Juniper POLICY MANAGEMENT - CONFIGURATION GUIDE V11.1.X Configuration Manual page 147

If there is no existing internal parent group with the same name in the merged
policy, the system creates a corresponding internal parent group with the same
name.
If an internal parent group with the same name already exists, the system uses
a name built by appending an internally generated sequence number to the
name of the internal parent group in the component policy.
If the length of the name exceeds the maximum length allowed, the policy merge
fails.
If a classifier group in a component policy refers to an internal parent group, the
same classifier group in the merged policy corresponds to the internal parent
group in the merged policy.
If a classifier group in a component policy refers to an external parent group,
the same classifier group in the merged policy refers to the same external parent
group.
If there is a conflict where two or more component policies contain the same
classifier group referring to an internal parent group in a corresponding
component policy or to an external parent group, then last one is used.
In the following example, component policies P1 and P2 create the merged policy
mpl_88000001.
host1#show policy-list P1
IP Policy P1
Administrative state: enable
Reference count:
Classifier control list: *, precedence 100, parent-group Z
forward
Classifier control list: A, precedence 100, parent-group X
forward
Classifier control list: B, precedence 100, parent-group X
forward
Classifier control list: C, precedence 100, external parent-group EPG1
parameter foo
forward
Classifier control list: D, precedence 100, external parent-group EPG1 parameter
foo
forward
Parent group: X, parent-group Z
rate-limit-profile R1
Parent group: Z
rate-limit-profile R2
host1#show policy-list P2
IP Policy P2
Administrative state: enable
Reference count:
Classifier control list: B, precedence 100, parent-group X
forward
Classifier control list: C, precedence 100, parent-group Y
forward
Policy Table
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1
Policy Table
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1
Parent Group Merge Algorithm
Chapter 6: Merging Policies
121