sFlow

sFlow (ver. 5) is a procedure for statistical monitoring of traffic in networks.NVIDIAOnyx supports an sFlow sampling mechanism (agent), which includes collecting traffic samples and data from counters. The sFlow datagrams are then sent to a central collector.

The sampling mechanism must ensure that any packet going into the system has an equal chance of being sampled, irrespective of the flow to which it belongs. The sampling mechanism provides the collector with periodical information on the amount (and load) of traffic per interface by loading the counter samples into sFlow datagrams.

The sFlow packets are encapsulated and sent in UDP over IP. The UDP port number that is used is the standard 6343 by default.

Flow Samples

The sFlow agent samples the data path based on packets.

Truncation and sampling rate are the two parameters that influence the flow samples. In case of congestion the flow samples can be truncated to a predefined size before it is assigned to the CPU. The truncation can be set to any value between 64 to 256 bytes with the default being 128 bytes.

The sampling rate can be adjusted by setting an average rate. The system assures that a random number of packets is sampled, however, the sample rate on average converges to the configured rate. Valid values range between 4000 to 16777215 packets.

The sFlow sends flow samples using an expanded flow sample format.

Statistical Samples

The sFlow agent samples interface counters time based. Polling interval is configurable to any value between 5-3600 seconds with the default being 20 seconds.

The sFlow sends statistical samples using an expanded counter sample format.

The following statistics are gathered by the CPU:

Counter	Description
Total packets	The number of packets that pass through sFlow-enabled ports
Number of flow samples	The number of packets that are captured by the sampling mechanism
Number of statistic samples	The number of statistical samples
Number of discarded samples	The number of samples that were discarded
Number of datagrams	The number of datagrams that were sent to the collector

sFlow Datagrams

The sFlow datagrams contain flow samples and statistical samples.

The sFlow mechanism uses IP protocol, therefore if the packet length is more than the interface MTU, it becomes fragmented by the IP stack. The MTU may also be set manually to anything in the range of 200-9216 bytes. The default is 1400 bytes.

Sampled Interfaces

sFlow must be enabled on physical or LAG interfaces that require sampling. When adding a port to a LAG, sFlow must be disabled on the port. If a port with enabled sFlow is configured to be added to a LAG, the configuration is rejected. Removing a port from a LAG disables sFlow on the port regardless of the LAG’s sFlow status.

Configuring sFlow

Unlock the sFlow commands.
```
switch (config) # protocol sflow
```
Enable sFlow on the system.
```
switch (config) # sflow enable
```

Enter sFlow configuration mode.

switch (config) # sflow
switch (config sflow) #

Set the central collector’s IP.

switch (config sflow) # collector-ip 10.10.10.10

Set the agent-ip used in the sFlow header.

switch (config sflow) # agent-ip 20.20.20.20

(Optional) Set the sampling rate of the mechanism.
```
switch (config sflow) # sampling-rate 16000
```
This means that one every 16000 packet gets collected for sampling.
(Optional) Set the maximum size of the data path sample.
```
switch (config sflow) # max-sample-size 156
```
(Optional) Set the frequency in which counters are polled.
```
switch (config sflow) # counter-poll-interval 19
```
(Optional) Set the maximum size of the datagrams sent to the central collector.
```
switch (config sflow) # max-datagram-size 1500
```

Enable the sFlow agent on the desired interfaces.

switch (config interface ethernet 1/1)# sflow enable
switch (config interface port-channel 1)# sflow enable

Verifying sFlow

To verify the attributes of the sFlow agent:

switch (config)# show sflow
sflow protocol: enabled
sflow: enabled
sampling-rate: 16000
max-sampled-size: 156
counter-poll-interval: 19
max-datagram-size: 1500
collector-ip: 10.10.10.10
collector-port: 6343
agent-ip: 20.20.20.20

ingress ports:
Interfaces:
Ethernet: eth1/1
Port-channel: po1

Statistics:
Total Samples: 2000
Number of flow samples: 1200
Estimated Number of flow discarded: 0
Number of statistic samples: 800
Number of datagrams: 300

Additional Reading and Use Cases

For more information about this feature and its potential applications, please refer to the following community post:

HowTo Configure sFlow on NVIDIA Switches

sFlow Commands

protocol sflow

	protocol sflow no protocol sflow Unhides the sFlow commands. The no form of the command deletes sFlow configuration and hides the sFlow commands.
Syntax Description	N/A
Default	Disabled
Configuration Mode	config
History	3.3.3500
Example	switch (config) # protocol sflow
Related Commands
Notes

sflow enable (global)

	sflow enable no sflow enable Enables sFlow in the system. The no form of the command disables sFlow without deleting the configuration.
Syntax Description	N/A
Default	Disabled
Configuration Mode	config
History	3.3.3500
Example	switch (config) # sflow enable
Related Commands
Notes

	sflow Enters sFlow configuration mode.
Syntax Description	N/A
Default	N/A
Configuration Mode	config
History	3.3.3500
Example	switch (config) # sflowswitch (config sflow) #
Related Commands
Notes

sampling-rate

	sampling-rate <rate> no sampling-rate Configures sFlow sampling ratio. The no form of the command resets this parameter to its default value.
Syntax Description	rate	Configures the number of packets passed before selecting one for sampling Range: 4000-16777215 “0” disables sampling
Default	N/A
Configuration Mode	config
History	3.3.3500
Example	switch (config) # protocol sflow
Related Commands
Notes

max-sample-size

	max-sample-size <packet-size> no max-sample-size Configures the maximum size of sampled packets by sFlow. The no form of the command resets the parameter to its default value.
Syntax Description	packet-size	The sampled packet size Range: 64-256 bytes
Default	N/A
Configuration Mode	config
History	3.3.3500
Example	switch (config sflow) # max-sample-size 165
Related Commands
Notes	Sampled payload beyond the configured size is discarded

counter-poll-interval

	counter-poll-interval <seconds> no counter-poll-interval Configures the sFlow statistics polling interval. The no form of the command resets the parameter to its default value.
Syntax Description	seconds	The sFlow statistics polling interval in seconds Range: 5-3600 seconds; “0” disables the statistic polling
Default	20 seconds
Configuration Mode	config
History	3.3.3500
Example	switch (config sflow) # counter-poll-interval 30
Related Commands
Notes

max-datagram-size

	max-datagram-size <packet-size> no max-datagram-size Configures the maximum sFlow packet size to be sent to the collector. The no form of the command resets the parameter to its default value.
Syntax Description	packet-size	The packet size of the packet being sent to the collector Range: 200-9216 bytes
Default	1400 bytes
Configuration Mode	config
History	3.3.3500
Example	switch (config sflow) # max-datagram-size 9216
Related Commands
Notes	This packet contains the data sample as well as the statistical counter data

collector-ip

	collector-ip <ip-address> [udp-port <udp-port-number>] no collector-ip [<ip-address> udp-port] Configures the collector’s IP. The no form of the command resets the parameters to their default values.
Syntax Description	ip-address	The collector IP address
	udp-port	Configures the collector UDP port number
Default	ip-address: 0.0.0.0 udf-port-number: 6343
Configuration Mode	config
History	3.3.3500
Example	switch (config sflow) # collector-ip 10.10.10.10
Related Commands
Notes

agent-ip

	agent-ip {<ip-address> \| interface [ethernet <slot/port> \| port-channel <channel-group>] \| <if-name> \| loopback <number> \| vlan <id>} no agent-ip Configures the IP address associated with this agent. The no form of the command resets the parameters to their default values.
Syntax Description	interface	Configures a specific Ethernet/LAG interface’s agent IP
	if-name	Interface name (e.g. mgmt0, mgmt1)
	ip-address	The sFlow agent’s IP address (i.e. the source IP of the packet)
	loopback	Loopback interface number Range: 1-32
	vlan	Interface VLAN Range: 1-4094
Default	ip-address: 0.0.0.0
Configuration Mode	config
History	3.3.3500
History	3.3.5200	Updated “interface” parameters
Example	switch (config sflow) # agent-ip 20.20.20.20
Related Commands
Notes	The IP address here is used in the sFlow header

clear counters

	clear counters Clears sFlow counters.
Syntax Description	N/A
Default	N/A
Configuration Mode	config
History	3.3.3500
Example	switch (config sflow) # clear counters
Related Commands
Notes

sflow enable (interface)

	sflow enable no sflow enable Enables sFlow on this interface. The no form of the command disables sFlow on the interface.
Syntax Description	N/A
Default	disable no view-port-channel member
Configuration Mode	config interface ethernet config interface port-channel config interface mlag-port-channel
History	3.3.3500
	3.3.4500	Added MPO configuration mode
Example	switch (config interface ethernet 1/1)# sflow enable
Related Commands
Notes

show sflow

	show sflow Displays sFlow configuration and counters.
Syntax Description	N/A
Default	N/A
Configuration Mode	Any command mode
History	3.3.3500
	3.6.3004	Updated example
	3.6.6000	Updated example
	3.9.2000	Updated example, adding VRF field
Example	switch (config)# show sflow sflow protocol: enabled sflow: enabledVRF name: mgmt sampling-rate: 16000 max-sample-size: 128 counter-poll-interval: 20 max-datagram-size: 1400 ip-agent: 0.0.0.0 ingress ports: Interfaces: Ethernet eth1/2 eth1/1 Statistics: Total Samples: 0 Number of flow samples: 0 Estimated Number of flow discarded: 0 Number of flow statistics samples: 0 Number of datagrams: 0
Related Commands
Notes

Last updated: April 17, 2024