How is sFlow packets routed?

[Jake]

Hi,

I'm not sure what is the best way to deploy sFlow.
1) Should the sFlow packets be routed on the same links as the data or should I have different links which are used only for the sFlow data (i.e. each switch has different ports for data and for sFlow traffic)?

2) Who is responsible to determine how is the sFlow packets routed from the switch to the collector? If it's an SDN network, I guess the controller should install rules for the forwarding of sFlow packets?

Thanks,

Jake

[Peter Phaal]

By design, the volume of sFlow traffic will be a small fraction of the
total traffic on the network (controlled by the sampling rate). The
sFlow datagram sending process is desynchronized across data sources
and agents and appears as random background traffic. Typically sFlow
will be to a collector on the management network (also used to carry
other control and management traffic - SNMP, ssh, netconf, OpenFlow
etc). In-band, the management traffic is typically tagged with its own
VLAN, or if the switches have capability, the traffic may be carried
on dedicated out of band network.

SDN networks require a way to connect the switch control plane to the
controllers. If you have that connectivity you should also be able to
receive sFlow over the same routed path.

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[Jake]

Thanks!

Regarding SDN, you assume that the sFlow traffic is routed to the controllers hence it can be router in the same way path that the switches and the controllers communicate.
But what is the sFlow collectors are separated from the controllers? for example, if you have several machines in the network which act as sFlow collectors.

[Peter Phaal]

You would typically want more than one controller for redundancy /
scaleability. The same network setup should allow for multiple sFlow
collectors on the management network.

It is also possible to use OpenFlow to replicate a sFlow streams to
multiple collectors:
http://blog.sflow.com/2013/11/udp-packet-replication-using-open.html