Juniper JUNOS 10.1 - CONFIGURATION GUIDE 1-2010 Configuration Manual page 292

JUNOS 10.1 Network Interfaces Configuration Guide
NOTE:
Performing DCU accounting when an output service is enabled produces inconsistent
behavior in the following configuration:
For an incoming packet with source and destination prefixes matching the SCU and
DCU classes respectively configured in the router, both SCU and DCU counters will
be incremented. This behavior is not harmful or negative. However, it is inconsistent
with non-serviced packets, in that only the SCU count will be incremented (because
the SCU class ID will override the DCU class ID in this case).
To enable packet counting on an interface, include the
direction
You can include these statements at the following hierarchy levels:
For SCU to work, you must configure at least one input interface and at least one
output interface. An incoming packet is counted only once, and SCU takes priority
over DCU. This means that when a packet arrives on an interface on which you
include the
configuration, and when the source and destination both match accounting prefixes,
the JUNOS Software associates the packet with the source class only. To ensure the
outgoing packet is counted, include the
configuration of the outgoing interface.
222
Enabling Source Class and Destination Class Usage
Both SCU input and DCU are configured on the packet input interface.
SCU output is configured on the packet output interface.
Interface services is enabled on the output interface.
accounting {
destination-class-usage;
source-class-usage {
direction;
}
}
can be one of the following:
—Configure at least one expected ingress point.
input
output —Configure at least one expected egress point.
—On a single interface, configure at least one expected ingress point
input output
and one expected egress point.
[edit interfaces interface-name unit logical-unit-number family (inet | inet6 | mpls)]
[edit logical-systems logical-system-name interfaces interface-name unit
logical-unit-number family (inet | inet6 | mpls)]
source-class-usage input
accounting
and
destination-class-usage
source-class-usage output
statement:
statements in the
statements in the