Defining A Sampling Interval - Juniper IP SERVICES - CONFIGURATION GUIDE V 11.1.X Configuration Manual

JUNOSe 11.1.x IP Services Configuration Guide

Defining a Sampling Interval

Use the ip flow-sampling-mode packet-interval command to define the
packet-sampling interval for the virtual router. The sampling interval specifies the
rate at which the virtual router samples J-Flow information. This rate is used for all
interfaces that have J-Flow enabled. After you enable J-Flow on an interface, the
virtual router samples one packet 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:
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.
ip flow-sampling-mode packet-interval
100
Configuring Flow-Based Statistics Collection
Use the no version to disable J-Flow statistics on the interface.
See ip route-cache flow sampled.
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.
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.