sFlow

sFlow is used to monitor data traffic flows traversing different points in a network. The sFlow functionality uses an sFlow agent and an sFlow collector. The agent is software that runs on a network element and samples and reports flow headers and statistics. The collector is software that typically runs on a remote server and receives the flow headers and statistics from one or more sFlow agents.

Sampling and reporting is accomplished as the sFlow agent running on a network element takes periodic samples of ingress traffic and reports the data to one or more collectors. The network element does not need to maintain a local flow cache. Instead, the sampled header information is immediately sent to the collector without additional processing.

The SR Linux supports sFlow version 5 behavior and formats. On 7250 IXR chassis-based systems, sFlow is implemented in hardware. On 7220 IXR systems, sFlow functionality is implemented in software. sFlow behavior is identical on both platforms.

sFlow sampling

sFlow works by sampling flow data and reporting the samples to the configured sFlow collectors. Based on the configured system sampling rate, the forwarding plane samples ingress packet flows and sends the sampled headers to the sFlow agent in the control plane.

All ingress packets are subject to sampling. Each sample includes the top 256 bytes of the sampled packet, starting at the outer Ethernet header. The sampled packets are sent to the configured sFlow collectors with the sampled data in sFlow raw packet data format.

For sampled IPv4 packets, the IPv4 header data fields are sent with the raw data. For sampled IPv6 packets, the IPv6 header data fields are sent with the raw data.

sFlow collector reporting

sFlow reports sampled headers and statistics to the configured collectors using IP/UDP datagrams. UDP port 6343 is the default destination port, but you can optionally configure a different port. Sampled packets are sent as soon as the samples are taken, and interface statistics are sent at 10 second intervals. SR Linux supports up to 8 remote sFlow collectors. Each collector can only have one IPv4 address. The flow and counter samples are aggregated in a sflow datagram packet in software implementation.

sFlow counter samples

Another aspect of the sFlow agent is streaming of interface statistics to configured sFlow collectors. Statistics are only sent to a collector if sFlow has been enabled on an interface. Interface statistics are sent based on a default poll-interval of 10 seconds with a separate timer for each interface. When the interval expires. the current value of each associated statistics are sent to the configured collectors.

The interface counter sample contains:

  • Interface index

  • Interface type

  • Interface speed

  • Oper and admin status

  • Input octets

  • Input packets

  • Input broadcast packets

  • Input discards packets

  • Output errors

  • Output octets

  • Output packets

  • Output broadcast packets

  • Output discards packets

Configuring the sFlow agent

To configure the sFlow agent on the system, you enable sFlow, and optionally configure the sampling rate (by default, 1 out of every 10,000 packets) and sample size (by default, 256 bytes are sampled from each packet).

Configuring the sFlow agent

The following example enables sFlow on the system and configures the system sampling rate and sample size. Note that the sample size and polling interval are not configurable. The following default sample size applies:

  • 7220 IXR-D2, D3, D4, D5, and 7220 IXR-H systems: 256 bytes

  • 7250 IXR 6/10: 220 bytes

--{ * candidate shared }--[  ]--
    system {
        sflow {
            admin-state enable
            }
        }
    }

Configuring sFlow collectors

The sFlow agent sends sampled packets to sFlow collectors. You can configure up to 8 sFlow collectors to receive the data. To configure an sFlow collector, you specify its IP address, associated network instance, and IP address to be used as the source IP address in sFlow packets sent from the SR Linux to the collector. You can optionally specify a destination port (by default, this is UDP port 6343).

Note:

Configuring a network-instance is mandatory. Also, a collector cannot be reached using the mgmt network-instance.

Configuring sFlow collectors

The following example configures two sFlow collectors. The IP address for each collector is configured, as well as its network instance and source IP address. Each collector receives all samples.

--{ * candidate shared }--[  ]--
    system {
        sflow {
            collector 1 {
                collector-address 10.50.4.1
                source-address 192.0.2.1
                network-instance default
            collector 2 {
                collector-address 10.50.4.2
                source-address 10.1.5.2
                network-instance default
                port 4310
                }
            }
        }
    }

Configuring sFlow for an interface

When sFlow is configured for an interface, the ingress packets are taken for sampling according to the sample-rate.

Configuring sFlow for an interface

The following example enables sFlow on an interface.

--{ * candidate shared }--[  ]--
    interface ethernet-1/1 {
        sflow {
            admin-state enable
        }
    }

Displaying the state of the sFlow agent

To display the system-wide state of the sFlow agent, including any sFlow parameters, collector configuration, and general statistics, use the info from state command in candidate or running mode, or the info command in state mode.

Info from state command

# info from state system sflow
    system {
        sflow {
            admin-state enable
            sample-rate 1000
            sample-size 256
            collector 1 {
                collector-address 10.1.1.24
                network-instance default
                source-address 10.0.0.1
                port 6343
                next-hop 172.24.71.65
            }
            statistics {
                total-samples-taken 5457
                total-sent-packets 26800
            }
        }
    }

Displaying the status of the sFlow agent

Use the show system sflow status command in show mode to display the general status of the sFlow agent:

Show system sflow status command

--{ running }--[  ]--
# enter show
# show system sflow status
-------------------------------------
Admin State            : enable
Sample Rate            : 10000
Sample Size            : 256
Total Samples          : 0
Total Collector Packets: 3269158
-------------------------------------
collector-id     : 8
collector-address: 172.10.10.10
network-instance : default
source-address   : 10.0.0.1
port             : 6343
next-hop         : 172.24.71.65
-------------------------------------

sFlow formats

Raw packet header shows an example of a raw packet header for an sFlow format.

Figure 1. Raw packet header

Sampled data and counter examples

The following is an example of sample data:

Flow sample data

InMon sFlow
    Datagram version: 5
    Agent address type: IPv4 (1)
    Agent address: 10.0.0.1
    Sub-agent ID: 2
    Sequence number: 0
    SysUptime: 0
    NumSamples: 1
    Flow sample, seq 0
        0000 0000 0000 0000 0000 .... .... .... = Enterprise: standard sFlow (0)
        .... .... .... .... .... 0000 0000 0001 = sFlow sample type: Flow sample (1)
        Sample length (byte): 141
        Sequence number: 0
        0000 0000 .... .... .... .... .... .... = Source ID class: 0
        .... .... 0000 0000 0000 0000 0011 0110 = Index: 54
        Sampling rate: 1 out of 5 packets
        Sample pool: 0 total packets
        Dropped packets: 0
        Input interface (ifIndex): 54
        .000 0000 0000 0000 0000 0000 0011 0110 = Output interface (ifIndex): 54
        Flow record: 1
        Raw packet header
            0000 0000 0000 0000 0000 .... .... .... = Enterprise: standard sFlow (0)
            Format: Raw packet header (1)
            Flow data length (byte): 101
            Header protocol: Ethernet (1)
            Frame Length: 98
            Payload removed: 0
            Original packet length: 85
            Header of sampled packet: 
                000c00020000000000111111080045000052000000004006...
                Ethernet II, Src: 00:00:00_11:11:11 (00:00:00:11:11:11), 
                    Dst: BebIndus_02:00:00 (00:0c:00:02:00:00)
                    Destination: BebIndus_02:00:00 (00:0c:00:02:00:00)
                    Source: 00:00:00_11:11:11 (00:00:00:11:11:11)
                    Type: IPv4 (0x0800)
                Internet Protocol Version 4, Src: 10.100.1.2, Dst: 10.1.1.2
                    0100 .... = Version: 4
                    .... 0101 = Header Length: 20 bytes (5)
                    Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
                    Total Length: 82
                    Identification: 0x0000 (0)
                    Flags: 0x00
                    Fragment offset: 0
                    Time to live: 64
                    Protocol: TCP (6)
                    Header checksum: 0x35a1 [validation disabled]
                    [Header checksum status: Unverified]
                    Source: 10.100.1.2
                    Destination: 10.1.1.254
                    [Source GeoIP: Unknown]
                    [Destination GeoIP: Unknown]
                Transmission Control Protocol, Src Port: 0, Dst Port: 0, Seq: 0
                LBT-TCP Protocol
                LBMC Protocol
                [Unreassembled Packet: LBT-TCP]

The following is a counter sample example:

Counters sample

InMon sFlow
    Datagram version: 5
    Agent address: 10.0.0.1 (10.0.0.1)
    Sub-agent ID: 0
    Sequence number: 8
    SysUptime: 6548000
    NumSamples: 1
    Counters sample, seq 1
        Enterprise: standard sFlow (0)
        sFlow sample type: Counters sample (2)
        Sample length (byte): 108
        Sequence number: 1
        Source ID type: 64
        Source ID index: 49150
        Counters records: 1
        Generic interface counters
            Enterprise: standard sFlow (0)
            Format: Generic interface counters (1)
            Flow data length (byte): 88
            Interface index: 1073790974
            Interface Type: 6
            Interface Speed: 25600
            IfDirection: Full-Duplex
            IfAdminStatus: Up
            IfOperStatus: Up
            Input Octets: 0
            Input Packets: 0
            Input Multicast Packets: 0
            Input Broadcast Packets: 0
            Input Discarded Packets: 0
            Input Errors: 0
            Input Unknown Protocol 
        Packets: 0
            Output Octets: 0
            Output Packets: 0
            Output Multicast Packets: 0
            Output Broadcast Packets: 0
            Output Discarded Packets: 0
            Output Errors: 0
            Promiscuous Mode: 0