Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 2087)

sFlow Introduction and Configuration
Software Reference for x310 Series Switches
C613-50046-01 REV A AlliedWare Plus TM Operating System - Version 5.4.4C 80.7
Configuration Procedure
The following process sets out a systematic procedure to configure sFlow on your switch:
Information Gathering
sFlow configuration is dependent on your network structure and its data. Start by
gathering together the following information.
■ Obtain (or determine) the sFlow collector IP address.
■ Select an appropriate UDP port for your sFlow datagrams. The recommended value is
6343, and is the default value preconfigured on your switch.
■ Select an appropriate IP address for your sFlow agent. We recommend that you use
the local IP address of your switch. For more information on local addresses and how
to set them up, see the
interface (to configure) command on page 12.3 .
■ Assess the sensitivity of the data that your sFlow agent will be sampling.
■ Obtain details of the protocols that your sFlow agent will be sampling. If you intend
sampling unusual or proprietary protocols, obtain details of their header lengths.
■ Calculate the most appropriate max-header-size for your sFlow sampling.
■ Select the ports that you want to sample, and their sample rate.
These two factors vary (not quite) proportionally; so if you double the number of
ports and double your sampling rate (i.e. sample half as many frames) then you will
“almost” return to your earlier situation. Also note the speeds of the ports you have
selected, because - for the same port utilization - the faster the port speed, the greater
the load on the CPU.
■ Review the speed of the port used to transport the sFlow datagrams to the collector.
Unless configured to a specific port, the collector traffic will share the same network
port with other traffic.
The capacity of the collector port should be sufficient to carry the volume of sFlow
traffic. This topic is expanded on in the
Configuration Examples later in this chapter.
Managing the sFlow processing overhead
The sFlow data sampled on the ports converges into the CPU for processing and UDP
packetizing. Therefore one of the major factors when configuring sFlow is to prevent the
sFlow data volumes from placing a significant overhead on the CPU processing. The two
most significant factors here are, the number of ports sampled, and the sampling rate.
The other (and lessor) factors in this equation are the frame size distribution and the
maximum header size. The shorter the frames are on the network, the heavier the sFlow
processing load will be (for the same number of frames per second). Conversely the
shorter the maximum header size selected, the lighter the sFlow processing load will be
(because less data per frame is sent to the CPU).