Sflow; Overview; Important Points To Remember - Dell Force10 MXL Blade Reference Manual

sFlow

Overview

The Dell Force10 operating software (FTOS) sFlow monitoring system includes an sFlow agent and an
sFlow collector.
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Important Points to Remember

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The sFlow agent combines the flow samples and interface counters into sFlow datagrams and
forwards them to the sFlow collector.
The sFlow collector analyses the sFlow datagrams received from the different devices and
produces a network-wide view of traffic flows.
FTOS exports all sFlow packets to the sFlow collector. A small sampling rate can equate to a large
number of exported packets. A backoff mechanism is automatically applied to reduce this amount.
Some sampled packets may be dropped when the exported packet rate is high and the backoff
mechanism is about to or is starting to take effect. The dropEvent counter, in the sFlow packet, is
always zero.
sFlow sampling is done on a per-port basis.
Community list and local preference fields are not filled up in the extended gateway element in the
sFlow datagram.
The 802.1P source priority field is not filled up in the extended switch element in the sFlow
datagram.
Only Destination and Destination Peer AS numbers are packed in the dst-as-path field in the
extended gateway element.
If the packet being sampled is redirected using policy-based routing (PBR), the sFlow datagram
may contain incorrect extended gateway/router information.
The source virtual local area network (VLAN) field in the extended switch element is not packed
in case of a routed packet.
The destination VLAN field in the extended switch element is not packed in case of a multicast
packet.
The maximum number of packets that can be sampled and processed per second is:
— 7500 packets when no extended information packing is enabled
— 7500 packets when only extended-switch information packing is enabled (refer to
extended-switch enable)
— 1600 packets when extended-router and/or extended-gateway information packing is enabled
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