Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 920)

890 Multi-Service IronWare Switching Configuration Guide
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sFlow event workflow
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Sampling rate
The sampling rate is the average ratio of the number of packets incoming on an sFlow-enabled
port, to the number of flow samples taken from those packets. Device ports send only the sampled
traffic to the CPU. sFlow sampling requires high LP CPU usage, which can affect performance in
some configurations, especially if a high sampling rate is implemented.
Configured rate and actual rate
When you enter a sampling rate value, this value is the configured rate. The software rounds the
value you enter to the next higher odd power of 2 to obtain the actual rate. This value becomes the
actual sampling rate. For example, if the configured sampling rate is 1000, then the actual rate is
2048; and the hardware samples 1 in 2048 packets.
NOTE
This behavior applies to the Brocade NetIron XMR and Brocade MLX Series platforms and does not
apply to the Brocade NetIron CES and Brocade NetIron CER devices. In Brocade NetIron CES and
Brocade NetIron CER devices, the system does not apply rounding.
Extended router information
Extended router information contains information for the next hop router. This information includes
the next hop router’s IP address and the outgoing VLAN ID. Extended router information also
includes the source IP address prefix length and the destination IP address prefix length.
The prefix length of IPv4 source and destination IP addresses is collected only if you configure BGP
on the devices.
Extended gateway information
Extended gateway information is included in an sFlow sampled packet if BGP is enabled. The
extended gateway information includes the following BGP information about the packet’s
destination route:
• This router’s autonomous system (AS) number
• The route’s source IP AS number
• The route’s source peer AS number
• The AS path to the destination
In BGP-configured routers, AS Path information is collected from each node traversed by the sFlow
packets.
NOTE
AS communities and local preferences are not included in the sampled packets.
To obtain extended gateway information, use “struct extended_gateway” as described in RFC 3176
sFlow null0 sampling
This feature allows Brocade devices to sample null0 dropped packets. This is useful in cases such
as DOS attack on a particular route.