Optimizing Packet Mirroring Performance; Determine Traffic Loads; Establish Resource Guidelines - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - POLICY MANAGEMENT CONFIGURATION GUIDE 2010-10-04 Configuration Manual

JunosE 11.3.x Policy Management Configuration Guide
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Optimizing Packet Mirroring Performance

Determine Traffic Loads

Establish Resource Guidelines

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If the packet mirroring request is a RADIUS-initiated session (a RADIUS-based packet
mirroring session for a subscriber who is already logged in), the router verifies the validity
of all of the mirroring rules related to the particular subscriber. If any of the rules fail (for
example, the identification fields do not match), the packet mirroring request is denied.
The calling-station-id trigger is externally visible only for tunneled users (if there are no
RADIUS overrides). If a case-sensitive user name does not match a subscriber's name
or if the dynamic IP interface UID does not exist, the subscriber is disregarded.
Avoiding Conflicts Between Multiple Packet Mirroring Configurations on page 241
Packet mirroring operations require some system resources. As a general rule, to avoid
performance degradation, limit the amount of mirrored traffic to a maximum of 5 percent
of the E Series router's total traffic.
For many packet mirroring environments, using the 5-percent guideline is sufficient.
However, if you want to more closely manage packet mirroring's use of your router's
resources, this section provides guidelines and equations to help you determine your
packet mirroring requirements.
The guidelines for packet mirroring requirements use the following assumptions for a
specific line module:
A = Total input traffic at the line module
B = Total output traffic at the line module
X = Amount of traffic mirrored at input in the line module
Y = Amount of traffic mirrored at output in the line module
Using the previous assumptions, you can determine traffic loads for a given line module:
A = Load at ingress side of the line module
(B + X) = Load at egress side of the line module
(A + 2X + Y) = Load at ingress to fabric from the line module
Next, using the traffic loads that you determined for the line module, you can establish
guidelines for the amount of packet mirroring traffic for your router.
If you exceed these guidelines, regular (non-packet mirroring) packets from all subscribers,
including nonmirrored subscribers, will be dropped. If the fabric bandwidth is not exceeded,
then the performance penalties are contained within the slot where the packet mirroring
activity occurs. However, if the fabric bandwidth is exceeded, traffic from other line
modules might also be dropped.
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