Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - IP SERVICES CONFIGURATION GUIDE 2010-10-01 Configuration Manual page 122

JunosE 11.3.x IP Services Configuration Guide
ip flow-sampling-mode packet-interval
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at the specified packet interval. You can specify an interval in the range 1–4,000,000,000
packets.
When you use the ip flow-sampling-mode packet-interval command to define the
packet-sampling interval for Gigabit Ethernet interfaces configured on the ES2 10G LM
(line module) with either the ES2-S1 GE-8 IOA or the ES2-S2 10GE PR IOA on E120 routers
and E320 routers, the J-Flow application makes the following internal adjustments to
achieve better performance on the ES2 10G LM, regardless of the packet-sampling interval
that you configure:
J-Flow adjusts the maximum sampling interval to 8,388,608, which is the decimal
equivalent of 0x800000.
J-Flow changes the packet-sampling value to the closest integer that is a power of
two and that is less than or equal to the configured value.
For performance reasons, J-Flow applies these adjustments to the sampling interval only
for the interfaces configured on the ES2 10G LM on the virtual router. The configured
sampling interval does not change for interfaces not configured on the ES2 10G LM on
the virtual router.
When the data rate increases on a given interface, J-Flow packet sampling might not be
able to maintain the configured sampling rate and might drop the intended sampled
packets. If this occurs, you can address the issue by reducing the sampling rate.
NOTE: For all modules except the ES2 10G LM on the E120 router and the
E320 router, packet sampling occurs individually for each processor. Because
the router distributes packets over multiple processors, sampling occurs
when each processor reaches the specified packet interval.
Even though each flow is sampled, the flow sample is not necessarily cached
because of system constraints.
Use to define the J-Flow packet-sampling interval.
Specify a packet-sampling interval in the range 1–4000000000 packets; the default
value is 4000000000.
Specifying an interval less than 10 sets a very high sampling rate that can severely
degrade performance. The lower the packet-sampling interval you configure, the faster
the sampling rate.
For information about the effects of using the ip flow-sampling-mode packet-interval
command for the ES2 10G LM with either the ES2-S1 GE-8 IOA or the ES2-S2 10GE PR
IOA on E120 routers and E320 routers, see "Defining a Sampling Interval" on page 95 .
Example—Samples 1 out of 50 packets from the line module on which the interface
resides
host1(config)#ip flow-sampling-mode packet-interval 50
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