12-Network Management and Monitoring Configuration Guide

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11-sFlow configuration
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Configuring sFlow

sFlow is a traffic monitoring technology.

As shown in Figure 1, the sFlow system involves an sFlow agent embedded in a device and a remote sFlow collector. The sFlow agent collects interface counter information and packet information and encapsulates the sampled information in sFlow packets. When the sFlow packet buffer is full, or the aging timer (fixed to 1 second) expires, the sFlow agent performs the following actions:

·     Encapsulates the sFlow packets in the UDP datagrams.

·     Sends the UDP datagrams to the specified sFlow collector.

The sFlow collector analyzes the information and displays the results. One sFlow collector can monitor multiple sFlow agents.

sFlow provides the following sampling mechanisms:

·     Flow samplingObtains packet information.

·     Counter sampling—Obtains interface counter information.

Figure 1 sFlow system

 

Protocols and standards

·     RFC 3176, InMon Corporation's sFlow: A Method for Monitoring Traffic in Switched and Routed Networks

·     sFlow.org, sFlow Version 5

Configuration restrictions and guidelines

When you configure sFlow in an EVPN network, you must specify the source IP address of sFlow packets by using the sflow source command. For information about EVPN, see EVPN Configuration Guide.

sFlow configuration task list

Tasks at a glance

(Required.) Configuring the sFlow agent and sFlow collector information

Perform at least one of the following tasks:

·     Configuring flow sampling

·     Configuring counter sampling

 

Configuring the sFlow agent and sFlow collector information

Step

Command

Remarks

1.     Enter system view.

system-view

N/A

2.     (Optional.) Configure an IP address for the sFlow agent.

sflow agent { ip ip-address | ipv6 ipv6-address }

By default, no IP address is configured for the sFlow agent. The switch periodically checks whether the sFlow agent has an IP address. If not, the switch automatically selects an IPv4 address for the sFlow agent but does not save the IPv4 address in the configuration file.

NOTE:

·     As a best practice, manually configure an IP address for the sFlow agent.

·     Only one IP address can be configured for the sFlow agent on the switch, and a newly configured IP address overwrites the existing one.

3.     Configure the sFlow collector information.

sflow collector collector-id [ vpn-instance vpn-instance-name ] { ip ip-address | ipv6 ipv6-address } [ port port-number | datagram-size size | time-out seconds | description text ] *

By default, no sFlow collector information is configured.

The value range for the collector-id argument is 1 to 10.

4.     (Optional.) Specify the source IP address of sFlow packets.

sflow source { ip ip-address | ipv6 ipv6-address } *

By default, the source IP address is determined by routing.

 

Configuring flow sampling

Perform this task to configure flow sampling on an Ethernet interface. The sFlow agent performs the following tasks:

1.     Samples packets on that interface according to the configured parameters.

2.     Encapsulates the packets into sFlow packets.

3.     Encapsulates the sFlow packets in the UDP packets and sends the UDP packets to the specified sFlow collector.

To configure flow sampling:

 

Step

Command

Remarks

1.     Enter system view.

system-view

N/A

2.     Enter Layer 2 Ethernet interface view or Layer 3 Ethernet interface view.

interface interface-type interface-number

N/A

3.     (Optional.) Set random flow sampling mode.

sflow sampling-mode random

By default, random sampling is used.

4.     Enable flow sampling and specify the number of packets out of which flow sampling samples a packet on the interface.

sflow sampling-rate rate

By default, flow sampling is disabled.

5.     (Optional.) Set the maximum number of bytes (starting from the packet header) that flow sampling can copy per packet.

sflow flow max-header length

The default setting is 128 bytes.

As a best practice, use the default setting.

6.     Specify the sFlow instance and sFlow collector for flow sampling.

sflow flow [ instance instance-id ] collector collector-id

By default, no sFlow instance or sFlow collector is specified for flow sampling.

 

Configuring counter sampling

Perform this task to configure counter sampling on an Ethernet interface. The sFlow agent performs the following tasks:

1.     Periodically collects the counter information on that interface.

2.     Encapsulates the counter information into sFlow packets.

3.     Encapsulates the sFlow packets in the UDP packets and sends the UDP packets to the specified sFlow collector.

To configure counter sampling:

 

Step

Command

Remarks

1.     Enter system view.

system-view

N/A

2.     Enter Layer 2 Ethernet interface view or Layer 3 Ethernet interface view.

interface interface-type interface-number

N/A

3.     Enable counter sampling and set the counter sampling interval.

sflow counter interval interval-time

By default, counter sampling is disabled.

4.     Specify the sFlow instance and sFlow collector for counter sampling.

sflow counter [ instance instance-id ] collector collector-id

By default, no sFlow instance or sFlow collector is specified for counter sampling.

 

Displaying and maintaining sFlow

Execute display commands in any view.

 

Task

Command

Display sFlow configuration.

display sflow

 

sFlow configuration example

Network requirements

As shown in Figure 2, perform the following tasks:

·     Configure flow sampling in random mode and counter sampling on GigabitEthernet 1/0/1 of the device to monitor traffic on the port.

·     Configure the device to send sampled information in sFlow packets through GigabitEthernet 1/0/3 to the sFlow collector.

Figure 2 Network diagram

 

Configuration procedure

1.     Configure the IP addresses and subnet masks for interfaces, as shown in Figure 2. (Details not shown.)

2.     Configure the sFlow agent and configure information about the sFlow collector:

# Configure the IP address for the sFlow agent.

<Device> system-view

[Device] sflow agent ip 3.3.3.1

# Configure information about the sFlow collector. Specify the sFlow collector ID as 1, IP address as 3.3.3.2, port number as 6343 (default), and description as netserver.

[Device] sflow collector 1 ip 3.3.3.2 description netserver

3.     Configure counter sampling:

# Enable counter sampling and set the counter sampling interval to 120 seconds on GigabitEthernet 1/0/1.

[Device] interface gigabitethernet 1/0/1

[Device-GigabitEthernet1/0/1] sflow counter interval 120

# Specify sFlow collector 1 for counter sampling.

[Device-GigabitEthernet1/0/1] sflow counter collector 1

4.     Configure flow sampling:

# Enable flow sampling and set the flow sampling mode to random and sampling interval to 4000.

[Device-GigabitEthernet1/0/1] sflow sampling-mode random

[Device-GigabitEthernet1/0/1] sflow sampling-rate 4000

# Specify sFlow collector 1 for flow sampling.

[Device-GigabitEthernet1/0/1] sflow flow collector 1

Verifying the configurations

# Verify the following items:

·     GigabitEthernet 1/0/1 enabled with sFlow is active.

·     The counter sampling interval is 120 seconds.

·     The flow sampling interval is 4000 (one packet is sampled from every 4000 packets).

[Device-GigabitEthernet1/0/1] display sflow

sFlow datagram version: 5

Global information:

Agent IP: 3.3.3.1(CLI)

Source address:

Collector information:

ID    IP              Port  Aging      Size VPN-instance Description

1     3.3.3.2         6343  N/A        1400              netserver

Port counter sampling information:

Interface   Instance   CID   Interval(s)

GE1/0/1     1          1     120

Port flow sampling information:

Interface   Instance   FID   MaxHLen Rate       Mode      Status

GE1/0/1     1          1     128     4000       Random    Active

Troubleshooting sFlow configuration

The remote sFlow collector cannot receive sFlow packets

Symptom

The remote sFlow collector cannot receive sFlow packets.

Analysis

The possible reasons include:

·     The sFlow collector is not specified.

·     sFlow is not configured on the interface.

·     The IP address of the sFlow collector specified on the sFlow agent is different from that of the remote sFlow collector.

·     No IP address is configured for the Layer 3 interface that sends sFlow packets.

·     An IP address is configured for the Layer 3 interface that sends sFlow packets. However, the UDP datagrams with this source IP address cannot reach the sFlow collector.

·     The physical link between the device and the sFlow collector fails.

·     The sFlow collector is bound to a non-existent VPN.

·     The length of an sFlow packet is less than the sum of the following two values:

¡     The length of the sFlow packet header.

¡     The number of bytes that flow sampling can copy per packet.

Solution

To resolve the problem:

1.     Use the display sflow command to verify that sFlow is correctly configured.

2.     Verify that a correct IP address is configured for the device to communicate with the sFlow collector.

3.     Verify that the physical link between the device and the sFlow collector is up.

4.     Verify that the VPN bound to the sFlow collector already exists.

5.     Verify that the length of an sFlow packet is greater than the sum of the following two values:

¡     The length of the sFlow packet header.

¡     The number of bytes (as a best practice, use the default) that flow sampling can copy per packet.

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