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 daemon that samples and sends sFlow data to configured collectors. hsflowd is not included in the base Cumulus Linux installation. After installation, hsflowd will automatically start when the switch boots up.

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Installing hsflowd

To download and install the  hsflowd package, use apt-get:

cumulus@switch:~$ sudo apt-get update
cumulus@switch:~$ sudo apt-get install -y hsflowd

Configuring sFlow

You can configure hsflowd to send to the designated collectors via two methods:

  • DNS service discovery (DNS-SD)
  • Manually configuring /etc/hsflowd.conf

Configuring sFlow via DNS-SD

With this method, you need to 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.1G=2048"
"sampling.10G=4096"
"sampling.40G=8192"
"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.

From Cumulus Linux 2.5.3 onwards, the maximum samples/second delivered from the hardware is limited to 16K. This can be configured by editing 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

After the initial configuration is ready, bring up the sFlow daemon by running:

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

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

Manually Configuring /etc/hsflowd.conf

With this method you will set up the collectors and variables on each switch.

Edit /etc/hsflowd.conf and change DNSSD = on to DNSSD = off:

DNSSD = off

Then set up your collectors and sampling rates in /etc/hsflowd.conf:

# Manual Configuration (requires DNSSD=off above)
  #################################################

  # Typical configuration is to send every 30 seconds
  polling = 20

  sampling.1G=2048
  sampling.10G=4096
  sampling.40G=8192

  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 may listen on only one port. Please refer to the documentation for your collector for more information.

Configuring sFlow Visualization Tools

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

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