packets
The source and destination VLAN for the packets
EX Series switches adopt the distributed sFlow architecture. The sFlow agent has two
separate sampling entities that are associated with each Packet Forwarding Engine.
These sampling entities are known as subagents. Each subagent has a unique ID that is
used by the collector to identify the data source. A subagent has its own independent
state and forwards its own sample packets to the sFlow agent. The sFlow agent is
responsible for packaging the samples into datagrams and sending them to the sFlow
collector. Because sampling is distributed across subagents, the protocol overhead
associated with sFlow technology is significantly reduced at the collector.
NOTE: You cannot configure sFlow monitoring on a link aggregation group
(LAG), but you can configure it individually on a LAG member interface.
NOTE: If the mastership assignment changes in a Virtual Chassis setup,
sFlow technology continues to function.
The switches use adaptive sampling to ensure both sampling accuracy and efficiency.
Adaptive sampling is a process of monitoring the overall incoming traffic rate on the
network device and providing intelligent feedback to interfaces to dynamically adapt the
sampling rates on interfaces on the basis of traffic conditions. Interfaces on which
incoming traffic exceeds the system threshold are checked so that all violations can be
regulated without affecting the traffic on other interfaces. Every 12 seconds, the agent
checks interfaces to get the number of samples, and interfaces are grouped on the basis
of the slot that they belong to. The top five interfaces that produce the highest number
of samples are selected. Using the binary backoff algorithm, the sampling load on these
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