Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.14.1.0 - Page 867
Back-Off Mechanism, sFlow on LAG ports, Enabling Extended sFlow, Back-Off
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Back-Off Mechanism If the sampling rate for an interface is set to a very low value, the CPU can get overloaded with flow samples under high-traffic conditions. In such a scenario, a binary back-off mechanism gets triggered, which doubles the sampling-rate (halves the number of samples per second) for all interfaces. The backoff mechanism continues to double the sampling-rate until the CPU condition is cleared. This is as per sFlow version 5 draft. After the back-off changes the sample-rate, you must manually change the sampling rate to the desired value. As a result of back-off, the actual sampling-rate of an interface may differ from its configured sampling rate. You can view the actual sampling-rate of the interface and the configured sample-rate by using the show sflow command. sFlow on LAG ports When a physical port becomes a member of a LAG, it inherits the sFlow configuration from the LAG port. Enabling Extended sFlow Extended sFlow packs additional information in the sFlow datagram depend on the type of sampled packet. The platform supports extended-switch information processing only. Extended sFlow packs additional information in the sFlow datagram depending on the type of sampled packet. You can enable the following options: • extended-switch - 802.1Q VLAN ID and 802.1p priority information. • extended-router - Next-hop and source and destination mask length. • extended-gateway - Source and destination AS number and the BGP next-hop. NOTE: The entire AS path is not included. BGP community-list and local preference information are not included. These fields are assigned default values and are not interpreted by the collector. • Enable extended sFlow. sflow [extended-switch] [extended-router] [extended-gateway] enable By default packing of any of the extended information in the datagram is disabled. • Confirm that extended information packing is enabled. show sflow Examples of Verifying Extended sFlow The bold line shows that extended sFlow settings are enabled on all three types. DellEMC#show sflow sFlow services are enabled Egress Management Interface sFlow services are disabled Global default sampling rate: 32768 Global default counter polling interval: 20 Global default extended maximum header size: 128 bytes Global extended information enabled: none 1 collectors configured Collector IP addr: 100.1.1.1, Agent IP addr: 1.1.1.2, UDP port: 6343 VRF: Default 0 UDP packets exported 0 UDP packets dropped 0 sFlow samples collected stack-unit 0 Port set 0 Te 1/1: configured rate 16384, actual rate 16384 DellEMC# If you did not enable any extended information, the show output displays the following (shown in bold). DellEMC#show sflow sFlow services are disabled sFlow 867
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