Egress sFlow Sampling

Egress sFlow sampling functionality extends sampling to the egress traffic, both unicast and multicast streams. When egress sFlow sampling is enabled on a port, the sFlow agent samples the egress traffic on that port, and these sampled packets are processed by slow path passed on to the collector. You can configure the rate at which the packets are sampled.

Both ingress and egress sampling can be enabled simultaneously on a port. The sample-rate is maintained on a per-port basis, so a given port will have the same sample rate for ingress and egress traffic.

This feature supports the following configuration options:

sFlow can sample the egress flow of a physical interface; in this case, the sFlow agent samples the packet from the egress flow of an interface.
sFlow can sample both the ingress and egress flows of an interface; in this case the sFlow agent samples the packet from the ingress and egress flow of a configured interface.

Similar to existing ingress sFlow sampling, the egress sFlow sampling samples both unicast and multicast egress flows. The global enable/disable control of sFlow is common for both ingress and egress. When the global option is enabled, the port level sFlow parameters are applied to hardware.

Limitations

The following list identifies limitations of the egress sFlow feature:

Due to the hardware limitation, destination port information is not supported for multicast traffic. The output interface index is populated as 0.
The egress sFlow sampling does not support de-duplication of packets.
For multicast traffic, the sampling rate, sample pool of the egress sFlow sampled datagram will be populated as 0, because the source ID of the egress sampled multicast packet is unknown.
For L3 unicast traffic, an unmodified packet is sampled and the destination port is supplied if the L3 traffic is a flow within single chip. When the egress port and ingress port are in different chips, then a modified packet is sampled and the destination ports are supplied. For L3 multicast traffic, unmodified packet is sampled and destination port will be populated as zero.
Packets dropped due to egress ACL will be sampled.
In cases of unicast and multicast flooding, the packets are sampled before packet replication. If the ingress and member ports are in the same chip then a single copy of the packet is sampled even though the egress sFlow is enabled on more than one member's ports. If the member ports are spread across different chips, then packets are sampled on a per-chip basis.
In flooding cases, the least configured sampling rate among the member ports on a port group is considered as a sample rate. Even if you configure different sample rates on a member ports, egress sampling is performed based on least configured sample rate among the member ports on a unit.