When sFlow is enabled on an SR OS router, the system takes upon a role of an sFlow network device as described in sFlow protocol version 5. A single sFlow agent can be configured for counter polling (flow sampling is not supported). There is no support for sub-agents.
The sFlow agent sends sFlow data to an operator-configured sFlow receiver. A single receiver is supported with configurable primary and backup IPv4 or IPv6 UDP destination sockets for redundancy (each sFlow packet exported is duplicated to both sockets when both are configured). The receiver's UDP sockets can be reachable either in-band or out-of-band (default) and must both be IPv4 or IPv6. An operator can also set the maximum size of the sFlow datagrams. Operators are expected to set this value to avoid IP fragmentation (Datagrams exceeding the specified size are fragmented before handed to IP layer).
The sFlow agent manages all sFlow data sources in the system. SR OS supports sFlow data that are physical ports. When a port is configured as an sFlow data source, counters for that port and all VPLS and Epipe SAPs on that port are collected and exported using sFlow (see later on section for record format). Flow data sources can only be configured when an sFlow receiver is configured. To remove the sFlow receiver, all sFlow data sources must first be deconfigured at the port level.
Each data source is processed at a 15-second, non-configurable interval. If multiple data sources exist on a line card, the line card distributes the processing of each data source within a 15 second interval to avoid sFlow storms. When a timer expires to trigger a data source processing, data is collected for the physical port and for all VLL and VPLS SAPs on that port and exported using sFlow version 5 records as described in later subsections of this document. Each port and all SAP records for a data source for a specific interval are collected and sent with the counter sequence number and the timestamp value (the time value corresponds to the time counters were actually collected by a line card). The timestamp value uses line card's sysUptime value, which is synchronized with CPM time automatically by the system. A line card sends the counters to a CPM card, where sFlow UDP datagrams are created, sequenced with the CPM sequence number and sent to the receiver. If no UDP sockets are configured, no errors are generated because data is not sent. If no UDP sockets are reachable, the created UDP sFlow datagrams are dropped.
The card hard or soft resets.
The MDA resets.
The sFlow agent counter map changes.
The CPM resets the sFlow datagram sequence numbers if, as a result of configuration or operational change, the sFlow datagram to be sent no longer provides continuity with the previous datagram. The following lists examples of when this takes place:
HA switch
CTL reboot
creation of an sFlow receiver