Monitoring System Statistics and Network Traffic with sFlow

sFlow is a monitoring protocol that samples network packets, application operations, and system counters. sFlow collects both interface counters and sampled 5-tuple packet information, enabling you to monitor your network traffic as well as your switch state and performance metrics. An outside server, known as an sFlow collector, is required to collect and analyze this data.

hsflowd is the service that samples and sends sFlow data to configured collectors. By default, hsflowd is disabled and does not start automatically when the switch boots up.

The hsflowd service does not sample interfaces that are up but not configured.

If you intend to run this service within a VRF, including the management VRF, follow these steps for configuring the service.

Configure sFlow

To configure hsflowd to send to the designated collectors, either:

  • Use DNS service discovery (DNS-SD)

  • Manually configure the /etc/hsflowd.conf file

Configure sFlow via DNS-SD

You can configure your DNS zone to advertise the collectors and polling information to all interested clients.

Add the following content to the zone file on your DNS server:

_sflow._udp SRV 0 0 6343 collector1
_sflow._udp SRV 0 0 6344 collector2
_sflow._udp TXT (
"txtvers=1"
"sampling.100M=100"
"sampling.1G=1000"
"sampling.10G=10000"
"sampling.40G=40000"
"sampling.100G=100000"
"polling=20"
)

The above snippet instructs hsflowd to send sFlow data to collector1 on port 6343 and to collector2 on port 6344. hsflowd will poll counters every 20 seconds and sample 1 out of every 2048 packets.

The maximum samples per second delivered from the hardware is limited to 16K. You can configure the number of samples per second in the /etc/cumulus/datapath/traffic.conf file, as shown below:

# Set sflow/sample ingress cpu packet rate and burst in packets/sec
# Values: {0..16384}
#sflow.rate = 16384
#sflow.burst = 16384

Start the sFlow daemon:

cumulus@switch:~$ sudo systemctl start hsflowd.service

No additional configuration is required in /etc/hsflowd.conf.

Manually Configure /etc/hsflowd.conf

You can set up the collectors and variables on each switch.

Edit the /etc/hsflowd.conf file to set up your collectors and sampling rates in /etc/hsflowd.conf. For example:

# ====== Sampling/Polling/Collectors ======
  # EITHER: automatic (DNS SRV+TXT from _sflow._udp):
  #   DNS-SD { }
  # OR: manual:
  #   Counter Polling:
  #     polling = 20
  #   default sampling N:
  #     sampling = 400
  #   sampling N on interfaces with ifSpeed:
        sampling.100M = 100
        sampling.1G = 1000
        sampling.10G = 10000
        sampling.40G = 40000
  #   sampling N for apache, nginx:
  #     sampling.http = 50
  #   sampling N for application (requires json):
  #     sampling.app.myapp = 100
  #   collectors:
  collector { ip=192.0.2.100 udpport=6343 }
  collector { ip=192.0.2.200 udpport=6344 }

This configuration polls the counters every 20 seconds, samples 1 of every 2048 packets, and sends this information to a collector at 192.0.2.100 on port 6343 and to another collector at 192.0.2.200 on port 6344.

Some collectors require each source to transmit on a different port, others listen on only one port. Refer to the documentation for your collector for more information.

Configure sFlow Visualization Tools

For information on configuring various sFlow visualization tools, read this Help Center article.