Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual page 3938

Complete Software Guide for Junos
3834
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OS for EX Series Ethernet Switches, Release 10.4
the switch to send copies of unicast traffic to either a local analyzer port or an analyzer
VLAN. Then you can analyze the mirrored traffic using a protocol analyzer application.
The protocol analyzer application can run either on a computer connected to the analyzer
output interface or on a remote monitoring station.
We recommend that you disable port mirroring when you are not using it and that you
select specific interfaces as input to the port mirror analyzer in preference to using the
all keyword option. You can also limit the amount of mirrored traffic by using statistical
sampling, setting a ratio to select a statistical sample, or using a firewall filter. Mirroring
only the necessary packets reduces any potential performance impact.
With local port mirroring, traffic from multiple ports is replicated to the analyzer output
interface. If the output interface for an analyzer reaches capacity, packets are dropped.
You should consider whether the traffic being mirrored exceeds the capacity of the
analyzer output interface.
You can use port mirroring on a switch to mirror any of the following:
Packets entering or exiting a port—You can mirror the packets in any combination
(on up to 256 ports). For example, you can send copies of the packets entering some
ports and the packets exiting other ports to the same local analyzer port or analyzer
VLAN.
Packets entering a VLAN on an EX2200, EX3200, EX4200, or EX4500 switch—You
can mirror the packets entering a VLAN on these switches to either a local analyzer
port or to an analyzer VLAN. (On EX3200, EX4200, and EX4500 switches, you can
configure multiple VLANs [up to 256 VLANs], including a VLAN range and PVLANs, as
ingress input to an analyzer.)
Packets exiting a VLAN on an EX8200 switch—You can mirror the packets exiting a
VLAN on an EX8200 switch to either a local analyzer port or to an analyzer VLAN. You
can configure multiple VLANs (up to 256 VLANs), including a VLAN range and PVLANs,
as egress input to an analyzer.
Statistical sample—You can mirror a statistical sample of packets that are
Entering or exiting a port
Entering a VLAN on an EX2200, EX3200, EX4200, or EX4500 switch
Exiting a VLAN on an EX8200 switch
You specify the sample number of packets by setting the ratio. You can send the sample
to either a local analyzer port or to an analyzer VLAN.
Policy-based sample—You can mirror a policy-based sample of packets that are
entering a port or a VLAN. You configure a firewall filter to establish a policy to select
certain packets. You can send the sample to a local analyzer port or to an analyzer
VLAN.
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